Bernd Kowall

Wolfgang Rathmann
email: rathmann@ddz.uni-duesseldorf.de

Klaus Strassburger

Christine Meisinger

Rolf Holle

Andreas Mielck

Dr. med W Rathmann

Socioeconomic Status is not associated with Type 2 Diabetes Incidence in an Elderly Population in Germany: KORA S4/F4 Cohort Study

Keywords: Type 2 diabetes, prediabetes, socioeconomic status, elderly population T2DM, type 2 diabetes mellitus, SES, socioeconomic status, OGTT, oral glucose tolerance test, IFG, impaired fasting glucose, IGT, impaired glucose tolerance, CI, confidence interval, OR, odds ratio

Abstract

Background

An association between socioeconomic status (SES) and incidence of type 2 diabetes mellitus (T2DM) has been found for younger and middle-aged subjects, but studies of this relationship in elderly populations are rare.

Methods

In a population-based cohort in Southern Germany (KORA S4/F4: 1,223 subjects aged 55-74 years at baseline, 887 subjects (73%) in the follow-up seven years later), identification of incident T2DM was based on oral glucose tolerance tests or on validated physician diagnoses. Regression models were fitted to predict incident T2DM and (pre)diabetes respectively, with SES as the main independent variable. (Pre)diabetes here means incident T2DM or incident prediabetes.

Results

With five different SES measures (global Helmert index, income, educational level, occupational status, subjective social status), the diabetes risk of low SES groups was not significantly different from the risk of higher SES groups (i.e., cumulative incidence 10% (low income), 9% (medium income), 13% (high income)). In subjects with normoglycemia at baseline, (pre)diabetes incidence was more pronounced in lower SES groups, but almost all these associations were not significant.

With measures of subjective SES stronger associations were found than with measures of objective SES.

Conclusion

There was no statistically significant association between objective SES and diabetes incidence in this elderly population. This might be due to a larger socioeconomic homogeneity of elderly populations and to a strong driving force for diabetes, which outweighed the influence of SES, and which was indicated by an adverse baseline metabolic profile in participants developing diabetes in the follow-up.

Introduction

Previous studies have shown an inverse association between measures of socioeconomic status (SES) and incidence of type 2 diabetes (T2DM). [START_REF] Barker | Incidence of diabetes amongst people aged 18-50 years in nine British towns: A collaborative study[END_REF][START_REF] Haffner | Increased incidence of type II diabetes mellitus in Mexican Americans[END_REF][START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF][START_REF] Morikawa | Ten-year follow-up study on the relation between the development of non-insulin-dependent diabetes mellitus and occupation[END_REF][START_REF] Resnick | Differential effects of BMI on diabetes risk among black and white Americans[END_REF][START_REF] Burke | Rapid rise in the incidence of type 2 diabetes from 1987 to 1996[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF][START_REF] Cox | Locality deprivation and type 2 diabetes incidence: A local test of relative inequalities[END_REF][START_REF] Lidfeldt | A prospective study of childhood and adult socioeconomic status and incidence of type 2 diabetes in women[END_REF][START_REF] Valdés | Population-based incidence of type 2 diabetes in Northern Spain: The Asturias Study[END_REF][START_REF] Maty | Childhood socioeconomic position, gender, adult body mass index, and incidence of type2 diabetes mellitus over 34 years in the Alameda County Study[END_REF] However, most of these studies did not use oral glucose tolerance tests (OGTT) to identify diabetes cases. [START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF][START_REF] Resnick | Differential effects of BMI on diabetes risk among black and white Americans[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF][START_REF] Maty | Childhood socioeconomic position, gender, adult body mass index, and incidence of type2 diabetes mellitus over 34 years in the Alameda County Study[END_REF] Other studies did not measure the SES on an individual level, [START_REF] Barker | Incidence of diabetes amongst people aged 18-50 years in nine British towns: A collaborative study[END_REF][START_REF] Cox | Locality deprivation and type 2 diabetes incidence: A local test of relative inequalities[END_REF] or only used "type of neighborhood" as predictor variable. [START_REF] Burke | Rapid rise in the incidence of type 2 diabetes from 1987 to 1996[END_REF] Furthermore, some were confined to very specific populations like nurses or male factory workers. [START_REF] Morikawa | Ten-year follow-up study on the relation between the development of non-insulin-dependent diabetes mellitus and occupation[END_REF][START_REF] Lidfeldt | A prospective study of childhood and adult socioeconomic status and incidence of type 2 diabetes in women[END_REF] In particular, there is only little evidence whether the inverse association between SES and diabetes incidence also holds for elderly populations, and with few exceptions [START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF] the studies examined populations of younger or middle-aged subjects, or they comprised several age groups. In most studies, education [2, 3, 5, 8, 9-11, 13, 14] and occupational status [START_REF] Morikawa | Ten-year follow-up study on the relation between the development of non-insulin-dependent diabetes mellitus and occupation[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Lidfeldt | A prospective study of childhood and adult socioeconomic status and incidence of type 2 diabetes in women[END_REF][START_REF] Valdés | Population-based incidence of type 2 diabetes in Northern Spain: The Asturias Study[END_REF] were used as measures of SES, while income [START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF] was used less often. However, indices of SES measure different aspects of the mechanisms between SES and health outcomes and they cannot be used interchangeably. [START_REF] Geyer | Education, income, and occupational class cannot be used interchangeably in social epidemiology. Empirical evidence against a common practice[END_REF] Moreover, the association between the subjective SES and T2DM has only rarely been investigated in the elderly. [START_REF] Demakakos | Socioeconomic status and health: the role of subjective social status[END_REF] This study used data of a population-based cohort of elderly subjects to examine the relationship between objective and subjective SES, respectively, and diabetes incidence. Most incident diabetic cases in KORA S4/F4 were prediabetic at baseline. [START_REF] Rathmann | Incidence of type 2 diabetes in the elderly German population and the effect of clinical and lifestyle risk factors: KORA S4/F4 cohort study[END_REF] To examine additionally the relationship between social status and diabetes in subjects who were normoglycemic at baseline we chose (pre)diabetes -(pre)diabetes here means incident type 2 diabetes or prediabetes -as outcome variable for two reasons: with T2DM cases as outcome, the power of the analyses with normoglycemic subjects might be too small; and, moreover, analyses should not be confined to T2DM because prediabetes already increases the risk for coronary heart disease and is often associated with an unfavorable metabolic profile. [START_REF] Rathmann | High prevalence of undiagnosed diabetes mellitus in Southern Germany: Target populations for efficient screening. The KORA survey[END_REF] We used OGTT to identify new diabetes cases, and we used income, education and occupational status separately as SES measures in addition to an SES measure combining these three indicators.

Methods

Study population

The KORA (Cooperative Health Research in the Region of Augsburg) Survey is a population-based study in Southern Germany using the same region and study methods as the previous WHO MONICA Augsburg project. 2,656 subjects in the age of 55 to 74 years were invited to participate in 1999, and 1,653 (62%) subjects were investigated. 131 subjects with known diabetes were excluded, and after exclusion of further drop-outs 1,353 nondiabetic subjects underwent an OGTT at baseline. This recruitment process has been described in more detail earlier. [START_REF] Rathmann | High prevalence of undiagnosed diabetes mellitus in Southern Germany: Target populations for efficient screening. The KORA survey[END_REF] All subjects with completed OGTT at baseline were re-invited in 2006 to 2008. The present study includes all subjects without known or newly diagnosed diabetes at baseline (n=1,223). Among these subjects, 98 had died before the time of the follow-up examination, and 887 (73%) subjects participated in the follow-up. Informed consent was obtained from the participants. The survey was approved by the ethics committee of the Bavarian Medical Association.

Definition of SES variables

SES indicators were assessed in a structured health interview performed by trained investigators.

Scores for educational level, occupational status and income were assigned based on a scheme developed by Helmert for the German population. [START_REF] Helmert | Poverty and health in West Germany[END_REF][START_REF] Helmert | Soziale Ungleichheit und Krankheitsrisiken[END_REF] The highest score either for school education or vocational training was used for the educational level. School education was based on the highest level obtained (primary, secondary, tertiary school or university degree), and three categories for vocational training were distinguished. Subjects´ reported occupations were grouped in a social class hierarchy proposed by Helmert and Sheafor the German labour market. [START_REF] Helmert | Social inequalities and health status in Western Germany[END_REF] For retired persons, their latest occupation was coded. Among persons without regular employment (e.g. housewives) the occupation of the spouse was used as a proxy. Equivalent household income was categorized as less than 50%, 50 -100%, 101 -150%, 151 -200%, and more than 200% of the median income. Scores ranged from 1 to 9 (income, occupation), and 0 to 9 (education), respectively, and were added up to build a global score for SES.

For regression analyses, subjects were grouped into three categories for the global SES as well as for educational level, occupational status and income. According to the literature, [START_REF] Helmert | Soziale Ungleichheit und Krankheitsrisiken[END_REF] these categories were the following for the global SES: low SES = scores from 2 to 8; medium SES = scores from 9 to 18; high SES = 19 to 27. For education, occupation and income, categories were as follows: scores up to 3 = low status; scores from 4 to 6 = medium status; scores from 7 to 9 = high status.

To assess subjective SES, subjects were asked to which social class they belonged in their own view.

Categories were combined as follows: low subjective status (lower or working class), medium subjective status (medium class), high subjective status (upper medium or upper class).

Ascertainment of type 2 diabetes and prediabetes

Subjects who reported a physician diagnosis of diabetes or use of anti-diabetic medications were classified as incident diabetes cases, their reports were validated by contacting the general practitioners who had treated them. For the remaining subjects, OGTT with a 75 g oral load of anhydrous glucose were conducted to ascertain diabetes status. OGTT were performed in the morning hours (7:00 to 11:00 h). Subjects were instructed to fast for 10 hours overnight, to avoid heavy physical activity and not to smoke before or during the OGTT. Subjects with fever, infections or acute gastrointestinal diseases were excluded from the test. Impaired fasting glucose, impaired glucose tolerance and newly diagnosed diabetes were defined according to 1999 WHO criteria. [START_REF] Alberti | Definition, diagnosis and classification of diabetes mellitus and its classifications. Part 1: Diagnosis and classification of diabetes mellitus. Provisional report of a WHO consultation[END_REF] Prediabetes comprised isolated IFG, isolated IGT and combined IFG and IGT. Newly diagnosed type 2 diabetes (OGTT) and validated physician diagnosis were considered as incident type 2 diabetes. Anthropometric measurements and laboratory measurements have been described elsewhere. [START_REF] Helmert | Poverty and health in West Germany[END_REF] Information about sociodemographic variables, medical history, smoking, alcohol consumption, and physical activity was gathered in a structured interview. Dietary intake was assessed with a short 27 item qualitative food frequency list (FFL). Details on a very similar FFL have been described elsewhere. [START_REF] Winkler | Validation of a short qualitative food frequency list used in several German large scale surveys[END_REF]

Statistical analysis

Baseline characteristics of subjects with low, medium or high global SES were compared using F-tests or χ 2 -tests. For subjects with and without diabetes in the follow-up, medians of the Helmert SES scores were compared using the Mann-Whitney U-test. For all subjects, the proportion of incident diabetes cases, and for the subgroup of subjects with normoglycemia at baseline, the proportion of incident (pre)diabetes cases was calculated for each level of the different SES measures. Significance of differences in these proportions between SES levels was tested using χ 2 -tests.

Multivariate logistic regression models were fitted to calculate odds ratios with 95% confidence intervals for the relationship between SES variables and diabetes or (pre)diabetes. Five different SES measures (global SES, educational level, occupational status, income, and subjective social status) were used separately in each set of analyses. In a first set of analyses, all 887 subjects were included, and the association between SES and the incidence of diabetes was assessed. In a second set of analyses, only subjects with normoglycemia (no prediabetes) at baseline were considered, and the relationship between SES and the incidence of (pre)diabetes was assessed. As there is some evidence for a gender-specific SES-diabetes relationship, [8, 25 26] interaction terms (interaction between SES and sex) were tested for significance, and analyses were additionally done separately for men and women.

Covariables considered either as potential confounders or as possible mediators of the association between SES and diabetes or (pre)diabetes were included in the regression models. For the two sets of analyses (with diabetes or (pre)diabetes as outcome variables), three different models were examined:

(1) models adjusted only for age and sex as possible confounders; (2) models additionally adjusted for age, sex, and lifestyle factors (smoking, alcohol consumption, physical activity, intake of meat and sausage, intake of salad and vegetables, intake of whole-grain bread, coffee consumption); [START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF] models additionally adjusted for components of the metabolic syndrome (waist circumference, blood pressure, triglycerides, level of HDL-cholesterol). Thus, in models 2 and 3 lifestyle factors and cardiometabolic factors as possible mediators of the association between SES and diabetes incidence are included in order to look for possible pathways between SES and diabetes incidence.

The covariables were dichotomized as follows: age at baseline: 55-64 and 65-74 years; family status: living with a partner / living alone; smoking: current smokers / ex-and non-smokers; high alcohol intake: >40 g/day in men, >20 g/day in women; high physical activity: at least one hour of sports per week during leisure time in either summer or winter; large waist circumference ≥102 cm and ≥88 cm for men and women, respectively; hypertension: blood pressure of 140 / 90 mmHg or higher, or antihypertensive medication, given that the subjects were aware of being hypertensive; low HDLcholesterol: <40 mg/dl in males, <50 mg/dl in women; hypertriglyceridemia ≥2.0 mmol/l; intake of meat and sausage (intake of meat, sausage or ham almost daily or several times a week); intake of salad and vegetables (intake of salad, cooked or uncooked vegetables almost daily or several times a week); intake of whole-grain bread (intake of whole-grain bread, brown bread or crispbread almost daily or several times a week); coffee consumption (more than three cups of coffee a day).

In addition to the logistic regression models, linear regression models were fitted using change of 2 hour glucose between baseline and follow-up as outcome variable, and 2 hour glucose at baseline was included in the models.

The level of statistical significance was 5%. The analyses were carried out using SAS version 9.1.3 (SAS institute, Cary, NC, USA).

Results

For males, only few significant differences were found between the socioeconomic status groups (table 1). Men in higher SES groups were taller and were more physically active than men in lower SES groups. Wine intake was higher in the high SES group, whereas the proportion of current smokers was slightly lower in the high SES group. Moreover, social status groups of male participants did not differ in the various components of the metabolic syndrome. In women, as opposed to men, overweight was significantly more common in the low SES group. However, the proportion of overweight women with a body mass index larger than 25kg/m 2 was also rather high in the high SES group (62% compared to 82% in the low SES group). Smoking and alcohol intake were more common in women of higher SES. Concerning other components of the metabolic syndrome like HDLcholesterol, triglycerides, and blood pressure, there were no significant differences in women. For subjective physical health, clear differences were found between the SES groups for both sexes.

Thirty-one percent of low SES males, 19% of medium SES males, but only 12% of high SES males considered their health status as less good or even bad (p=0.02). For females, the corresponding figures were 26%, 20% and 11%, respectively (p=0.10).

Subjects did not differ in their median of the Helmert scores with regard to incident diabetes (in men: both median=14 for subjects with and without diabetes, p=0.95; in women: median=12 for subjects without and median=13 for subjects with diabetes, p=0.68). Table 2 shows the results of crude analyses of the associations between SES and diabetes / (pre)diabetes. The proportion of incident diabetes cases was slightly higher for high SES groups, with the exception of the subjective social status, where most incident diabetes cases were found for the low status group. The proportion of incident (pre)diabetes cases among subjects with baseline normoglycemia was lowest in the high status groups for all five SES measures. 95%CI: 0.8-3.7) and which decreased upon including possible mediators. In linear regression models with changes in 2h-glucose between baseline and follow-up as outcome variable, there were no significant relationships between SES and changes in 2h-glucose for all SES measures (data not shown).

Table 4 presents models which predict the risk of (pre)diabetes of subjects with baseline normoglycemia. Except for occupational status, the odds ratios were all larger than one, indicating that the risk of (pre)diabetes is higher for low as compared with high SES groups. Some odds ratios showed a borderline significance, but just one odds ratio reached the level of statistical significance.

Subjects with medium subjective social status had a significantly increased (pre)diabetes risk in the model adjusted for age and sex (OR: 2.2; 95%-CI: 1.1-4.5). The odds ratios were slightly reduced after adjusting for further variables.

In the regression models in tables 3 and 4, interaction terms of SES and sex were not statistically significant and, therefore, were excluded from the models. In addition, sex-specific regression models were fitted, which showed results for the association of SES and diabetes / (pre)diabetes incidence which were comparable with the results without stratification by sex (data not shown). 1.0 (0.6-1.7) 0.8 (0.4-1.3) 1 0.9 (0.5-1.5) 0.7 (0.4-1.3) 1 0.9 (0.5-1.6) 0.8 (0.5-1.

Discussion

Our study showed that objective SES measures (global Helmert index, income, occupation, educational level) were not associated with type 2 diabetes incidence in an elderly population in a statistically significant way. Among subjects with normoglycemia at baseline, there were more cases of incident (pre)diabetes in the low SES group than in the high SES group, but these associations were not significant for the various measures of objective SES. When using subjective social status instead of objective measures of social status, we found stronger relationships between diabetes and (pre)diabetes, respectively, and social status.

The lack of a relationship between objective SES and diabetes incidence in our study is not in line with the literature where inverse relationships were reported. [START_REF] Barker | Incidence of diabetes amongst people aged 18-50 years in nine British towns: A collaborative study[END_REF][START_REF] Haffner | Increased incidence of type II diabetes mellitus in Mexican Americans[END_REF][START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF][START_REF] Morikawa | Ten-year follow-up study on the relation between the development of non-insulin-dependent diabetes mellitus and occupation[END_REF][START_REF] Resnick | Differential effects of BMI on diabetes risk among black and white Americans[END_REF][START_REF] Burke | Rapid rise in the incidence of type 2 diabetes from 1987 to 1996[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF][START_REF] Cox | Locality deprivation and type 2 diabetes incidence: A local test of relative inequalities[END_REF][START_REF] Lidfeldt | A prospective study of childhood and adult socioeconomic status and incidence of type 2 diabetes in women[END_REF][START_REF] Valdés | Population-based incidence of type 2 diabetes in Northern Spain: The Asturias Study[END_REF][START_REF] Maty | Childhood socioeconomic position, gender, adult body mass index, and incidence of type2 diabetes mellitus over 34 years in the Alameda County Study[END_REF]However, our study differed from the published studies in one important aspect: we have investigated an elderly population aged 55 to 74 years at baseline whereas in most other studies (exceptions [START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF] see below) either middle-aged study populations or cohorts comprising several age groups were investigated. In the Health and

Retirement Study with subjects aged 51 years and older a negative impact of low on diabetes onset was shown only for women. [START_REF] Best | Life course pathways to adult-onset diabetes[END_REF] A US American comparing two cohorts of middle-aged (51-61 years) and older adults (>70 years) found that effects of social status were reduced in the elderly cohort. [START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF] This suggests that old age has an important impact on the association between SES and diabetes incidence. To explain the lack of an association between the objective SES and diabetes incidence and the stronger association between the subjective SES and diabetes risk, three explanations are conceivable:

(1) An accurate measurement of objective SES is problematic in the elderly for several reasons. [START_REF] Grundy | The socioeconomic status of older adults: How should we measure it in studies of health inequalities?[END_REF] Links between working conditions and health as captured by the occupational status may still influence health in old age, but may also be attenuated after retirement. To give a second example, in old age income is often drawn from several sources and is, therefore, more difficult to measure accurately. However, it was suggested that the subjective SES is a more sensitive measure of social status capturing more nuances of the socioeconomic position and of life-time achievement. [START_REF] Demakakos | Socioeconomic status and health: the role of subjective social status[END_REF][START_REF] Singh-Manoux | Does subjective social status predict health and change in health status better than objective status?[END_REF] Accordingly, in a cross-sectional study in six European countries with subjects aged between 50 and 65 years, subjective SES was shown to be stronger related to health outcome than income. [START_REF] Theodossiou | The social gradient in health: The effect of absolute income and subjective social status assessment on the individual´s health in Europe[END_REF] Studies about subjective SES and diabetes in old age are rare; with cross-sectional data of the English Longitudinal Study of Ageing, a strong relation between subjective SES and diabetes prevalence was found. [START_REF] Demakakos | Socioeconomic status and health: the role of subjective social status[END_REF] In our study, only one in four odds ratios for the association between subjective SES and the incidence of diabetes/(pre)diabetes was statistically significant, and the (pre)diabetes risk was larger for subjects with medium subjective SES than for subjects with low subjective SES (compared to high subjective SES). In the light of these results, it is suggested that the association between subjective SES and diabetes in the elderly should be further investigated.

(2) Apart from problems of measuring SES, there are other factors possibly contributing to a weaker relationship between SES and health status in the KORA cohort. Most subjects born in the 1930s and 1940s in Germany had a similar (low) school education. Thus, in that age group, subjects with low levels of formal education were not that underprivileged as it is the case today, and thus lower education probably had less negative impacts on health. Moreover, as can be seen from table 1, differences between status groups are not much pronounced in many regards.

(3) Subjects developing diabetes in the follow-up already had much larger fasting and 2h-glucose concentrations at baseline (data not shown), and accordingly, most subjects with diabetes in the follow-up had prediabetes at baseline. In addition, subjects getting the disease in the follow-up also had more adverse metabolic risk factors (HDL-cholesterol, adiponectin, serum uric acid,data not shown) at baseline than subjects without diabetes in the follow-up. Not all the subjects with increased glucose values at baseline finally developed diabetes, but these results support the assumption that the development of diabetes is determined by risk factors acting long before the onset of the disease. Thus, in older subjects with adverse clinical data at baseline, SES may have less influence on the progression towards diabetes.

One might argue that the KORA population is not representative. There might have been a selection bias due to earlier death and lower response rates of less wealthy and less healthy people resulting in more homogeneous elderly populations, leading to an attrition of the SES-health relationship.

Moreover, some characteristics of the population seem to be somewhat unusual: high SES women show an elevated level of smoking and alcohol consumption compared to low SES women, and in men, there is a lack of differences in the metabolic profiles between the SES groups. However, for SES differences concerning alcohol and smoking in women, and metabolic syndrome components in men there is little data for the elderly. In Germany, it was shown that consumption of alcohol is elevated in women with high SES. [START_REF] Baumeister | Riskanter Alkoholkonsum und alkoholbezogene Störungen in Vorpommern: Die Studie 'Leben und Gesundheit in Vorpommern' (SHIP) und der Bundesgesundheitssurvey 1998 im Vergleich[END_REF] Some limitations may have affected our results. First, there was a healthy participant effect. The 336 non-participants were less healthy and had a lower social status than the 887 participants included here (data not shown). If there were more diabetes cases in the subjects lost to follow-up the influence of low SES on diabetes incidence would have been underestimated. Second, the number of incident diabetes cases was quite small for the low / high levels of some SES measures. However, our results

were consistent for all objective SES measures; using a continuous variable as SES measure allowed the comparisons of much larger groups (e.g., 60 diabetic versus 387 non-diabetic subjects in men) and also showed no differences in subjects with and without diabetes.

Our study has several strengths. It was based on a well-defined population, and we used several different SES measures in the analyses. Our analyses were adjusted for lifestyle factors and for components of the metabolic syndrome, and, contrary to most other studies, [START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF][START_REF] Resnick | Differential effects of BMI on diabetes risk among black and white Americans[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF][START_REF] Maty | Childhood socioeconomic position, gender, adult body mass index, and incidence of type2 diabetes mellitus over 34 years in the Alameda County Study[END_REF] diabetes incidence was assessed by OGTT in addition to validated self-reports.

In conclusion, this study suggests that the inverse association between objective SES and diabetes incidence which was found for younger and middle-aged populations [START_REF] Barker | Incidence of diabetes amongst people aged 18-50 years in nine British towns: A collaborative study[END_REF][START_REF] Haffner | Increased incidence of type II diabetes mellitus in Mexican Americans[END_REF][START_REF] Lipton | Determinants of incident non-insulin-dependent diabetes mellitus among blacks and whites in a national sample: The NHANES I Epidemiologic Follow-up Study[END_REF][START_REF] Morikawa | Ten-year follow-up study on the relation between the development of non-insulin-dependent diabetes mellitus and occupation[END_REF][START_REF] Resnick | Differential effects of BMI on diabetes risk among black and white Americans[END_REF][START_REF] Burke | Rapid rise in the incidence of type 2 diabetes from 1987 to 1996[END_REF][START_REF] Kumari | Prospective study of social and other risk factors for incidence of type 2 diabetes in the Whitehall II Study[END_REF][START_REF] Best | Life course pathways to adult-onset diabetes[END_REF][START_REF] Maty | Education, income, occupation, and the 34-year incidence (1965-99) of type 2 diabetes in the Alameda County Study[END_REF][START_REF] Robbins | Socioeconomic status and diagnosed diabetes incidence[END_REF][START_REF] Wray | Social status, risky health behaviors, and diabetes in middle-aged and older adults[END_REF][START_REF] Cox | Locality deprivation and type 2 diabetes incidence: A local test of relative inequalities[END_REF][START_REF] Lidfeldt | A prospective study of childhood and adult socioeconomic status and incidence of type 2 diabetes in women[END_REF][START_REF] Valdés | Population-based incidence of type 2 diabetes in Northern Spain: The Asturias Study[END_REF][START_REF] Maty | Childhood socioeconomic position, gender, adult body mass index, and incidence of type2 diabetes mellitus over 34 years in the Alameda County Study[END_REF] cannot be taken for granted for elderly populations. For this age group, the exact nature of the association between SES and diabetes incidence needs further investigation.

What is known on this subject

Several studies found an inverse association between the socioeconomic status and the incidence of diabetes in younger and middle-aged populations. However, there is not much evidence concerning the question whether this association also holds true for elderly populations.

What this study adds

This study shows that an inverse relationship between the objective socioeconomic status and diabetes incidence cannot simply be taken for granted in elderly populations. For a German cohort of 55 to 74 year old subjects an inverse association between SES and diabetes incidence was not found neither for men nor for women. Elderly people developing a new type 2 diabetes display an adverse metabolic risk profile years before the onset of diabetes so that a strong force for diabetes seems to outweigh the potential influence of the socioeconomic status.

Public health implications

This study supports the claim that health inequalities have to be studied for each age group separately.

It suggests that health inequalities in older age groups could be less pronounced than in younger age groups, and that this lack of an association between socioeconomic status and health is very well compatible with the fact that these associations are found earlier in the life course.

1 :

 1 adjusted for age and sex b Model 2: like Model 1, + smoking, alcohol intake, physical activity and diet (intake of meat and sausage, of salad and vegetables, of whole-grain bread, and coffee consumption) c Model 3: like Model 2, + blood pressure, hypertriglyceridemia, waist circumference, HDL-Cholesterol

Table 1

 1 Baseline characteristics of status groups (global Helmert index) by sex: KORA S4/F4 (Augsburg, Southern Germany) a

			Males			Females
		Low SES	Medium	High SES P value b	Low	Medium	High	P value b
			SES			SES	SES	SES
	N	49	284	115		106	286	45
	Age (years)	64.7 (5.1)	63.3 (5.5)	63.1 (5.7)	0.21	64.0	62.7 (5.2)	62.6	0.07
						(5.0)		(6.2)
	Body length (cm) 169.7	172.0 (6.3)	174.3	0.0001**	157.4	159.9	161.5	0.0001**
		(4.9)		(6.4)		(5.3)	(5.9)	(5.9)
	BMI (kg/m 2 )	28.6 (3.7)	28.0 (3.4)	27.9 (3.2)	0.40	29.5	27.9 (4.5)	26.3	0.0001**
						(4.8)		(3.7)
	Overweights	87.8	82.8	84.8	0.64	82.1	75.5	62.2	0.03*
	(BMI ≥ 25) (%)
	Waist	101.6	99.4 (9.0)	99.6 (8.6)	0.28	92.0	88.6	84.8	0.0003**
	circumference	(9.7)				(11.7)	(10.1)	(8.8)
	(cm)
	Alcohol intake	83.3	87.3	87.0	0.76	57.6	66.4	75.6	0.08
	>0 g/day (%)
	Beer intake	77.1	78.5	71.3	0.31	31.1	37.8	24.4	0.15
	> 0 g/day (%)
	Wine intake	29.2	38.9	65.2	0.0001**	33.0	43.7	62.2	0.004**
	> 0 g/day (%)
	Current smokers	16.7	15.9	12.2	0.61	3.8	11.5	11.1	0.06
	(%)
	Systolic blood	138.0	138.4 (17.4) 136.2	0.53	128.5	127.8	129.8	0.78
	pressure (mmHg)	(19.3)		(18.8)		(18.4)	(18.8)	(16.8)
	Diastolic blood	80.2	82.0 (9.7)	83.8	0.10	77.0	77.3 (9.7)	77.3	0.95
	pressure (mmHg)	(11.2)		(10.6)		(10.0)		(9.1)
	HDL-Cholesterol	55.5	53.1 (13.1)	55.1	0.28	64.0	64.2	69.5	0.14
	(mg /dl)	(13.9)		(14.7)		(16.6)	(16.8)	(18.3)
	LDL-Cholesterol	145.7	155.7 (36.5) 149.8	0.13	158.3	156.1	156.3	0.90
	(mg /dl)	(37.2)		(41.5)		(43.0)	(39.9)	(44.8)
	Triglycerides	141.5	139.2	135.9	0.91	123.1	116.8	105.1	0.17
	(mg /dl)	(105.3)	(79.5)	(80.8)		(53.6)	(54.4)	(50.3)
	Physically active	27.1	45.6	49.6	0.03*	34.9	53.9	57.8	0.002**
	(%)
	Less good or bad	31.3	19.1	12.2	0.02*	26.4	20.3	11.1	0.10
	subjective health
	status (%)
	*p<0.05, **p<0.01
	a Standard deviations given in brackets
	b P values by F-test or χ 2 -test

Table 2

 2 Incidence of diabetes and (pre)diabetes a by level of different SES measures: KORA S4/F4 (Augsburg, Southern Germany)

		All	Incident	p	Subjects with	Incident	p
		subjects	diabetes	value e	normoglycemia	(pre)diabetes a	value e
			cases		at baseline	cases
	Global
	socioeconomic
	status b
	Low	155	13 (8.4 %)		113	32 (28.3%)
	Medium	570	59 (10.4 %)		416	118 (28.4%)
	High	160	21 (13.1 %)	0.38	118	24 (20.3%)	0.21
	Education c
	Low	482	49 (10.2 %)		354	100 (28.3%)
	Medium	276	28 (10.1 %)		204	53 (26.0%)
	High	128	16 (12.5 %)	0.73	90	22 (24.4%)	0.71
	Income c
	Low	263	26 (9.9 %)		196	59 (30.1%)
	Medium	392	37 (9.4 %)		285	77 (27.0%)
	High	186	25 (13.4 %)	0.32	132	28 (21.2%)	0.20
	Occupational
	status c
	Low	323	35 (10.8 %)		232	60 (25.9%)
	Medium	324	29 (9.0 %)		236	68 (28.8%)
	High	220	28 (12.7 %)	0.37	163	40 (24.5%)	0.60
	Subjective
	social status d
	Low	248	39 (15.7 %)		173	42 (24.3%)
	Medium	522	43 (8.2 %)		392	114 (29.1%)
	High	92	9 (9.8 %)	0.01*	63	10 (15.9%)	0.07
	*p<0.05
	a (Pre)diabetes means prediabetes (IFG/IGT) or diabetes
	b Global socioeconomic status groups were built according to Helmert scores (low: 2-8, medium 9-18, high 19-
	27)

c

Helmert scores for education, income and occupational status were classified into three groups (low: up to 3, medium: 4-6, high: 7-9) d Self-assessments were categorized into three groups (low subjective status (lower or working class), medium subjective status (medium class), high subjective status (upper medium or upper class)) e χ 2 -test

Table 3

 3 presents the results of multivariate logistic regressions fitting diabetes risks of subjects who were normoglycemic or prediabetic at baseline. The risk of diabetes in the seven year follow-up was neither associated with the global SES nor with educational level, income and occupational status. In model 1 adjusted only for age and sex, subjects with low global SES did not have a larger risk of diabetes than subjects with high global SES (OR: 0.7; 95%CI: 0.3-1.6). Additional adjusting for lifestyle factors (model 2) and for components of the metabolic syndrome (model 3) had only small impacts on the odds ratios. So, for global SES, education, income and occupational status odds ratios were one or even smaller than one. Subjects with low subjective SES had a somewhat increased risk of diabetes than subjects with high subjective SES which was nevertheless not significant (OR: 1.7;

Table 3

 3 Association of SES measures with type 2 diabetes incidence in the follow-up: multivariate logistic regression analyses with 887 subjects without diabetes at baseline (low and medium SES group, respectively, versus high SES group, odds ratios with 95% confidence intervals; dependent variable = diabetes incidence in the follow-up)

	Model 1 a	Model 2 b	Model 3 c

Table 4

 4 Association of SES measures with (pre)diabetes a incidence in the follow-up: multivariate logistic regression analyses with 649 subjects with normoglycemia at baseline (low and medium SES group, respectively, versus high SES group, odds ratios with 95% confidence intervals; dependent variable = (pre)diabetes a incidence in the follow-up)

			Model 1 b	Model 2 c	Model 3 d
	Global SES	low SES	1.6	1.3	1.1
			(0.8-2.9)	(0.7-2.5)	(0.6-2.2)
		medium SES	1.6	1.5	1.4
			(0.96-2.6)	(0.9-2.5)	(0.8-2.3)
		high SES (ref)	1	1	1
	Education	low SES	1.2	1.1	1.1
			(0.7-2.1)	(0.6-2.0)	(06-2.0)
		medium SES	1.1	1.1	1.1
			(0.6-2.0)	(0.6-2.0)	(0.6-2.0)
		high SES (ref)	1	1	1
	Income	low SES	1.5	1.4	1. 2
			(0.9-2.6)	(0.8-2.3)	(0.7-2.1)
		medium SES	1.3	1.3	1.3
			(0.8-2.1)	(0.8-2.1)	(0.8-2.2)
		high SES (ref)	1	1	1
	Occupational	low SES	1.1	1.0	1.0
	status		(0.7-1.8)	(0.6-1.6)	(0.6-1.6)
		medium SES	1.3	1.4	1.4
			(0.8-2.1)	(0.9-2.2)	(0.9-2.3)
		high SES (ref)	1	1	1
	Subjective	low SES	1.7	1.4	1.2
	social status	medium SES	(0.8-3.6) 2.2	(0.6-3.0) 1.9	(0.6-2.7) 1.8
			(1.1-4.5)	(0.9-4.0)	(0.9-3.8)
		high SES (ref)	1	1	1

a (Pre)diabetes means prediabetes or type 2 diabetes b Model 1: adjusted for age and sex c Model 2: like Model 1, + smoking, alcohol intake, physical activity and diet (intake of meat and sausage, of salad and vegetables, of whole-grain bread, and coffee consumption) d Model 3: like Model 2, + blood pressure, hypertriglyceridemia, waist circumference, HDL-Cholesterol

Acknowledgments

The Diabetes Cohort Study was funded by a German Research Foundation project grant to the corresponding author (DFG; RA 459/2-1). The German Diabetes Center is funded by the German Federal Ministry of Health, and the Ministry of School, Science and Research of the State of North-Rhine-Westfalia. The KORA research platform and the KORA Augsburg studies are financed by the Helmholtz Zentrum München, German Research Center for Environmental Health, which is funded by the German Federal Ministry of Education, Science, Research and Technology and by the State of Bavaria. We thank the field staff in Augsburg who were involved in the conduct of the studies.

Duality of interest

The authors declare that there is no duality of interest associated with this paper.


Ugo Fedeli

Natalia Alba

Francesco Zambon
email: frazambon@libero.it

Francesco Avossa

Paolo Spolaore

Hospitalization for surgical procedures is lower among immigrants than among non-immigrant preschool children: results from a region-wide study in Italy

Keywords: Pediatric Surgery, Immigrants, Health services research, Pediatric hospitalization Word count: 1135

Background: Whether immigrant children receive unnecessary treatments and surgical procedures to a greater extent than non-immigrants remains controversial. The study investigates whether hospitalization rates differ between immigrant and non-immigrant preschool children and the extent to which such differences relate to specific pathological conditions.

Methods

: All discharges occurring to children aged 1-5 years between 2005 and 2007 in the Italian Region of Veneto (4,8 million inhabitants) were analyzed by Diagnosis Related Groups-DRGs. Crude and age-standardized hospitalization rate ratios-RRs of immigrant versus Italian children were computed. Results: Hospitalization rates for medical conditions were similar between immigrant and Italian children. However, hospitalization rates among immigrant children were significantly lower than those among Italians for all the most frequent surgical DRGs. RRs of immigrant versus Italian children were 0.46(0.41-0.51) for tonsillectomy/adenoidectomy and 0.46(0.38-0.57) for testes procedures in males; 0.44(0.38-0.49) for tonsillectomy/adenoidectomy and 0.47(0.34-0.65) for extraocular procedures in females. Only circumcision procedures were more frequent (four-fold excess) among immigrants.

Conclusion:

Hospitalization rates for all most frequent surgical procedures are significantly lower among immigrants compared to non-immigrant preschool children. Reduced surgery rates among immigrants might result from a complex interplay between parental attitudes and knowledge on pediatric conditions, language barriers, and access to primary care.

What is already known on this subject?

Studies on hospitalization rates among immigrant and non-immigrant preschool children have come to conflicting results. On the one hand, an excess of hospitalization, including recourse to unnecessary treatments, has been reported among immigrant compared to non-immigrant children.

On the other hand, hospitalization for specific surgical procedures has been found lower among immigrants.

What does this study add?

Hospitalization rates for medical conditions are similar among immigrant and non-immigrant preschool children. However, hospitalization rates for surgical procedures are significantly lower among immigrants.

Such differences are vast and registered for all the most frequent surgical procedures.

INTRODUCTION

Studies on pediatric hospitalization suggest that a large proportion of admissions are discretionary. [START_REF] Mcconnochie | Socioeconomic variation in discretionary and mandatory hospitalization of infants: an ecologic analysis[END_REF][START_REF] Perrin | Variations in rates of hospitalization of children in three urban communities[END_REF][START_REF] Goodman | Why are children hospitalized? The role of non-clinical factors in pediatric hospitalizations[END_REF] However, whether this discretion applies to hospitalization of children born to immigrants remain controversial.

On the one hand it has been found that immigrant children carry a greater risk of receiving unnecessary surgical treatments and, in general, have hospitalization rates higher than native-born children. [START_REF] Bisset | Grommets, tonsillectomies, and deprivation in Scotland[END_REF][START_REF] Materia | Health care inequalities: hospitalization and socioeconomic position in Rome[END_REF][START_REF] Materia | The clinical and organisational appropriateness of tonsillectomy and adenoidectomy-an Italian perspective[END_REF][START_REF] Danielsson | Hospitalization in Sweden of children born to immigrants[END_REF] On the other hand, hospitalization for certain elective surgical procedures has been found lower in immigrant children than in non-immigrant classmates. [START_REF] Fedeli | Variability of adenoidectomy/tonsillectomy rates among children of the Veneto Region, Italy[END_REF][9][START_REF] Derose | Immigrants and Health Care Access, Quality and Cost[END_REF] This study investigates whether hospitalization rates differ among immigrant and non-immigrant preschool children and the extent to which such differences, if any, relate to specific surgical procedures.

METHODS

The study was carried in Veneto, an Italian Region with a population of 4.8 million (January 2007).

In Italy each child with regular residency (irrespective of citizenship) has access to a family pediatrician, who provides ambulatory care and refers to other specialists in case of need; hospital care in public hospitals is free, covered by general taxation.

Hospital admissions for all causes occurring from January 1st 2005 to December 31st 2007 to residents in Veneto aged 1-5 years were extracted from the regional archive of the Hospital Discharge Records-HDR. Such archive includes discharges for all medical and surgical procedures from public and private health service providers, and also includes discharges of residents hospitalized outside the Region.

The mean study population consisted of 227097 children (51% males), of which 13% were immigrant. For the purpose of this study we defined as immigrant those children with foreign citizenship (born outside Italy or born in Italy to foreign parents). The proportion of children born in Italy from foreign parents is rising; in 2007 these latter were mainly from Eastern Europe (42%), Northern Africa (22%), Central and Southern Africa (12%), and Asia (22%). We obtained figures on the Veneto population by gender, age and citizenship from the Italian Institute of Statistics website [11].

In order to deal with a more homogeneous population the analysis was restricted to preschool As data were anonymized, patients with repeated admissions could not be identified. All analyses were carried out using Stata, version 9.

RESULTS

There were 64975 discharges among children aged 1-5 years in the study period; of these 43024 (66%) hospital admissions were related to medical and 21951 (34%) to surgical DRGs. The most frequent surgical DRGs were tonsillectomy/adenoidectomy (n=11103, 51% out of surgical DRGs), hernia procedures (n=1487, 7%), testes procedures for nonmalignancy (n=1419, 6%), extraocular procedures except orbit (n=1311, 6%), miringotomy with tube insertion (n=727, 3%), penis procedures (n=635, 3%), and circumcision (n=520, 2%).

The overall hospitalization rate was 95.4 per 1000 person-years (32.2 for surgical and 63.2 for medical DRGs). Discharge rates were higher among males than females with such a difference being wider for surgical DRGs (39.8 and 24.2 per 1000 in males and females respectively, with a 64% excess among males) than for medical DRGs (69.6 and 56.3 per 1000, with a 24% excess).

Table 1 shows hospitalization rates by DRG, gender and citizenship (immigrant versus Italian children): the overall recourse to hospital care for medical conditions was similar between immigrant and Italian children, with only slightly lower rates among male, but not among female immigrants.

In sharp contrast with the latter finding, age-standardized RRs indicate that overall surgical hospitalizations among immigrants were reduced by 35% in males and 47% in females. Among immigrant children hospitalization rates were significantly lower than those among Italians for all the most frequent surgical DRGs, but hernia procedures in females; only circumcision was found four times higher among immigrants.

Hospitalization rates for extraocular procedures, tonsillectomy/adenoidectomy, miringotomy, testes and penis procedures among immigrants ranged from one-third to two-thirds of figures detected among Italian children. Once hospitalizations for circumcision procedures were excluded, the RRs for all surgical DRGs in immigrant compared to Italian children was similar among males (0.57) and females (0.53).

DISCUSSION

Hospital admissions for medical conditions did not differ according to citizenship in our study population.

On the contrary, differences in hospitalization rates for surgical procedures between immigrant and Italian children were vast and pertained to all the most frequent surgical procedures.

On the whole surgical procedures, which were mostly represented by elective surgeries, accounted for about one third of the overall recourse to hospital care and involved a large proportion of preschool children, especially Italian males.

Notwithstanding the fact that national guidelines aim at reducing its occurrence, adenoidectomy/tonsillectomy accounted for about half of all discharges. On this regards, barriers in the access of immigrant children to health services may produce a paradoxical protective effect towards inappropriate surgery. [START_REF] Materia | Health care inequalities: hospitalization and socioeconomic position in Rome[END_REF][START_REF] Materia | The clinical and organisational appropriateness of tonsillectomy and adenoidectomy-an Italian perspective[END_REF] Circumcision was the only surgical procedure performed more frequently among immigrant children. Differently from the United States, in Europe circumcision is restricted to medical conditions affecting the foreskin; [START_REF] Cathcart | Trends in paediatric circumcision and its complications in England between 1997 and 2003[END_REF] high rates among foreign children are likely to be explained by ritual circumcision.

Higher hospitalization rates in males compared to females were almost completely explained by sex-specific procedures, as well as by underlying disease rates known to be higher in males (such as hernia procedures), [START_REF] Rajmil | Gender differences in children's hospitalization in Catalonia: another inequality?[END_REF] and by a 33% excess in adenoidectomy/tonsillectomy. It is worth of notice that in our analyses, despite large differences in baseline rates, the male to female ratio of adenoidectomy/tonsillectomy was similar among Italian and immigrant children (Table 1).

Different determinants such as specific underlying pathologies, reduced access to appropriate medical care, or a preferential use of emergency departments in approaching health services may play conflicting roles in shaping the recourse to hospital care among the immigrant population. [START_REF] Danielsson | Hospitalization in Sweden of children born to immigrants[END_REF][START_REF] Buron | Hospital emergency department utilisation rates among the immigrant population in Barcelona, Spain[END_REF] Nonetheless, whilst hospitalization for medical DRGs is similar among Italian and foreign children suggesting that access to acute hospital care is assured to all residents irrespective of citizenship, vast disparities exist in the recourse to elective surgery. Factors such as parental attitudes and knowledge play a relevant role, and drive the four-fold excess in circumcision rates among immigrant children.

Nevertheless, the reduction of surgery rates among the foreign population extends to different otolaryngological, oculistic, urological elective procedures; this suggests difficulties in the access to primary care for appropriate evaluation and referral to the specialist. Such difficulties may arise from parental lack of knowledge about access to health services, disparate access to information on pediatric conditions, language barriers, time schedules, or other barriers. [START_REF] Buron | Hospital emergency department utilisation rates among the immigrant population in Barcelona, Spain[END_REF] Lack in social support may also restrict the selection for day surgery procedures.

In the next few years the non-Italian pediatric population is expected to steadily increase; addressing disparities in the delivery of healthcare emerges as a core issue of public health that cannot be delayed.

children aged 1 -

 1 5 years and excluded newborns and infants aged < 1 year. Crude hospitalization rates per 1000 children-years by gender, citizenship, medical and surgical Diagnosis Related Groups-DRGs were computed. Since immigrants are more represented among younger children, hospitalization rate among immigrant and Italian children were compared by means of agestandardized rate ratios-RRs with 95% Confidence Intervals.

Table 1 .

 1 Hospitalization rates by Diagnosis-Related Group, gender and citizenship, and agestandardized rate ratios of immigrant versus Italian children.

		Crude Rate * 1000	Rate Ratio
	Diagnosis-Related Group	Immigrant Italians	(95% Confidence Interval)
	MALES
	All medical DRGs	66.7	70.1	0.92 (0.89 -0.96)
	All surgical DRGs	26.6	41.7	0.65 (0.62 -0.69)
	041-Extraocular procedures except orbit	1.4	2.0	0.67 (0.52 -0.87)
	060-Tonsillectomy/adenoidectomy	8.5	20.0	0.46 (0.41 -0.51)
	062-Miringotomy with tube insertion	0.4	1.4	0.34 (0.22 -0.54)
	163-Hernia procedures	2.3	3.0	0.74 (0.60 -0.91)
	340-Testes procedures for nonmalignancy	2.1	4.3	0.46 (0.38 -0.57)
	341-Penis procedures	1.3	1.9	0.69 (0.53 -0.91)
	343-Circumcision	4.1	1.1	3.68 (3.07 -4.41)
	Other surgical DRGs	6.6	7.9	0.85 (0.75 -0.96)
	FEMALES
	All medical DRGs	58.7	55.9	1.02 (0.98 -1.06)
	All surgical DRGs	13.1	25.9	0.53 (0.49 -0.58)
	041-Extraocular procedures except orbit	0.9	2.0	0.47 (0.34 -0.65)
	060-Tonsillectomy/adenoidectomy	6.0	15.1	0.44 (0.38 -0.49)
	062-Miringotomy with tube insertion	0.2	1.0	0.19 (0.09 -0.40)
	163-Hernia procedures	1.2	1.4	0.90 (0.67 -1.20)
	Other surgical DRGs	4.8	6.4	0.75 (0.65 -0.87)

ACKNOWLEDGMENTS

Dr Fedeli had primary responsibility for study design and drafting the manuscript. Dr Alba and dr Avossa performed analyses and revised the manuscript Dr Zambon and dr Spolaore participated in study design, interpretation of data and drafting the manuscript

FUNDING

None.

COPYRIGHT LICENCE STATEMENT

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd, and its Licensees to permit this article (if accepted) to be published in the Journal of Epidemiology and Community Health and any other BMJPGL products and to exploit all subsidiary rights, as set out in our licence.

COMPETING INTERESTS

None.


Sally Macintyre
email: sally@sphsu.mrc.ac.uk

Keywords: Archie Cochrane, randomised controlled trials, objections to trials, social and public health interventions, lack of evidence

Good intentions and received wisdom are not good enough: the need for controlled trials in public health.

3 Good intentions and received wisdom are not good enough: the need for controlled trials in public health.

Introduction: Cochrane and maternity care Archie Cochrane's book, 'Effectiveness and efficiency: random reflections on health services', [START_REF] Cochrane | Effectiveness and Efficiency: Random Reflections on Health Services[END_REF] is well known for arguing the case for randomised controlled trials (RCTs) in health care. Antenatal care was one of the fields he singled out: 'this service is basically a multiphasic screening procedure, which by some curious chance, has escaped the critical assessment to which most screening procedures have been subjected in the last few years and there seems no reason why the same approach that has proved so useful elsewhere should not be used here'. [1 p.66] I was particularly interested in this comment because at the time I was involved in evaluating a modified schedule of antenatal care, using a before and after, case study, approach. [START_REF] Hall | Antenatal Care Assessed: a Case Study of an Innovation in Aberdeen[END_REF] Our problem was that there was no clear counterfactual with which to compare the new system. The study, which cost a not insignificant amount, was therefore somewhat inconclusive, other than finding that the new system did not seem to be a complete disaster or kill mothers and babies. Opponents could use our findings to suggest the new system was worse, and supporters that it was better, than the old one. We noted that: 'Random allocation to different schedules would have maximised comparability between experimental and control groups, and simultaneous comparisons would have avoided the contaminating effects of secular change on the outcome measures used'. [2 p.115] The arguments against using an RCT were that it was unethical to experiment on pregnant women and their children, and that antenatal care was a complex matter and therefore inherently unsuitable for an RCT. Interestingly, it was considered ethically permissible to experiment in a non-randomised way, in the process withholding what was currently considered normal care from pregnant women, and scientifically permissible to introduce and try to evaluate a complex system of care without any controls. Subsequently, Cochrane's arguments were highly influential among perinatal epidemiologists, and a number of RCTs of maternity care in the UK were undertaken, including:

•

Midwife or GP led care versus obstetrician led care [START_REF] Hundley | Midwife managed delivery unit: a randomised controlled comparison with consultant led care[END_REF][START_REF] Tucker | Should obstetricians see women with normal pregnancies? A multicentre randomised controlled trial of routine antenatal care by general practitioners and midwives compared with shared care led by obstetricians[END_REF][START_REF] Turnbull | Randomised, controlled trial of efficacy of midwife-managed care[END_REF] • Traditional versus reduced schedules of antenatal visits [START_REF] Sikorski | A randomised controlled trial comparing two schedules of antenatal visits: the antenatal care project[END_REF] • Women holding or not holding their own obstetric records [START_REF] Elbourne | The Newbury maternity care study: a randomised controlled trial to assess a policy of women holding their own obstetric records[END_REF] • Perineal management (restrictive versus liberal use of episiotomy) [START_REF] Sleep | West Berkshire perineal management trial[END_REF] • Enema on admission [START_REF] Romney | Is your enema really necessary?[END_REF][START_REF] Drayton | They know what they're doing[END_REF] • Postnatal support for mothers in disadvantaged inner-city areas.

[11]

Many of these trials were initially thought to be impossible, unethical and/or impractical, but they nevertheless happened. They had a number of important features. Firstly, they did not insist on slavish adherence to a standardized protocol. The trials of midwife versus shared care did not involve women being banned from seeing obstetricians or midwives, but rather the comparison of two general policies or principles [START_REF] Tucker | Should obstetricians see women with normal pregnancies? A multicentre randomised controlled trial of routine antenal care by general practitioners and midwives compared with shared care led by obstetricians[END_REF]. Secondly, they involved multiple components and series of decisions, social interactions and behaviours. Thirdly, many evaluated activities spanning many months. Fourthly, they involved multiple outcomes as well as multiple inputs (e.g., the antenatal care trials typically looked at antenatal admissions, non-attendances, numbers of antenatal visits, antenatal diagnoses, inductions of labour, satisfaction with care, etc). Fifthly, they involved evaluations of processes and acceptability as well as outcomes.

Sixthly, randomisation meant that results were less likely to be biased by self-selection of patients or professionals, and were therefore more conclusive than previous case study approaches. However these (fairly typical) characteristics of healthcare RCTs often seem to be misunderstood by opponents of public health RCTs.

Public health research

From the late 1990s a number of commentaries in the UK pointed to the lack of robust evidence to support social and public health policies in the UK. [START_REF] Macintyre | Using evidence to inform health policy: case study[END_REF][START_REF] Milward | Public Health Intervention research: the evidence[END_REF] One report noted:

'Although there is often evidence on the scientific justification for action and for some specific interventions, there is generally little evidence about the cost-effectiveness of public health and preventative policies or their practical implementation' [15 p.5] Why so little evidence? In the UK, many evaluations focus on inputs, throughputs and customer or professional satisfaction rather than on outcomes. Secondly, few policies or programmes are implemented in ways which facilitate robust evaluation of outcomes (for example they often lack baseline data, comparison groups, clear objectives, and/or statistical power). Thirdly, there is a general reluctance in the UK to subject social or public health policies to RCTs. There have been far fewer controlled studies in the UK than in the USA, which raises issues of generalisability across contexts (for example the 'nurse family partnership' developed and extensively studied in the USA [START_REF] Olds | Effects of Nurse Home Visiting on Maternal and Child Functioning: Age-9 Follow-up of a Randomized Trial[END_REF] may not be relevant in the UK where deprived first-time mothers already have access to antenatal and postnatal support via the NHS). These issues together militate against the production of robust evidence about effectiveness and efficiency.

Recently in the UK, members of parliament criticised policymakers' approaches to evaluation:

'All too often Governments rush in with insufficient thought, do not collect adequate data at the beginning about the health of the population which will be affected by the policies, do not have clear objectives, make numerous changes to the policy and its objectives and do not maintain the policy long enough to know whether it has worked ' [17 p.5] They were particularly critical of officials' reactions to suggestions that controlled trials should be used. Many of these responses suggested fundamental misunderstandings about the principles and practice of RCTs.

For example, one senior civil servant rejected suggestions that a 'Healthy Towns' initiative be subjected to a controlled trial by saying:

'it would challenge any academic to come up with a randomised town' [18 p. 7],

implying that randomisation means choosing one town at random and treating it as representative of all towns. In the next section I illustrate and discuss such common misconceptions, in particular that community trials are essentially different from health care trials.

Some objections to RCTs in public health One reason for objections to RCTs of public health policies or programmes is the belief that, unlike surgical or pharmaceutical interventions, they are unlikely to do harm. This view privileges social and public health actions, and assumes that the plausibility of potential benefit is a sufficient basis for action [START_REF] Skrabanek | Why is preventive medicine exempted from ethical constraints?[END_REF].

However, there are numerous examples of apparently plausible policies or programmes having no benefit or actually being harmful. For example, in the UK the risk of death from fire is associated with low socio-economic status because of social differences in risk factors for fires and ownership of smoke alarms, and the risk of death in a house fire is three times higher in homes without smoke alarms; so it is plausible that giving free fire alarms to deprived households might reduce excess fire deaths among them. However, an RCT found that giving out free alarms in a deprived community did not reduce injuries from fire, because few alarms had been installed or maintained. It concluded that issuing free smoke alarms may waste resources and be of little benefit unless alarm installation and maintenance is assured. [START_REF] Diguiseppi | Incidence of fires and related injuries after giving out free smoke alarms: cluster randomised controlled trial[END_REF] The Scared Straight programme in the USA brings juvenile delinquents into prisons to meet life prisoners, who attempt to deter them from a life of crime. Criminologists and many stakeholders, including the general public, have been positive about the programme, which has prima facie plausibility. However none of seven randomised controlled trials showed any benefit, and a meta-analysis showed that recidivism rates were higher among the experimental group. [START_REF] Petrosino | Scared Straight' and other juvenile awareness programs for preventing juvenile delinquency[END_REF] If there had not been RCTS of fire alarms and Scared Straight, we might continue to implement these programmes on the basis of their plausibility.

Community trials are impossible.

It is often simply stated as a matter of agreed fact that RCTs are impossible in community settings. However a wide range of communitybased RCTs have already been undertaken or planned, including:

•

The Mexican universal health insurance programme [START_REF] King | Public policy for the poor? A randomised assessment of the Mexican universal health insurance programme[END_REF] •

The effects of hand washing on child health in squatter settlements in Karachi [START_REF] Luby | Effect of handwashing on child health: a randomised controlled trial[END_REF] •

The deterrent effect of police raids on crack houses [START_REF] Sherman | Deterrent effects of police raids on crack houses: a randomized, controlled experiment[END_REF] •

The effectiveness of toughened glassware in reducing injuries in bars [START_REF] Warburton | Effectiveness of toughened glassware in terms of reducing injury in bars: a randomised controlled trial[END_REF] • School breakfast clubs [START_REF] Shemilt | A national evaluation of school breakfast clubs: evidence from a cluster randomized controlled trial and an observational analysis[END_REF] • Out-of-home day care for disadvantaged families [START_REF] Toroyan | Effectiveness of out-ofhome day care for disadvantaged families: randomised controlled trial[END_REF] • Community level interventions to address social and structural determinants of health in 40 areas in London [START_REF] Wall | Evaluation of community level interventions to address social and structural determinants of health: a cluster randomised controlled trial[END_REF] 5. Public health trials are more difficult than health care trials.

Some opponents of public health RCTs seem to assume that RCTs in health care are easy to set up and do not involve problematic ethical issues (in contrast to what is required for community-based trials).

However similar difficulties have been overcome in health care RCTs; for example, for temporal lobe epilepsy, [START_REF] Wiebe | A randomized controlled trial of surgery for temporal-lobe epilepsy[END_REF] arthroscopic surgery for osteoarthritis of the knee, [START_REF] Moseley | A controlled trial of arthroscopic surgery for osteoarthritis of the knee[END_REF] and transplantation of embryonic dopamine neurons for severe Parkinson's disease [START_REF] Freed | Transplantation of Embryonic Dopamine Neurons for Severe Parkinson's Disease[END_REF] (the latter two involving sham surgery in the control group). The trialists surmounted many of the difficulties often regarded as too difficult in community evaluations.

6. RCTs require one to adhere strictly to protocol.

One objection to public health RCTs is that they force one to stick rigidly to protocol:

'A population outcome is the goal. Such a broad focus means that strict control of intervention, subject and analysis required for a true experiment or clinical trial is impossible. This send shudders down the spines of those brought up in the empirical tradition.' [19 p.2] However, healthcare RCTs do not require one to have such strict standardisation. The trial of perineal management did not insist that women in the experimental arm all had episiotomies and nobody in the control arm did, [START_REF] Sleep | West Berkshire perineal management trial[END_REF] and the RCT of surgical versus medical treatment for epilepsy did not closely control what the surgical or medical treatments were. [START_REF] Wiebe | A randomized controlled trial of surgery for temporal-lobe epilepsy[END_REF] Intention-to-treat analysis of trial outcomes is recommended precisely because not everyone in the intervention group will actually receive the intervention or receive it in the same way, and that not everyone in the control group will be deprived of the intervention. [START_REF] Newell | Intention-to-Treat Analysis: Implications for Quantitative and Qualitative Research[END_REF] The term 'controlled' may lead to some confusion here, it sometimes being interpreted as meaning rigid fidelity to the programme, rather than some sort of comparison with a counterfactual such as a comparison group, i.e. what would happen if the intervention had not taken place.

7. RCTs involve a single experimental and comparison unit.

'Even where matching populations have been found, a final comparison comes down to a single case with control design and a critical reviewer can easily dismiss results' [19 p.3] This seems to assume that public health RCTs would only select one intervention and one comparison group (see the earlier comment about 'a random town' [START_REF]Oral evidence taken before the health committee Wednesday 19th of November 2008[END_REF]); however as has been pointed out:

'It is common to see reports of community intervention trials in which one intervention community is compared with one control committee. This is equivalent to a clinical trial with one patient in each treatment group. [37 p.323] A key element of healthcare RCTs is that they involve sufficient numbers in both experimental and control group to rule out the role of chance, and in many cases in public health it would similarly be possible to have sufficient numbers of experimental and control units (for example, schools, neighbourhoods or towns). [START_REF] Hayes | Simple sample size calculations for cluster randomised trials[END_REF] 8. RCTs are expensive, and if they do not demonstrate a positive difference are failures.

'There are examples of failed, expensive trials. For example no intervention effect was observed among heavy smokers, the primary target population of the COMMIT trial. Similarly CART demonstrated limited positive results, with most cancer related behaviour showing no intervention effects…' [38 p.158] This seems to conflate the notion of a failed trial (i.e. one that is badly designed or fails to recruit sufficient numbers) with a failed policy or intervention (i.e. one that shows modest or no benefit or actual harm).

Both the fire alarm [START_REF] Diguiseppi | Incidence of fires and related injuries after giving out free smoke alarms: cluster randomised controlled trial[END_REF] and the Scared Straight trials [START_REF] Petrosino | Scared Straight' and other juvenile awareness programs for preventing juvenile delinquency[END_REF] illustrate that RCTs can be successful and cost effective even if they show reasonably conclusively that an intervention has no, modest, or adverse effects. 9. RCTs do not have long enough follow-up.

'In population health research many outcomes of interest are far into the future … the practical difficulties in maintaining prospective randomisation for prolonged periods across entire populations are substantial' [38 p.157] However there is no intrinsic reason for the issue of length of follow-up to be any different between an RCT and an uncontrolled evaluation. (The High Scope Perry RCT of early childhood intervention has now followed up the participants for 40 years [START_REF] Schweinhart | Lifetime effects: The High/Scope Perry Preschool study through age 40 Ypsilanti[END_REF]) Such comments may be confusing the long-term follow-up of outcomes with the long-term maintenance of the exposure to which people or communities were randomised.

10. RCTs have poor external validity.

'a disadvantage to using RCTs in population health research is the lack of generalisability, or low external validity' [39 p.157] It is difficult to understand why non RCTs in community settings, for example the numerous (and sometimes very expensive) non-randomised evaluations in the UK of area based initiatives such as Sure Start [START_REF] Belsky | Effects of Sure Start local programmes on children and families: early findings from a quasi-experimental, cross sectional study[END_REF] or Health Action Zones [START_REF] Barnes | Health Action Zones: partnerships for health equity[END_REF] should be regarded as any more generaliseable than RCTs.

11. RCTs are unethical.

It is often seen as unethical to conduct policy RCTs because they withhold potential benefits from the control group. [START_REF] Skrabanek | Why is preventive medicine exempted from ethical constraints?[END_REF] However this assumes that well intentioned policies will be beneficial, and that the direct or opportunity costs of implementing a policy are of no ethical concern. As was pointed out in the early days of healthcare RCTs, it seems perverse to see it as ethical to give or withhold programmes of unknown benefit to 100% of the population, but not to 50%. [START_REF] Smithells | Iatrogenic hazards and their effects[END_REF][START_REF] Chalmers | Trying to do more good than harm in policy and practice: the role of rigorous, transparent, up-to-date, replicable evaluations[END_REF] This is particularly the case when the intervention has to be rationed anyway (e.g. not every community can have a Sure Start Local Programme or be a Health Action Zone).

As members of Parliament have pointed out:

'All the reforms we have discussed are experiments on the public and can be as damaging (in terms of unintended effects and opportunity cost) as unevaluated new drugs or surgical procedures.

Such wanton large-scale experimentation is unethical, and needs to be superseded by more rigid rigorous culture of piloting, evaluating and using the results to inform policy.' [17 p.66]

Conclusion

It appears that many objections to social and public health RCTs are based on false comparisons with healthcare RCTs, the latter being seen to be simple, and to have standardised exposures and outcomes. Many of these objections were raised earlier about healthcare RCTs, but have been overcome in the healthcare arena, often with considerable ingenuity, and with recognition of the complexity of human beings and their contexts.

Do objections to social and public health RCTs matter? I believe they do, and that Cochrane would agree. For example, the government refused to allow a randomised evaluation of the Sure Start programme in England, which has led to considerable problems in interpreting the results, since although the researchers tried to find matching areas not receiving the intervention, and to control for any obvious socio-economic and demographic differences between intervention and control areas, differences between areas receiving and not receiving the intervention, rather than the intervention itself, may influence any observed differences in outcome [17] [44]. The results of an expensive evaluation of an expensive intervention can therefore be contestable rather than conclusive.

With rare exceptions, such as when a new universal policy such as banning smokeless fuel or indoor smoking is introduced and can be evaluated using interrupted time-series methods, [START_REF] Craig | Developing and evaluating complex interventions: new guidance[END_REF] RCTs are both more possible than many objectors think, and more conclusive about the benefits and cost effectiveness of (usually publicly funded) policies and interventions.

So I think we should be braver and much more creative in arguing (or non exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in JECH and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence (http://jech.bmj.com/site/about/licence.pdf).

(

  whether with politicians, public health practitioners, research funders, potential recipients or ethics committees) for RCTs. As for the privileging of social and public health as not requiring robust randomised evidence, I believe that Cochrane's comments about psychiatry are equally applicable to public health: 'I cannot agree that colleagues, however distinguished, intelligent and hard-working, and who obviously believe they are doing good, should have a blank cheque to encourage the use of (XX) without bothering to measure the benefit and cost of what they are doing'[1 p.59]

Acknowledgements

This is an abridged version of the Cochrane lecture given at the Society for Social Medicine annual conference in 2009. I am grateful to Lyndal Bond, Iain Chalmers, Matt Egan, Mark Petticrew and Helen Roberts for their contributions to my thinking on this topic, in some cases over many years, and to the Society for Social Medicine committee for inviting me to give this lecture. My work is supported by the UK Medical Research Council, wbs U.1300.00.006.

Competing interests: none declared


PhD Maria Cotelli
email: mcotelli@fatebenefratelli.it

Marco Calabria

Rosa Manenti

Sandra Rosini

Orazio Zanetti

Stefano F Cappa

Carlo Miniussi

Improved language performance in Alzheimer disease following brain stimulation

Keywords: Neurorehabilitation, rTMS, sentence comprehension, language, transcranial magnetic stimulation

come   L'archive ouverte pluridisciplinaire

Introduction

Alzheimer's Disease (AD) is a progressive disorder that impacts memory, language and several other cognitive functions. Given the limited effectiveness of pharmacological treatments, non-pharmacological interventions in AD have gained attention in recent years, and there are currently many different approaches under study, ranging from multistrategy approaches to cognitive training [START_REF] Cotelli | Cognitive rehabilitation in Alzheimer's disease[END_REF] .

Despite the potential therapeutic impact of the non-pharmacological approaches, the neural mechanisms underlying the beneficial effects of behavioral interventions remain largely unknown. Functional neuroimaging studies have shown that rehabilitation in patients with developmental and acquired cerebral damage may lead to functional cortical reorganization, a process mediated by activity-dependent plasticity mechanisms [START_REF] Warburton | Mechanisms of recovery from aphasia: evidence from positron emission tomography studies[END_REF] . These "plastic" mechanisms may also play a role in the aging brain and in AD [START_REF] Buckner | Memory and executive function in aging and AD: multiple factors that cause decline and reserve factors that compensate[END_REF] .

In recent years, new techniques for studying the human brain that allow for the noninvasive neurostimulation have emerged. Repetitive Transcranial Magnetic Stimulation (rTMS) is a technique that delivers several magnetic pulses in rapid sequence up to frequencies of 100Hz. rTMS can modulate neuronal activity, with the exact effects depending on the stimulation frequency (i.e., ≤1Hz stimulation results in inhibition, while ≥5Hz stimulation mostly leads to excitation). There have been no studies to date that have explored the long-term effects of rhythmic off-line rTMS in AD patients. Therefore, the main purpose of the present study was to investigate whether the application of highfrequency rhythmic rTMS, for 2 or 4 weeks, to the left dorsolateral prefrontal cortex (DLPFC) resulted in cognitive improvements [START_REF] Miniussi | Efficacy of repetitive transcranial magnetic stimulation/transcranial direct current stimulation in cognitive neurorehabilitation[END_REF] in patients with AD. More specifically, we hypothesized that this type of stimulation may lead to improved language performance i.e., production and/or comprehension. Such prediction comes from a previous work on naming in AD patients [START_REF] Cotelli | Effect of transcranial magnetic stimulation on action naming in patients with Alzheimer disease[END_REF][START_REF] Cotelli | Transcranial magnetic stimulation improves naming in Alzheimer disease patients at different stages of cognitive decline[END_REF] . A possible effect on sentence comprehension was predicted on the basis of a study in young normal subjects [START_REF] Manenti | The role of the prefrontal cortex in sentence comprehension: an rTMS study[END_REF] , which provided direct evidence of DLPFC involvement in sentence comprehension.

In addition, an important goal of the present study was to verify whether the cognitive benefits, previously recorded solely during on-line rTMS, might persist after the end of the stimulation. We adopted a multiple-baseline design, comparing the stimulation effects with a placebo condition (sham-stimulation) during the first two weeks of treatment. This phase was followed by two weeks of rTMS stimulation in all patients, in order to evaluate whether a longer rTMS application (four vs. two weeks) would further improve the expected benefits in the patient's performance. Finally, we assessed the persistence of the effects eight weeks after the end of the treatment (Figure 1).

Subjects and Methods

Participants

Outpatients (n=10) diagnosed as having probable moderate AD, according to the NINCDS-ADRDA 8 criteria, were enrolled.

Patients with potentially confounding neurological and psychiatric disorders, epilepsy clinically recorded hearing or vision impairment, or with a history of alcohol abuse, psychosis or major depression were not included in the study. All patients had been on a stable dose of cholinesterase inhibitor (donepezil or rivastigmine) for at least six months prior to the onset of the study. The use of drugs with anticolinergic properties was used as an exclusion criterion. rTMS Patients were randomly assigned to one of the two groups: i) Real-Real group (RR), in which the patients received four weeks of rTMS stimulation of the DLPFC; ii) Placebo-Real group (PR), in which patients received DLPFC placebo stimulation during the first two weeks followed by two weeks of real stimulation (Figure 1A). Each week of rTMS treatment consisted of 5 sessions (25 minutes each, one per day). rTMS was delivered by a Magstim unit featuring a double 70mm cooled coil. Before starting the rTMS treatment, the motor excitability stimulation threshold was established for each subject (51.56 ±5.9%).

The stimulation intensity used during the experiment was set to 100% of each subject's motor threshold. Trains of rhythmic high-frequency (20Hz) rTMS were delivered in short periods (2sec-duration) separated by longer periods (28sec) of no stimulation, for each daily session. The total number of pulses for each session was 2000 (40 stimuli/train, 50 trains). These parameters are consistent with safety recommendations for rTMS [START_REF] Rossi | Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research[END_REF] .

Furthermore, all participants tolerated rTMS well and did not report any adverse effects. In the placebo condition, a sham coil was used [START_REF] Rossi | A real electro-magnetic placebo (REMP) device for sham transcranial magnetic stimulation (TMS)[END_REF] .

Figure-1

We localized the target areas using the SofTaxic neuronavigator system (www.emsmedical.net) on an MRI template. Based on these estimated MRIs, the average location of the stimulating points was centered on Talairach coordinates X=-35, Y=24, Z=48, corresponding to the DLPFC (Brodmann Area 8/9). We chose to stimulate this area based on the results of previous experiments [START_REF] Cappa | The role of the left frontal lobe in action naming: rTMS evidence[END_REF][START_REF] Cotelli | Effect of transcranial magnetic stimulation on action naming in patients with Alzheimer disease[END_REF][START_REF] Cotelli | Transcranial magnetic stimulation improves naming in Alzheimer disease patients at different stages of cognitive decline[END_REF][START_REF] Manenti | The role of the prefrontal cortex in sentence comprehension: an rTMS study[END_REF] . To stimulate the DLPFC, the coil was placed with the junction of the two coil wings above the target point. During the experiment the coil was fixed by means of a mechanical support.

Cognitive Assessment

Standard cognitive assessment was divided into two sessions. Neuropsychological testing was administered by an experienced examiner who was blind to patient treatment allocations. The cognitive assessment included tests to screen for dementia, together with neuropsychological tests for memory, executive functions and language. The results of the cognitive assessments at baseline, before rTMS treatment, and at two weeks (T2) are reported in Table 1 for both experimental groups. Moreover, we performed the same detailed cognitive assessment four weeks (T4) and 12 weeks (T12) after the onset of the rTMS treatment (note that T12 corresponds to 8 weeks after the end of the treatment). All the tests were administered and scored according to standard procedures [START_REF] Miceli | Batteria per l'Analisi dei Deficit Afasici[END_REF][START_REF] Lezak | Neuropsychological Assessment[END_REF] Table 1

Statistical analysis

Demographic variables (age and education) of the two groups were compared at baseline, using parametric analyses (paired t-test). A p-value<0.05 was considered significant.

The behavioral effects induced by the rTMS protocol after two weeks of daily stimulation were assessed using a mixed-model ANOVA, considering group (Real-Real vs. Placebo-Real) as a between-subject factor, and time (baseline vs. two weeks) as a withinsubject factor. Further analysis was performed to assess the long-term efficacy of rTMS treatment using four time instants (Baseline vs. two weeks, four weeks and 12 weeks) as a within-subject factor.

Results

We identified no significant differences in the demographic variables between groups (Table 1, p>0.05).

To verify the presence of short-term behavioral effects induced by rTMS, we compared the performance of both groups at baseline and at the two-week evaluation. A significant difference between groups was found in terms of the percentage of correct responses only in auditory sentence comprehension subtest from the Battery for Analysis of Aphasic Deficits (SC-BADA) over time [group x time interaction: F(1, 8)=6.07, p=.04; η p 2 =.43]. The Real-Real group improved its performance (p=.008) at two weeks (77.3 ±6.5) with respect to baseline (66.6 ±8.6), whereas the Placebo-Real group showed no significant differences (p=.99) between baseline (66.0 ±7.1) and two weeks of placebo rTMS (65.9, ±9.6).

We further analyzed SC-BADA scores at baseline, two, four, and 12 weeks to assess the long-term efficacy of rTMS in both groups. A significant main effect of time [F(3, 24)=3.87, p=.02] was found. Post-hoc analysis, Bonferroni, showed that the percentage of correct responses in SC-BADA at 12 weeks (77.2 ±2.7) was still significantly different (p=.02) from baseline (66.3 ±7.45) (Figure 1B). No significant differences were found for other language abilities, nor for other cognitive functions (such as cognitive estimation and memory). See Table 1 for more details.

Discussion

The main purpose of this study was to investigate whether the application of highfrequency rTMS to the left DLPFC for 25 min a day, five days a week, for two weeks may lead to significant cognitive improvements in patients with AD. Specifically, we hypothesized that this protocol would result in changes in language performance, i.e., facilitation of language production and/or comprehension. In addition, we compared the effects of two or four weeks of stimulation to evaluate whether a longer rTMS application would result in a greater and/or longer-lasting effect. Finally, another important aim of the present study was to verify whether the cognitive benefits recorded immediately after rTMS treatment would persist eight weeks after the end of the treatment protocol (T12).

Overall, the results of our study show a significant effect of rTMS treatment on auditory sentence comprehension.

In contrast with our previous studies [START_REF] Cotelli | Effect of transcranial magnetic stimulation on action naming in patients with Alzheimer disease[END_REF][START_REF] Cotelli | Transcranial magnetic stimulation improves naming in Alzheimer disease patients at different stages of cognitive decline[END_REF] , in the present study we failed to observe a significant effect on naming performance in AD. These results may be attributed to the rTMS paradigm used (off-line vs. on-line) with a short term facilitation, in our previous study, strictly related to the timing of stimulation (i.e., few millisecond before the naming).

In the present study we applied an off-line rTMS approach in which patients received daily rTMS treatment, while in the previous studies rTMS was applied to DLPFC during the execution of the naming task.

We also found that the administration of rTMS for four weeks did not result in additional improvements in performance compared to the application of rTMS for two weeks. A meta-analysis by the Cochrane Collaboration 14 concluded that rTMS significantly improves depression only after a minimum of two weeks of treatment. Our results suggest that two weeks of rTMS is also sufficient to evidence behavioral improvements in AD patients.

As regards the long-term effects, we identified an improvement in sentence comprehension eight weeks (T12) after the end of the rTMS intervention. To date, this is the first study that shows a long-lasting cognitive effect of rTMS treatments in AD patients.

Another important result of our study was the absence of any rTMS effects on memory and executive functions suggesting that learning effects cannot explain data.

Therefore, the facilitation effect of DLPFC rTMS in AD appears to be specific to the language domain rather than reflecting a general, non-specific effect on cognitive processing.

Why did rTMS induce this improvement in patient language performance? The neurophysiological mechanisms responsible for rTMS-induced facilitation remain unknown. A number of investigations suggest that rhythmic transcranial stimulation can exert positive effects on cognitive performance [START_REF] Miniussi | Efficacy of repetitive transcranial magnetic stimulation/transcranial direct current stimulation in cognitive neurorehabilitation[END_REF] . A possibility is that the modification of cortical activity through the use of rhythmic stimulation may re-adjust pathological patterns

Figure 1 .

 1 Figure 1.

Table 1 .

 1 Demographic and neuropsychological data. * = p<.05

	REAL-REAL (n= 5)	PLACEBO-REAL (n=5)	Group Time	Time x Group	REAL-REAL (n= 5)	PLACEBO-REAL (n=5)	Group Time	Time x Group
			P-value			P-value

Acknowledgement

We wish to thank patients and caregivers for their patience. This research was supported by a Project grant from the "Ministero della Sanità" and from Associazione Fatebenefratelli per la Ricerca (AFaR).

within the affected functional networks [START_REF] Thut | New insights into rhythmic brain activity from TMS-EEG studies[END_REF] .

The present findings may reflect an rTMS-induced modulation of short and/or longrange cortical synaptic efficacy and connectivity that potentiates the system within the language network, leading to more effective processing.

The present preliminary results highlight the therapeutic potential of the induction of long-term neuromodulatory effects using brain stimulation. They hold considerable promise, not only for advancing our understanding of brain plasticity mechanisms, but also for designing new rehabilitation strategies in patients with neurodegenerative disease.


Jerzy Wieslaw

Mariusz Cubala
email: cubala@gumed.edu.pl

Anna Wiglusz

Maria Burkiewicz

Jerzy Wiesław

M.D Cubała

Ph.D. § , Mariusz Wiglusz M.D Anna Burkiewicz

PhD Maria Gałuszko- Węgielnik

Keywords: zolpidem, sex, pharmacokinetics, CYP3A

come     Zolpidem pharmacokinetics and pharmacodynamics in metabolic interactions involving CYP3A: sex as a differentiating factor

based inactivator of human CYP3A in vitro with the assessment of its metabolic interaction potential with CYP3A drugs [START_REF] Polasek | In vitro-in vivo extrapolation of zolpidem as a perpetrator of metabolic interactions involving CYP3A[END_REF]. The paper clearly points out the mechanism of inactivation of human CYP3A in vitro along with its implications for the in vivo metabolic interactions involving CYP3A. The issue is of vital importance due to the prescription rate of zolpidem with regard to efficacy and patients' safety.

However, the discussion of that interesting paper left unaddressed an issue of patients' sex with its endocrine specificity as if zolpidem pharmacokinetics were independents of the one. The pharmacokinetics of zolpidem seems to be related to the endocrine factors associated with CYP3A4 metabolism. Low plasma concentrations of free testosterone may contribute to lower CYP3A activity and women achieve up to 50% higher zolpidem plasma levels while the exposure to testosterone activates the biotransformation via CYP3A [START_REF] Olubodun | Pharmacokinetic properties of zolpidem in elderly and young adults: possible modulation by testosterone in men[END_REF]. That effect is conspicuous in the relative higher incidence of ADR with zolpidem in women [START_REF] Cubała | Zolpidem abuse, dependence and withdrawal syndrome: sex as susceptibility factor for adverse effects[END_REF].

The conclusions of the paper are true for the model study on male subjects. The discussion, however, might include the exciting element of endocrine-related differences in zolpidem action.

  Zolpidem pharmacokinetics and pharmacodynamics in metabolic interactions involving CYP3A: sex as differentiating factorJournal: European Journal of Clinical PharmacologyManuscript ID: EJCP-2010-0164

  We read with interest the paper by Polasek et al. on the evaluation of zolpidem as a mechanism-

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	Type of submission: Letter Date Submitted by the Author: 03-May-2010 Gałuszko-Węgielnik, Maria; Medical University of Gdańsk, Dept. of of Psychiatry Psychiatry F o r P e e r R e v i e w o r P e e r R e v i e 59 F 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 w

Complete List of Authors: Cubała, Wiesław; Medical University of Gdańsk, Dept. of Psychiatry Wiglusz, Mariusz; Medical University of Gdańsk, Dept. of Psychiatry Burkiewicz, Anna; Medical University of Gdańsk, Dept.

Conflict of interest statement

The authors declare that they have no conflict of interest.