Dearbhla M Kelly

MD Hans-Joachim Anders

PhD Aminu K Bello

Gabriel Choukroun

MD Rosanna Coppo

MD Gavin Dreyer

MD Kai-Uwe Eckardt

PhD David W Johnson

PhD Vivekanand Jha

MD David C H Harris

Dearbhla M Kelly Mbbch

Wolfson

MD Adeera Levin

MSc Meaghan Lunney

PhD Valerie Luyckx

MD Hans-Peter Marti

MD Piergiorgio Messa

MD Thomas F Mueller

Syed Saad Bsc

PhD Benedicte Stengel

PhD Raymond C Vanholder

MD Talia Weinstein

Maryam Khan

PhD Deenaz Zaidi

MD Mohamed A Osman

MSc Feng Ye

MD Marcello Tonelli

PhD Ikechi G Okpechi

Prof Eric Rondeau
email: eric.rondeau@aphp.fr

Kidney Health Atlas: structures, organization, and services for the management of kidney failure in Western Europe

Keywords: max 6): Kidney failure, end-stage kidney disease, Chronic kidney disease, Dialysis, Kidney transplantation, Kidney registries

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Compared to other world regions, Western Europe benefits from functional health care systems, established non-communicable disease guidelines, higher health professional density, high availability of essential medicines, and more widespread universal health coverage. [START_REF] Bello | Global Kidney Health Atlas: A report by the International Society of Nephrology on the current state of organization and structures for kidney care across the globe[END_REF][START_REF] Rondeau | Challenges and opportunities for nephrology in Western Europe[END_REF] In line with this infrastructure, there has been a decline in premature mortality from the four major types of non-communicable diseases (cardiovascular diseases, cancer, diabetes, and chronic respiratory diseases). [START_REF]More Than Numbers -Evidence for All[END_REF] However, large variability in mortality rates remain, both between sexes and between countries. One out of every 10 Europeans has chronic kidney disease (CKD); among contributing factors are the rising prevalence of diabetes and obesity, and dynamics associated with an aging population. [START_REF]Recommendations for sustainable kidney care[END_REF] In parallel with these changes, the prevalence of kidney replacement therapy (KRT; dialysis and kidney transplantation) is steadily growing and has led to an equally aging dialysis population. [START_REF] Pippias | The changing trends and outcomes in renal replacement therapy: data from the ERA-EDTA Registry[END_REF] Since 1964, the European Renal Association-European Dialysis and Transplant Association (ERA-EDTA) has collected data on KRT modalities such as dialysis and transplantation via national and regional kidney registries from 36 countries in Europe and has charted the evolution of kidney failure (KF) epidemiology through the publication of annual reports [START_REF] Kramer | Renal replacement therapy in Europe-a summary of the 2010 ERA-EDTA Registry Annual Report[END_REF][START_REF] Noordzij | Renal replacement therapy in Europe: a summary of the 2011 ERA-EDTA Registry Annual Report[END_REF][START_REF] Pippias | Renal replacement therapy in Europe: a summary of the 2012 ERA-EDTA Registry Annual Report[END_REF][START_REF] Kramer | Renal replacement therapy in Europe: a summary of the 2013 ERA-EDTA Registry Annual Report with a focus on diabetes mellitus[END_REF][START_REF] Kramer | The European Renal Association -European Dialysis and Transplant Association (ERA-EDTA) Registry Annual Report 2016: a summary[END_REF] and epidemiological trends. [START_REF] Van De Luijtgaarden | Trends in dialysis modality choice and related patient survival in the ERA-EDTA Registry over a 20-year period[END_REF] As one of the world's largest international registries of kidney care, it contributes substantially to enabling international comparisons.

In 2020, nephrology in Europe faces a number of new challenges in addition to the wellknown changes in population demographics with aging population and workforce challenges.

First and foremost, the global pandemic resulting from severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 virus (referred to as COVID- 19) has a number of far-reaching complications including high rates of acute kidney injury (AKI), [START_REF] Yang | Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study[END_REF] risk of transmission of infection among vulnerable in-center dialysis patients, and the suspension of transplant services to avoid additional immunosuppression at this time. [START_REF] Boyarsky | Early Impact of COVID-19 on Transplant Center Practices and Policies in the United States[END_REF] Secondly, the ongoing war and consequent population movement in Syria and elsewhere in the Middle East, Africa, and South America, have led to a rise in the number of refugees receiving KRT in European countries. [START_REF] Van Biesen | Renal replacement therapy for refugees with end-stage kidney disease: an international survey of the nephrological community[END_REF] In addition to ethical, financial, and legal implications, forced migration in this context may increase the diversity of kidney pathologies, physical and psychological comorbidities, and cultural nuances. Secondly, climate change may pose new problems, with an increasing number of heatwaves in Europe [START_REF]Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Core Writing Team[END_REF] and heat-related AKI as an important contributor to mortality in this setting. [START_REF] Conti | General and specific mortality among the elderly during the 2003 heat wave in Genoa (Italy)[END_REF] There is also a climate-driven risk of increased 'tropical' infections, for example, poleward shifts of Aedes-borne virus distributions (particularly dengue, chikungunya, and Zika), with their associated AKI morbidity. [START_REF] Ryan | Global expansion and redistribution of Aedes-borne virus transmission risk with climate change[END_REF] Unexpected extreme weather conditions can also disrupt critical infrastructure (e.g., power and water supplies, transportation, and telecommunication services) required to deliver dialysis services. [START_REF] Anderson | Missed dialysis sessions and hospitalization in hemodialysis patients after Hurricane Katrina[END_REF] Lastly, Brexit may have ramifications for patients with kidney disease in terms of reciprocal healthcare, the supply of medical consumables, organ sharing across the European Union (EU) countries participating in the Eurotransplant and healthcare in Northern Ireland, [START_REF] Kmietowicz | Brexit and kidney disease: five minutes with…Fiona Loud[END_REF] as well as for European research and recruitment more broadly. [START_REF] Kmietowicz | Brexit and kidney disease: five minutes with…Fiona Loud[END_REF] Though it is likely that in the short-to-medium term, Brexit as a geopolitical issue will pale in comparison to the COVID-19 threat to globalization. With this landscape in mind, we use data from the second International Society of Nephrology Global Kidney Health Atlas (ISN-GKHA) survey to report on the availability, accessibility, affordability, and quality of KF care in Western Europe. However, we should emphasize that this is only a snapshot of disease burden in the region. The methodology for this research is described in detail elsewhere. [START_REF] Bello | Understanding distribution and variability in care organization and services for the management of kidney care across world regions[END_REF]

Results

Results of this study are presented in Tables and Figures and broadly summarized into two categories: desk research (Tables 12and Supplementary Table S1) and survey administration (Figures 2345and Supplementary Figures S1-S7).

Setting

Western Europe has had various historical (non-communist versus formerly communist countries), geographic, and economic (high-rather than middle/low-income countries) definitions in the past. However, for the purpose of this analysis, we used the ISN regional definition, which includes continental Europe (Austria, Belgium, France, Germany, Ireland, Liechtenstein, Luxembourg, the Netherlands, Switzerland, and the United Kingdom), Scandinavia (Denmark, Finland, Iceland, Norway, and Sweden), and Mediterranean Europe (Andorra, Greece, Israel, Italy, Malta, Monaco, Portugal, San Marino, Spain, and the Vatican). 21 This equated to a population of 433.7 million inhabitants living in predominantly industrialized, high-income countries. Germany (80.5 million), the United Kingdom (65.1 million), and France (67.4 million) are the most populous countries within Western Europe. 22 Western Europe is one of the wealthiest regions of the world and continues to experience economic growth, as evidenced by an increase in the gross national income (GNI) per capita from US$ 19,752 in 2000 to US$ 35,420 in 2018 and a total regional gross domestic product (GDP) of US$ 18.8 trillion, representing 22% of the global economy. 22 Accordingly, the average life expectancy at birth has increased progressively to 80.9 years. However, despite faring better than many other regions in the world, income inequality still exists in Western Europe. For example, the Gini index, a statistical measure of income equality whereby 0 represents perfect equality and 100 represents perfect inequality, is 36 in the United Kingdom, 34 in Spain, and 33 in Greece. 23 The EU Regional Human Development Index report also shows a clear northwest/southeast divide across EU regions for the overall index, which is a parameter composite of a country's life expectancy, education index, and GNI per capita. [START_REF] Hardeman | The EU Regional Human Development Index[END_REF] Within countries, differences exist among country regions as to performance in human development. This is especially the case for the United Kingdom, Spain, France, Italy, Germany, and Belgium. Capital city regions generally outperform noncapital city regions within countries.

Brief summary of the current state of kidney care in the region

The incidence of KF varies widely across Western European countries. According to the ERA-EDTA 2017 registry report based on data collected via national and regional kidney registries, the incidence of KRT for such patients in Europe was 127 per million population (pmp). [START_REF] Kramer | The European Renal Association -European Dialysis and Transplant Association (ERA-EDTA) Registry Annual Report 2016: a summary[END_REF] Within Western European countries, this ranged from 97 pmp in Switzerland to 252 pmp in Greece. Nearly two-thirds of patients were male with a mean age of 65.3 years, and diabetic nephropathy was the underlying etiology in 23% of cases. Hemodialysis (HD) was the most frequent modality at the start of KRT, followed by peritoneal dialysis (PD) and then pre-emptive kidney transplant. In the Western Europe region, the prevalence of KRT was 854 pmp, ranging from 760 pmp in Iceland to 1,965 pmp in Portugal. It has been proposed that varying socioeconomic factors, prevention programs, and real differences in CKD incidence may account for these differences. [START_REF] Heaf | Current trends in European renal epidemiology[END_REF]

Characteristics of participating countries

Forty-six respondents representing 21 of the 29 (72.4 %) countries in the ISN's Western Europe region completed the online questionnaire (Figure 1). The majority of respondents were nephrologists (n = 38, 85%), followed by policymakers (n = 4, 9%), other stakeholders (n = 2, 4%), non-nephrologist physicians (n = 1, 2%) and other health professionals (n = 1, 2%) with an overall response rate of 68.7%. Participating countries jointly represented a population of 433.1 million (99.9% of the total population in Western Europe). All participating countries were in the high-income category (n = 21, 100%), as were the eight territories that did not participate in the survey (Andorra, the Channel Islands, the Faroe Islands, Gibraltar, Greenland, the Isle of Man, Monaco, and San Marino). As a proportion of GDP, health expenditures in participating countries ranged from 12.1% in Switzerland to 6% in Luxembourg (Table 1). 26,27,[START_REF]GDP ranking[END_REF]

Burden of CKD and kidney failure in Western Europe

The average prevalence of CKD in Western Europe was 10.1% (95% CI: 9.6, 10.6), ranging from 7.84% in Israel to 11.84% in Sweden. The highest proportions of deaths and disability-adjusted life years (DALYs) attributed to CKD were found in Israel, Austria, and Greece (Supplementary Table S1).

Data on the prevalence of KF in Western Europe were available for all participating countries, with the exception of Liechtenstein and Malta. The median prevalence of treated KF in Western Europe was 1,038 pmp (interquartile range [IQR]: 948-1261), which is higher than the global median of 759 pmp. The countries with the highest prevalence were Portugal (1,612 pmp), Greece (1,319 pmp), and France (1,310 pmp) (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF] The median number of new cases of treated KF in the region (131 pmp; IQR: 113-177.5) was lower than the global median (142 pmp). Greece, Portugal, and Israel had the highest incidences of KF in Western Europe (252 pmp, 230 pmp, and 193 pmp respectively). In all Western European countries, HD was the most common dialysis modality (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF][START_REF] Jain | Global trends in rates of peritoneal dialysis[END_REF][START_REF]USRDS Annual Data Report: Epidemiology of kidney disease in the United States[END_REF] However, PD accounted for a significant proportion of dialysis treatment in Iceland, Sweden, and Denmark (23%, 22%, and 21%, respectively). Patients living with a functioning kidney transplant comprised approximately two-thirds of all treated KF patients in Norway, Iceland, and Netherlands (70.6%, 66.7%, and 63.8% respectively). The country with the lowest prevalence of KF patients living with kidney transplants was Greece (242.1 pmp; 18.4% of all KF patients) (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF]

Health finance and service delivery

In the vast majority of countries, costs of non-dialysis CKD and KRT care were covered by public funding (Figure 2). Services were free at the point of delivery with no outof-pocket costs for the patient in 67% of countries in Western Europe, compared to just 43% of countries around the world. Coverage of KRT costs by public funding (in whole or in part) was nearly universal in the region, with the exceptions of Germany and Liechtenstein, where part of the costs was covered by mandatory insurance.

Among the 21 participating countries, 18 (86%) had data available about the annual cost of dialysis. In the region, median annual costs (in USD) per person for maintenance HD ($60,037; IQR: $50,558-$77,040) and maintenance PD ($47,963; IQR: $30,248-$60,816) were well above global averages ($22,617 and $20,524, respectively) (Table 1). [START_REF] Van Der Tol | An International Analysis of Dialysis Services Reimbursement[END_REF] Data on the annual cost of kidney transplantation in the first year were available for 13 countries; costs per patient range from $27,971 in the United Kingdom to $114,220 in France. Patients in 14 countries (67%) paid no out-of-pocket costs for KRT, and patients in five countries (France, Iceland, Netherlands, Sweden, and Switzerland) covered 1-25% of these costs (Table 1). [START_REF] Van Der Tol | An International Analysis of Dialysis Services Reimbursement[END_REF] Fees were covered exclusively by private health insurance providers in Liechtenstein. A statutory health insurance model was used in Germany.

The organization and delivery of KF care was structured differently (no national framework) by regions in four countries (19%) and between adults and children in three countries (14%). In almost half of all countries, responsibility for KF care oversight rests with individual hospitals, trusts, or organizations (n = 10, 48%), followed by a national body (n = 7, 33%) and provincial or state level organizations (n = 7, 33%). Two countries (Germany and Liechtenstein) reported the organization and delivery of KF care as other.

Health workforce for nephrology care

Nephrologists are primarily responsible for KF care in Western Europe (n = 21, 100%), with some support from primary care physicians (n = 2, 10%) and nurse practitioners (n = 2, 10%) in some countries. The median number of nephrologists (22.9 pmp, IQR: 16.0-29.9) and the median number of nephrology trainees (5.9 pmp, IQR: 3.1-9.3) in Western Europe were much higher than the median numbers worldwide (9.95 and 1.4 pmp, respectively) (Table 2). [START_REF] Bello | Current status of end-stage kidney disease care in world countries and regions-an international survey[END_REF] There was, however, great variability within the region, with countries such as Greece, Italy, and Liechtenstein reporting more than 40 nephrologists pmp whereas the United Kingdom and Ireland both reported less than 10 nephrologists pmp. The most commonly reported workforce shortages were for both nephrologists (43%, n = 9) and dialysis nurses (43%, n = 9), followed by surgeons for HD access (38%, n = 8) and vascular access coordinators (29%, n = 6) (Supplementary Figure S1). Germany, Ireland, and Malta reported shortages of seven or more types of care providers, whereas Finland, France, Liechtenstein, Spain, and the United Kingdom did not report any workforce deficits.

Essential medications and health product access for kidney replacement therapy modalities

All countries in Western Europe had the capacity to provide chronic HD (Figure 3).

The median number of HD centers was 6.9 pmp (n = 21, IQR: 4.5-10.1), with the highest densities in Liechtenstein and Greece (25.94 and 15.80 pmp, respectively) and the lowest in the United Kingdom and Denmark (0.95 and 2.32 pmp, respectively) (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF] Home HD was available in 65% (n = 13) of countries in the region. In only one-third of countries (n = 7), more than 50% of HD patients began treatment with functioning vascular access (fistula or graft) (Supplementary Figure S2). In half of all countries (n = 10), 11-50% of patients started dialysis with a temporary dialysis catheter. PD was also widely available in all Western European countries (Figure 3). The median number of PD centers in the region was 2.3 pmp (n = 21, IQR: 1.8-3.6), which is above the global average. Liechtenstein and Switzerland had the highest PD capacity (centers pmp), whereas the United Kingdom and France had the lowest (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF][START_REF] Jain | Global trends in rates of peritoneal dialysis[END_REF] All countries in Western Europe were able to offer adequate frequency of PD exchanges (3-4 manual exchanges per day or equivalent cycles on automated PD), had the capacity to measure PD adequacy (via measurement of urea reduction ratio [URR] or Kt/V), and had efficient patient transport services available (Figure 3). Kidney transplantation was available across most of the region (n = 19, 90%), with a regional median of 0.52 transplant centers pmp (n = 19, IQR: 0.4-0.8), just above the global median of 0.42 pmp (IQR: 0.20-0.72) (Table 2). [START_REF]ERA-EDTA Registry Annual Report[END_REF] Iceland and Malta had the highest capacity for transplantation (5.82 and 2.23 transplant centers pmp, respectively), whereas Finland had the lowest (0.18 transplant centers pmp). All countries with transplant capacity performed a combination of deceased and living donor kidney transplants, with the exception of Iceland, which performs living donor kidney transplants only. The vast majority of countries with kidney transplantation available had national transplant waitlists (89%, n = 17), whereas the rest had regional lists only. Most countries were able to provide early and culturally appropriate information about transplantation to patients (95%, n = 19) (Figure 3). All countries in Western Europe were able to provide effective preventive therapy to control infections, timely access to operating space, appropriate immunosuppression treatment, and appropriate facilities to monitor immunosuppression drugs consistently. A standard organ procurement framework was available in all countries that have the capacity for transplantation.

In all surveyed countries in Western Europe, at least half of all patients with KF were able to access dialysis, a proportion that does not vary due to regional capacity or individual patient characteristics (Figure 4). Among those able to access dialysis, only a small minority (1-10%) began with PD in 50% of countries (n = 10); this proportion was affected by regional capacity and patient characteristics in 35% and 25% of countries, respectively. In four countries (Finland, Malta, Norway, and Sweden), 26-50% of patients began with PD. In 60% of countries (n = 12), more than 50% of eligible patients were able to access transplantation services.

Conservative care (non-dialytic management of KF) was available in the majority of countries (n = 18, 90%) in Western Europe when medically advised or chosen by the patient (Figure 3). Among those countries able to offer this service, 65% (n = 13) took a multidisciplinary approach to care via shared decision-making and had decision-making tools readily available for patients and providers. Most countries (85%, n = 17) had the capacity to systematically and actively recognize and manage symptoms. Twelve countries (60%) were able to provide psychological, cultural, and spiritual support, but only nine countries (45%) had the resources to systematically train healthcare providers in conservative care. However, regional data for countries were not available and conservative care accessibility may vary within countries.

Reporting of kidney replacement therapy quality indicators

Twenty countries were able to provide information about the adequacy of PD; 19 and 18 countries were able to provide the same information about HD and transplantation, respectively. The least-reported indicator of dialysis adequacy was patient-reported outcome measures, with almost one-third of countries reporting that this information was collected by fewer than 10% of centers (Supplementary Figure S3). Technique survival in HD patients was also less commonly measured by centers, as were delayed graft function and rejection rates in transplant recipients. Small solute clearance (e.g. Kt/V or creatinine clearance) was measured in >75% of centers in 95% of countries.

Health information systems, statistics, and national health policy

Most countries in Western Europe had official dialysis and transplantation registries (n = 18 and 19, respectively), few had CKD registries (n = 3, 14.3%), and only Malta and the United Kingdom had AKI registries (Figure 5). Iceland and Luxembourg had no registries at all, whereas only Malta and the United Kingdom had registries for every aspect of kidney care. Participation in registries was mandatory in 74% of countries (14/19) for kidney transplantation and 67% of countries for dialysis (12/18), but only 33% of countries (1/3) for CKD. Nearly all registries had national coverage and collect general information on the etiology of kidney disease, dialysis modality, or transplant source (Supplementary Figure S4). Patient outcome measures were not as consistently collected, with only 33% and 42% of hospitalizations recorded for dialysis and kidney transplant patients, respectively. Quality-oflife measures were very infrequently collected; however, mortality rates were recorded for almost all dialysis and transplant patients.

Routine testing for kidney disease is available to almost all patients with diabetes and hypertension in the region, but only in 50% of countries to chronic users of nephrotoxic medications and in 10% of countries to high-risk ethnic groups (despite 35% of countries identifying ethnic groups as being at high risk for CKD). Testing was available in 70% of countries for those with a family history of kidney disease (Figure 5). Only one and two countries had AKI and CKD detection programs, respectively. Services to treat and diagnose complications of KF were mostly available in the region (Supplementary Figure S5). Only 55% of countries (n = 11) in Western Europe had national strategies to improve care for CKD patients, including either CKD-specific strategies or those that had been incorporated into non-communicable disease strategies, the former being more inclusive of all patients with kidney disease than the latter (Supplementary Figures S6 andS7). National CKD-specific policies were available in only five countries (25%). Recognition of kidney disease as a health priority at the government level was more common for KF, followed by CKD and AKI (65%, 50%, and 5% of countries, respectively). Advocacy groups for KF, CKD, and AKI existed in 35%, 20%, and 25% of countries, respectively. The most commonly cited barriers to optimal KF care were geography (15%), the individual patient (15%), and lack of political will (15%), followed by nephrologists (10%) and economic factors (10%) (Figure 5).

Discussion

Our study highlights several important aspects of KF care in Western Europe. The median prevalence of treated KF was higher than the global median, and there was variation between countries even in Western Europe. HD remains the main dialysis modality, and PD remains under-utilized. There was also striking variation in the incidence of kidney transplantation between countries. In the majority of countries, public funding covered costs associated with non-dialysis CKD and KRT care. Although the median number of nephrologists and nephrology trainees in Western Europe was higher than the global average, workforce shortages of nephrologists and other essential healthcare staff were still reported across the region. Most countries had dialysis and transplant centers, and official registries to capture dialysis and transplant activities, but very few had AKI or CKD detection programs.

Only half of all countries in Western Europe had national strategies in place to improve CKD care.

All Western Europe is classified as a high-income region by the World Bank, however, there is substantial variation in treated KF incidence and prevalence rates. It has been proposed that varying prophylaxis programs, both in terms of primary prevention of CKD and how CKD progression is managed, as well as real differences in underlying CKD incidence may account for this variation, [START_REF] Heaf | Current trends in European renal epidemiology[END_REF] which persists even with stratification by diabetes, hypertension, and obesity. [START_REF] Bruck | CKD Prevalence Varies across the European General Population[END_REF] However, a decrease in KF incidence since 2001 has been noted among those between the ages of 60 and 69 in Denmark, from 400 ppm to 218 ppm, associated with a concurrent large increase in antihypertensive drug use, particularly drugs blocking the renin-angiotensin system (RAS). [START_REF] Heaf | Reduced incidence of end stage renal disease among the elderly in Denmark: an observational study[END_REF] There is substantial heterogeneity internationally in the control of hypertension with poorer than expected blood pressure control in some European cohorts. [START_REF] De Pinho | Considerable international variation exists in blood pressure control and antihypertensive prescription patterns in chronic kidney disease[END_REF] The EVEREST study, [START_REF] Caskey | Global variation in renal replacement therapy for end-stage renal disease[END_REF] an ERA-EDTA Registry initiative, identified GDP per capita and percentage of GDP spent on health care to be important in determining KRT incidence (i.e. there appears to be an 11% increase in KRT incidence associated with each 1% increase in GDP spent on health care), but some of the countries with the highest KF incidence such as Portugal, Greece, and Israel, have some of the lowest health expenditures. In Europe, the experience has been that dialysis has a disproportionately high impact on public health expenditure in countries with a lower GDP which carries the risk that this money is deviated from other urgent needs such as CKD primary and secondary prevention. [START_REF] Van Der Tol | A call for harmonization of European kidney care: dialysis reimbursement and distribution of kidney replacement therapies[END_REF] The risk of CKD progression can vary across countries even after accounting for the distributions of age, sex, comorbidities, and laboratory markers [START_REF] Orlandi | A collaborative, individual-level analysis compared longitudinal outcomes across the International Network of Chronic Kidney Disease (iNETCKD) cohorts[END_REF] and this variability has been demonstrated between Western European countries [START_REF] Bruck | Different rates of progression and mortality in patients with chronic kidney disease at outpatient nephrology clinics across Europe[END_REF] Other factors that have been proposed to explain the wide variation in incidence, include differences in genetic predisposition, [START_REF] Kottgen | Multiple loci associated with indices of renal function and chronic kidney disease[END_REF] birth weight, [START_REF] Silverwood | Low birth weight, later renal function, and the roles of adulthood blood pressure, diabetes, and obesity in a British birth cohort[END_REF] lifestyle factors such as exercise [START_REF] Stengel | Lifestyle factors, obesity and the risk of chronic kidney disease[END_REF] or dietary habits, [START_REF] Chrysohoou | Adherence to the Mediterranean diet is associated with renal function among healthy adults: the ATTICA study[END_REF] and public health strategies to control hypertension, [START_REF] Jafar | Progression of chronic kidney disease: the role of blood pressure control, proteinuria, and angiotensin-converting enzyme inhibition: a patient-level meta-analysis[END_REF] obesity 46 and tobacco consumption. [START_REF] Orth | Smoking as a risk factor for end-stage renal failure in men with primary renal disease[END_REF] Although PD was widely available in Western European countries, HD remained the most frequent dialysis modality used; only a small minority of patients began dialysis with PD. For certain candidates, PD has a number of advantages over HD, including preservation of residual kidney function, [START_REF] Marron | Benefits of preserving residual renal function in peritoneal dialysis[END_REF] greater independence, [START_REF] Bro | A prospective, randomized multicenter study comparing APD and CAPD treatment[END_REF] and better initial survival. [START_REF] Heaf | Initial survival advantage of peritoneal dialysis relative to haemodialysis[END_REF] The availability of home HD varied among countries, even though in highly selected patients, it is associated with lower costs, [START_REF] Krahn | Home Dialysis Is Associated with Lower Costs and Better Survival than Other Modalities: A Population-Based Study in Ontario, Canada[END_REF] less need for specialized personnel, better control of blood pressure, anemia, and phosphate levels, [START_REF] Wong | In-Center Nocturnal Hemodialysis Versus Conventional Hemodialysis: A Systematic Review of the Evidence[END_REF] improved quality of life, and greater flexibility for patients compared to in-center dialysis. [START_REF] Finkelstein | Effects of home hemodialysis on health-related quality of life measures[END_REF] There was striking variation in the incidence of kidney transplantation amongst Western European countries, ranging from 12 pmp in Luxembourg to 70.45 pmp in Spain.

With the exception of Iceland, Israel, and the Netherlands, the incidence of deceased donor kidney transplantation was much greater than that of living donor transplantation. Kidney transplantation is by far the most cost-effective KRT option due to a combination of prolonged survival, improved quality of life, and reduced medical costs after the first year. [START_REF] Wong | Comparative survival and economic benefits of deceased donor kidney transplantation and dialysis in people with varying ages and co-morbidities[END_REF] Funded by the EU, the Effect of Differing Kidney Disease Treatment Modalities and Organ Donation and Transplantation Practices on Health Expenditure and Patient Outcomes (EDITH) project was established in 2017 to examine the epidemiology and costs of different treatment modalities for KF, including the reasons behind the substantial variability in access to kidney transplantation. [START_REF] Jager | The effect of differing kidney disease treatment modalities and organ donation and transplantation practices on health expenditure and patient outcomes[END_REF] Some of the barriers appear to be fear of kidney rejection or graft failure, fear of surgery or medication, negative experiences with grafts (self or others), distrust of health care professionals, doing well on dialysis, religious opposition to transplantation, and costs, all of which underscore the need for improved patient education and communication. [START_REF] Vanholder | How to increase kidney transplant activity throughout Europe-an advocacy review by the European Kidney Health Alliance[END_REF] Better national health policies are clearly needed to improve the numbers. Different strategies may be required, depending on whether a country has a low level of deceased donor or living donor donation, or both. Countries with opt-out policies (or a practically defunct presumed consent system) such as Spain and Austria appear to have higher transplantation rates, [START_REF] Shepherd | An international comparison of deceased and living organ donation/transplant rates in opt-in and opt-out systems: a panel study[END_REF] suggesting that Western Europe may benefit from a global optout strategy. In an opt-out strategy, organ donation is the default option at the time of death, and so people must explicitly "opt-out" of organ donation if they do not wish it, as opposed to an opt-in policy which necessitates explicit consent. However, in a more recent analysis of organ donation and transplantation rates in 35 countries, no significant difference was observed in rates of kidney (35.2 versus 42.3 respectively), non-kidney (28.7 versus 20.9, respectively), or total solid organ transplantation (63.6 versus 61.7, respectively). [START_REF] Arshad | Comparison of organ donation and transplantation rates between opt-out and opt-in systems[END_REF] This suggests that there are other barriers to organ donation that need to be addressed including education and infrastructure, and that opt-out policies alone are unlikely to be successful. [START_REF] Matesanz | Opt-out legislations: the mysterious viability of the false[END_REF] Collaboration in broader programs such as Eurotransplant, Scandiatransplant and the South Transplant Alliance may also improve transplant activity. [START_REF] Zivcic-Cosic | Development of the Croatian model of organ donation and transplantation[END_REF] Another option may be to widen the donor pool to include expanded criteria donors and non-heartbeat donors, which are both under-utilized in Europe.

In 2019, upon request of the European Commission, the European Kidney Health Alliance (EKHA) formulated a joint statement of recommendations on how to improve organ donation and transplantation within the EU. [START_REF]European Kidney Health Alliance -Thematic Network on Improving Organ Donation and Transplantation in the EU. A Shared Vision for Improving Organ Donation and Transplantation in the EU[END_REF] Their key recommendations were to mobilize political will to make organ donation and transplantation a priority, to improve legal and institutional framework, to streamline organization and invest in leadership at all levels, to allocate appropriate funds for organ donation and transplantation programs, to promote 20 education and training across all stakeholders, to eradicate inequities in organ donation, to boost benchmarking, and to leverage research.

In the vast majority of countries, non-dialysis CKD and KRT care were publicly funded, but out-of-pocket co-payments varied. However, the annual costs of dialysis and kidney transplantation were more than twice as high in Western Europe as the global median.

Overall, 2% of health expenditures are allocated to KRT, which is required for just 0.1% of the population. [START_REF] Vanholder | Reducing the costs of chronic kidney disease while delivering quality health care: a call to action[END_REF] Promotion of more cost-effective forms of KRT (PD, home HD) or kidney transplantation may decrease financial pressure. Primary prevention of CKD by preventing underlying conditions such as diabetes mellitus and hypertension is also paramount.

Despite having more nephrologists and nephrology trainees in Western Europe compared to the rest of the world, there was much variation across the region, with countries such as Ireland and the United Kingdom both reporting less than 10 nephrologists pmp.

Crucially, Ireland and the United Kingdom did not have particularly low numbers of nephrology trainees, suggesting that a lack of judicious workforce planning was central to these disparities. Other proposed contributing factors include declining interest in nephrology among trainees, [START_REF] Parker | The future nephrology workforce: will there be one?[END_REF] over-reliance on foreign medical graduates, [START_REF] Lane | Nephrology: a specialty in need of resuscitation?[END_REF] and erosion of nephrology practice scope by other specialists. [START_REF] Berns | Training the next generation's nephrology workforce[END_REF] Patient-reported outcome measures were very infrequently collected in Western European kidney units and registries compared to other parts of the world. Their importance in healthcare is increasingly recognized, as they can quantify a wide variety of health concepts that are relevant to the patient, such as quality of life, functional status, and symptom burden. [START_REF] Tang | Patient-Reported Outcomes in Patients with Chronic Kidney Disease and Kidney Transplant-Part 1[END_REF] Patients with advanced CKD often experience poor health-related quality of life and numerous physical and emotional disease related symptoms. [START_REF] Fukuhara | Health-related quality of life among dialysis patients on three continents: the Dialysis Outcomes and Practice Patterns Study[END_REF] Routine collection of patient-reported outcome measures, as occurs in Australia and New Zealand, [START_REF] Morton | Use of patient-reported outcome measures and patient-reported experience measures in renal units in Australia and New Zealand: A cross-sectional survey study[END_REF] could improve symptom management, promote shared decision making, and better address patients' needs.

Very few countries had AKI or CKD registries, or corresponding detection programs. AKI registries not only enable better tracking of the epidemiology of AKI, its burden, associated mortality, and longer-term adverse kidney outcomes (i.e. subsequent development of CKD), but also facilitate temporal and regional comparisons. [START_REF] Sawhney | Epidemiology of AKI: Utilizing Large Databases to Determine the Burden of AKI[END_REF] Similarly, CKD registries permit longitudinal study and analysis of outcomes, and can generate prediction factors influencing the prognosis, care patterns, and disparities in the delivery of care. [START_REF] Larsson | Use of 13 disease registries in 5 countries demonstrates the potential to use outcome data to improve health care's value[END_REF] They create opportunities for quality improvement and KRT planning. However, the corollary is that registries are very time-consuming and costly when potentially affected individuals cannot be easily identified, and thus their contribution must be weighed against their cost. Populationbased screening for CKD is also controversial. Early detection of proteinuria in an unselected population has not been shown to be cost-effective. [START_REF] Boulware | Screening for proteinuria in US adults: a cost-effectiveness analysis[END_REF] However, the See Kidney Disease (SeeKD) targeted screening project in Canada that screened adults with risk factors for CKD (i.e., diabetes, hypertension, vascular disease, family history of kidney problems, etc.) identified a high proportion of individuals with risk factors for CKD and a high prevalence of unrecognized CKD. [START_REF] Galbraith | The See Kidney Disease Targeted Screening Program for CKD[END_REF] Kidney Disease: Improving Global Outcomes (KDIGO) recommends that all countries should have a targeted CKD screening program; [START_REF] Levey | Chronic kidney disease as a global public health problem: approaches and initiatives -a position statement from Kidney Disease Improving Global Outcomes[END_REF]

countries in Western

Europe generally comply with this recommendation by routinely testing all patients with hypertension, diabetes, and vascular disease. More uniform testing of high-risk ethnic groups or those with a family history of CKD is needed, however. Only about half of all countries recognize CKD as a health priority and have national strategies to improve care, with few specific policies. National CKD strategies can help develop a consistent approach to address key risk factors in the prevention, detection, and management of kidney diseases to minimize their progression and complications.

The most commonly cited barriers to kidney failure care were geography, the individual patient, and lack of political will (Figure 5). It has been shown rural patients have less access to dialysis units and home dialysis therapies when compared to urban patients, [START_REF] Rodriguez | Geographic information systems and chronic kidney disease: racial disparities, rural residence and forecasting[END_REF] and that that geographic location was associated with less frequent patient visits by dialysis providers. [START_REF] Erickson | Variation in nephrologist visits to patients on hemodialysis across dialysis facilities and geographic locations[END_REF] Patient-specific factors may include absence of symptoms, dialysis fears, workrelated concerns, socio-economic circumstances, and cultural differences. [START_REF] Griva | Patient-Related Barriers to Timely Dialysis Access Preparation: A Qualitative Study of the Perspectives of Patients, Family Members, and Health Care Providers[END_REF][START_REF] Lenz | Barriers to successful care for chronic kidney disease[END_REF] Lastly, it is well-recognized that improving global access to safe, sustainable, and equitable integrated kidney failure care will require key stakeholders at governmental and policymaker level. [START_REF] Harris | Increasing access to integrated ESKD care as part of universal health coverage[END_REF] In summary, the region is performing better in all aspects of kidney care overall compared to other regions, but improvements can be made through expansion of CKD prevention efforts, and realignment of priorities (less emphasis on KRT provision and more on prevention efforts). There is also a need for better workforce planning, multidisciplinary teams, and telemedicine. Collection and reporting of quality indicators, particularly patientreported outcomes, should be routinely incorporated into KF care. Health information systems should be expanded to prevent and manage KF. KF prevention and treatment should also be more broadly promoted by implementing policies, strategies, and advocacy programs, and mitigating barriers.

Role of the Funder/Sponsor

The ISN provided administrative support for the design and implementation of the study and data collection activities. The authors were responsible for data management, analysis, and interpretation, as well as manuscript preparation, review, and approval, and the decision to submit the manuscript for publication. outside the submitted work. ER reports personal fees and non-financial support from Alexion Pharmaceuticals, outside the submitted work. All other authors have nothing to declare.

Figure 1 :Figure 2 :

 12 Figure 1: Countries in the ISN Western Europe region that participated in the ISN-GKHA

Figure 3 :Figure 4 :Figure 5 .

 345 Figure 3: Availability of choice in kidney replacement therapy or conservative care for

Table 1 .

 1 Health finance, service delivery, and workforce prevalence in the 21 countries in Western Europe that participated in the ISN-GKHA survey.26,27,[START_REF]GDP ranking[END_REF][START_REF] Van Der Tol | An International Analysis of Dialysis Services Reimbursement[END_REF] Estimates are in US$ 2017 § Detailed reference list on annual cost of KRT is available in the Supplementary Appendix *Costs are in US$ 2016 ** Median and interquartile ranges are calculated for the selected countries in the ISN-GKHA survey only

	Country	Area (km 2 )	Total population (2018)	GDP (PPP) ($ billions) †	Total health expenditures (% of GDP) †	Annual cost KRT § (US$) & Out-of-pocket cost (% paid by patient from total cost)* HD KT PD (first year)
	Global** Median [IQR]	-	-	-	6.5 [4.9-8.8]	22,617 [14,882-49,690]	20,524 [14,305-33,905]	25,356 [6,138-17,522]
	Western Europe** Median [IQR]	-	-	441.0 [266.0-2,048.0]	9.8 [8.7-10.6]	60,037 [50,558-77,040]	47,963 [30,248-60,816]	54,342 [34,090-71,777]
	Austria	83,871	8,793,370	441.0	10.4	56,252 0%	30,248 0%	67,059 0%
	Belgium	30,528	11,570,762	529.2	10.0	67,512 0%	61,643 0%	38,451 0%
	Denmark	43,094	5,809,502	287.8	10.4	59,576 0%	28,102 0%	25,836 0%
	Finland	357,022	5,537,364	244.9	9.4	78,233 0%	66,816 0%	36,117 0%
	France	643,801	67,364,357	2856.0	11.1	85,436 1-25%	69,516 1-25%	114,220 1-25%
	Germany	357,022	80,457,737	4199.0	11.2	76,642	51,196	101,915
	Greece	131,957	10,761,523	299.3	8.4	45,435 0%	56,354 0%	63,196 0%
	Iceland	572	343,518	18.2	8.6	73,320 1-25%	17,155 1-25%	-1-25%
	Ireland	70,723	5,068,050	353.3	7.8	60,498 0%	36,926 0%	-0%
	Israel	20,770	8,424,904	317.1	7.4	56,174 0%	65,716 0%	-0%
	Italy	2,586	62,246,674	2317.0	9.0	46,912 0%	26,254 0%	71,461 0%
	Liechtenstein	160	38,547	5.0	-	-	-	-
	Luxembourg	2,586	605,764	62.1	6.0	-0%	-0%	-0%
	Malta	316	449,043	19.3	9.6	-0%	-0%	-0%
	Netherlands	41,543	17,151,228	924.4	10.7	103,187 1-25%	67,974 1-25%	71,882 1-25%
	Norway	323,802	5,372,191	381.2	10.0	50,847 0%	19,061 0%	33,414 0%
	Portugal	450,295	10,335,493	314.1	9.0	32,846 0%	32,109 0%	105,183 0%
	Spain	505,370	49,331,076	1778.0	9.2	56,602 0%	39,414 0%	45,487 0%
	Sweden	450,295	10,040,995	518.0	11.0	92,285 1-25%	83,193 1-25%	-1-25%
	Switzerland	41,277	8,292,809	523.1	12.1	67,800 1-25%	47,963 1-25%	-1-25%
	United Kingdom	243,610	65,105,246	2925.0	9.9	49,690 0%	31,505 0%	27,971 0%

Abbreviations: ISN: International Society of Nephrology; GKHA: Global Kidney Health Atlas; GDP: gross domestic product; PPP: purchasing power parity; KRT: kidney replacement therapy; HD: hemodialysis, PD: peritoneal dialysis; KT: Kidney transplant; IQR: interquartile range † "-": Data not reported/unavailable

Acknowledgement

We thank Kara Stephenson Gehman in ISN-GKHA for carefully editing the English text of a draft of this manuscript. We thank Jo-Ann Donner, Coordinator at the ISN, for her prominent role and leadership in the manuscript management, editorial reviews, and submission process to Kidney International Supplements, Sandrine Damster, Senior Research Project Manager at the ISN, and Alberta Kidney Disease Network staff (Ghenette Houston, Sue Szigety, and Sophanny Tiv) for helping to organize and conduct the survey and for providing project management support. We also thank the ISN headquarters staff including the Executive Director, Charu Malik, and the Advocacy team. We also appreciate the support from the ISN's Executive Committee, regional leadership, and Affiliated Society leaders at the regional and country levels for their help with the ISN-GKA survey.

Disclosure

KE reports grants from Astra Zeneca, Bayer, Fresenius, and Vifor, during the conduct of the study; personal fees from Akebia, Bayer, Fresenius and Vifor and grants from Amgen, Genzyme, and Shire, outside the submitted work. DWJ reports grants and personal fees from Baxter Healthcare and Fresenius Medical Care, travel sponsorship from Amgen, personal fees from Astra Zeneca, AWAK, and Ono, and grants from National Health and Medical Research Council of Australia, outside the submitted work. VJ reports grants from GlaxoSmithKline and Baxter Healthcare, provides scientific leadership to George Clinical, and consultancy fees for Biocon, Zudis Cadilla, and NephroPlus, all paid to his institution,

This work was supported by the International Society of Nephrology (Grant RES0033080 to the University of Alberta).

Table 2. Kidney replacement therapy and nephrology workforce statistics for the 21 countries in Western Europe that participated in ISN-GKHA survey. [START_REF]ERA-EDTA Registry Annual Report[END_REF][START_REF] Bello | Current status of end-stage kidney disease care in world countries and regions-an international survey[END_REF][START_REF] Jain | Global trends in rates of peritoneal dialysis[END_REF][START_REF]USRDS Annual Data Report: Epidemiology of kidney disease in the United States[END_REF]


Aline Thomas
email: aline.thomas.1@u-bordeaux.fr

Cécile Proust-Lima

Marion Baillet

Catherine Helmer

Cécile Delcourt

Alexandra Foubert-Samier

Gwénaëlle Catheline

Catherine Féart

Cécilia Samieri

Plasma carotenoids and medial temporal lobe atrophy in older adults

Keywords: Carotenoids, Biomarkers, Magnetic Resonance Imaging, Medial Temporal Lobe, Prospective studies, Risk factors in Epidemiology 3C, Three-City, APOEɛ4, ɛ4 allele of the apolipoprotein E gene, BMI, Body Mass Index, CI, confidence Interval, MRI, Magnetic Resonance Imaging, MTL, Medial Temporal Lobe, SD, Standard Deviation. YCLNU-D-20-00837R1

Background & aims: Carotenoids are vegetable pigments with neuroprotective properties.

Clinical studies found efficacy of specific carotenoids on improving brain perfusion and functioning with aging. However, evidence of an effect on neurodegeneration, which may require longer follow-up period to observe, is more limited. Leveraging biomarkers from a large population-based cohort study of older adults, we investigated whether blood carotenoids were associated with atrophy of the medial temporal lobe (a biomarker of neurodegeneration in aging) over 10 years.

Methods: This study included 461 dementia-free participants from the Three-City Bordeaux study (aged ≥65) who had plasma carotenoids measured at baseline and up to three repeated brain imaging exams in the subsequent 10 years.

Results:

In adjusted linear mixed models, each increase of 1 SD in plasma level of total carotenoids and of β-carotene was associated with 0.02 cm 3 (95% CI, 0.001-0.04; P = 0.04) and 0.02 cm 3 (95% CI, 0.01-0.04; P = 0.008) smaller medial temporal lobe volume loss per year, respectively.

Conclusions:

Our results based on a unique long-term prospective evaluation of a neuroimaging biomarker suggest a beneficial role of carotenoids for the prevention of agerelated neurodegeneration.

TEXT 1. Introduction

Carotenoids are vegetable pigments uniquely provided by diet with antioxidant, immunomodulatory and specific neuroprotective properties [START_REF] Craft | Carotenoid, tocopherol, and retinol concentrations in elderly human brain[END_REF][START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF]. Carotenes (found in orangeyellow fruits and vegetables) are precursors of retinoids, key signaling molecules for synaptic plasticity [START_REF] Craft | Carotenoid, tocopherol, and retinol concentrations in elderly human brain[END_REF]. The xanthophylls, lutein and zeaxanthin (found in green vegetables, orangeyellow fruits and corn) cross the blood-brain barrier, may decrease lipid peroxidation and stabilize lipid-protein structures in neuronal membranes [START_REF] Craft | Carotenoid, tocopherol, and retinol concentrations in elderly human brain[END_REF]. Serum carotenoid levels have been correlated to their concentration in the human brain [START_REF] Tanprasertsuk | Serum Carotenoids, Tocopherols, Total n-3 Polyunsaturated Fatty Acids, and n-6/n-3 Polyunsaturated Fatty Acid Ratio Reflect Brain Concentrations in a Cohort of Centenarians[END_REF].

Observational and clinical research has demonstrated associations of carotenoids with brain health [START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF][START_REF] Li | Dietary intakes of vitamin E, vitamin C, and β-carotene and risk of Alzheimer's disease: a meta-analysis[END_REF]. For example, clinical studies demonstrated efficacy of lutein and/or zeaxanthin supplementation on cognitive decline [START_REF] Nouchi | Effects of Lutein and Astaxanthin Intake on the Improvement of Cognitive Functions among Healthy Adults: A Systematic Review of Randomized Controlled Trials[END_REF] and on preservation of brain functional connectivity [START_REF] Lindbergh | The effects of lutein and zeaxanthin on resting state functional connectivity in older Caucasian adults: a randomized controlled trial[END_REF] and perfusion [START_REF] Lindbergh | Lutein and Zeaxanthin Influence Brain Function in Older Adults: A Randomized Controlled Trial[END_REF] with aging. However, evidence of an effect of carotenoids on brain structure and neurodegeneration, which may require longer follow-up period to observe, is more limited.

In a study, within the large population-based Three-City (3C) cohort, using biomarkers of carotenoid intake, we found associations between circulating carotenoid levels and a lower risk of dementia over the subsequent 10 years [START_REF] Feart | Plasma Carotenoids Are Inversely Associated With Dementia Risk in an Elderly French Cohort[END_REF]. Here, we further investigated whether blood carotenoids were also associated with atrophy of the medial temporal lobe (MTL), a biomarker of neurodegeneration in aging [START_REF] Jagust | Vulnerable neural systems and the borderland of brain aging and neurodegeneration[END_REF].

Materials and methods

The 3C study is a prospective cohort of non-institutionalized community dwellers (≥65 years), initiated in 1999-2000 in three French cities (Bordeaux, Dijon, Montpellier). All participants provided written consent and the study protocol was approved by the ethical committee of the YCLNU-D-20-00837R1 4 Kremlin-Bicêtre University-Hospital (Paris, France). In-person baseline data collection included sociodemographic and lifestyle information, medical history, blood pressure, anthropomorphic measurements, and neuropsychological testing. Plasma carotenoids (α and β-carotene, lycopene, lutein, zeaxanthin, β-cryptoxanthin) were measured in blood samples collected at baseline [START_REF] Feart | Plasma Carotenoids Are Inversely Associated With Dementia Risk in an Elderly French Cohort[END_REF]. In Bordeaux, an ancillary brain imaging study was conducted, with up to three repeated Magnetic Resonance Imaging (MRI) exams over 10 years (2000-2001, 2004-2006 and 2010-2011) allowing estimation of cerebral atrophy (using Freesurfer 5.1 software; see Supplementary Methods for details). MTL volume was defined as the sum of amygdalar, parahippocampal and hippocampal volumes of both hemispheres. The present study included 461 participants non-demented at baseline with plasma carotenoids measured at baseline and at least one analyzable anatomical scan (i.e. exclusion of major brain pathologies or major acquisition artefacts on MRI scans and post-processing failure; 61% had more than one MRI) (Supplementary Figure).

Plasma carotenoid levels were modeled as a continuous, standardized variables (i.e. for 1 SD increase), to account for the entire continuum of exposure. For descriptive analyses, we categorized carotenoid levels in four categories around mean ±1 SD.

The associations of blood carotenoids with MTL volume change over the three repeated MRI exams were estimated using linear mixed models; which included an intercept representing the MTL volume at baseline and a linear function of time representing the annual change in volume over time, with corresponding random intercept and slope to account for inter individual variability. To account for the change of protocol from a 1.5T to a 3T scanner at the last MRI examination, we added a last visit indicator (identifying a mean difference in volumes measured by the 3T scanner) and a scanner-specific variance for the measurement error (which captures a difference in the uncertainty of the volumes measured by the 3T and 1.5T scanners). Models were adjusted for age, sex, educational level, status for ɛ4 allele of the YCLNU-D-20-00837R1 apolipoprotein E gene (APOEɛ4; carrying at least one ɛ4 allele versus no ɛ4 allele), plasma triglycerides and total cholesterol concentrations, body mass index (BMI), smoking status (never, former, current), alcohol consumption, practice of regular physical activity, diabetes (fasting blood glucose ≥7.0 mmol/L, or treated), history of cerebral and cardiovascular diseases, hypertension (blood pressure ≥140/90 mmHg, or treated), hypercholesterolemia (plasma total cholesterol ≥6.2 mmol/L, or treated), high depressive symptoms (Center for Epidemiologic Studies-Depression scale score ≥17 for men and ≥23 for women, or being too depressed to answer), and total intracranial volume; and their interactions with time.

Missing data for covariates were imputed by multiple imputations (using chained equations with fully conditional specification method; M=5 imputations). Statistical analyses were performed using R version 3.6.0 (R Foundation). Two-sided p-values were used with an α=.05 threshold for statistical significance.

Results

The participants, aged 72.5 (±3.9) on average at baseline (Table ), were followed for a median time of 5.1 years (maximum 11.8). Individuals with higher blood carotenoid levels at baseline were more often female (P < 0.001) and APOEɛ4 carriers (P = 0.01), tended to practice more regular physical activity (P = 0.09), were less often smokers (P < 0.001), had higher fruits and vegetables intakes (P < 0.001), and a lower BMI (P < 0.001), were less often diabetics (P = 0.06), and hypertension (P = 0.005) but more hypercholesterolemia (P < 0.001) (Table ). In contrast, no difference was observed for educational level, cognitive performances, alcohol consumption, depressive symptoms, and history of cardiovascular diseases (all P > 0.05).

YCLNU-D-20-00837R1 YCLNU-D-20-00837R1

a P-values estimated using unadjusted linear regressions of the continuous measure of plasma total carotenoids with each covariate.

YCLNU-D-20-00837R1 8

In multivariable models, higher blood levels of total carotenoids and of β-carotene were associated with lower rates of subsequent MTL atrophy (Fig) . The mean differences in MTL volume change for each increase of 1 SD were 0.02 (95% CI, 0.001-0.04; P = 0.04) cm 3 /year and 0.02 (95% CI, 0.01-0.04; P = 0.008) cm 3 /year for total carotenoids and β-carotene, respectively. For comparison, the difference in MTL volume change for each 1 year increase in age at baseline was -0.007 (95% CI, -0.01 to -0.003) cm 3 /year; thus, the effect estimates for 1 SD of carotenoids was approximately equivalent to a 3-year-delay in brain atrophy (see

Supplementary Table for details).

Other carotenoids were not significantly associated with MTL atrophy. We found similar results when: (i) correcting carotenoid values by plasma lipids (cholesterol + triglycerides), which influence their bioavailability, (ii) modeling MTL relative to total intracranial volume, (iii) further adjusting for diet quality (using a Mediterranean diet score), (iv) running complete case analysis (n=417), and (v) after exclusion of incident cases of cardiovascular diseases during follow-up (n=428).

YCLNU-D-20-00837R1 at study baseline, with no higher than primary education level, APOEɛ4 non-carrier, who drinks ≥1 alcoholic beverages per week, does not smoke or practice regular physical activity, with a body mass index of 26 kg/m², triglycerides and total cholesterol concentrations of 1.2 mmol/L and 5.7 mmol/L respectively, without history of cerebral or cardiovascular diseases, diabetes or high depressive symptoms, with hypertension and hypercholesterolemia, and with a total intracranial volume of 900 cm 3 ). Note that the choice of profile is made to optimize graphical representation and has no influence on the differences in trajectories estimated by the model (calculated for each increase of 1 SD of plasma carotenoid level taken as a continuous variable). Linearity of the carotenoid association was assessed in sensitivity analyses.

YCLNU-D-20-00837R1

Discussion

In this large cohort, we found associations of plasma total carotenoids and β-carotene with MTL atrophy suggesting that dietary carotenoids may lower neurodegeneration with aging.

These results are in agreement with previous studies reporting associations between higher carotenoids intake and lower cognitive decline or risk of dementia; although most observational studies examined carotenoids through dietary questionnaires and epidemiological findings have been mixed overall [START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF][START_REF] Li | Dietary intakes of vitamin E, vitamin C, and β-carotene and risk of Alzheimer's disease: a meta-analysis[END_REF][START_REF] Feart | Plasma Carotenoids Are Inversely Associated With Dementia Risk in an Elderly French Cohort[END_REF].

We did not find any specific association of blood lutein and zeaxanthin with MTL atrophy, which contrasts with the reported associations of serum lutein with volume of the right parahippocampal cortex [START_REF] Zamroziewicz | Parahippocampal Cortex Mediates the Relationship between Lutein and Crystallized Intelligence in Healthy, Older Adults[END_REF] and with the clinical benefits of both xanthophylls on brain functional connectivity [START_REF] Lindbergh | The effects of lutein and zeaxanthin on resting state functional connectivity in older Caucasian adults: a randomized controlled trial[END_REF] and perfusion [START_REF] Lindbergh | Lutein and Zeaxanthin Influence Brain Function in Older Adults: A Randomized Controlled Trial[END_REF]. However, in an observational study like ours, blood status reflects both dietary intakes and internal metabolism, and comparison across observational and clinical studies is always difficult in nutrition science. The possibility that β-carotene, a precursor of retinoids involved in synaptic plasticity, is particularly potent to slower age-related neurodegeneration, as suggested by our findings, has biological plausibility and deserves further clinical evaluation. Indeed, preclinical studies showed that β-carotene and retinoids inhibits the deposition of amyloid beta in the brain and might slower neurodegeneration in Alzheimer's disease [START_REF] Craft | Carotenoid, tocopherol, and retinol concentrations in elderly human brain[END_REF][START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF]. Moreover, results from observational studies indicate that β-carotene levels are lower in patients with Alzheimer's disease as compared to healthy controls [START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF]. Prospective studies on β-carotene and cognitive aging yielded more conflicting results, but they were limited to studies using dietary questionnaires (prone to measurement error) to assess exposure, and cognitive change (and not specific biomarkers of neurodegeneration) as an outcome [START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF][START_REF] Li | Dietary intakes of vitamin E, vitamin C, and β-carotene and risk of Alzheimer's disease: a meta-analysis[END_REF].

YCLNU-D-20-00837R1

12

Our epidemiological results bring mechanistic insights into the potential beneficial role of carotenoids in brain aging. The MTL is primarily affected in Alzheimer's disease [START_REF] Jagust | Vulnerable neural systems and the borderland of brain aging and neurodegeneration[END_REF], and preclinical studies suggested that carotenoids may reduce the accumulation of brain amyloid (a core Alzheimer lesion) [START_REF] Cho | Recent Advances in Studies on the Therapeutic Potential of Dietary Carotenoids in Neurodegenerative Diseases[END_REF]. Besides, the MTL is one of the structures most vulnerable to aging, and its integrity appears critical for maintaining cognitive functions and mental health with aging [START_REF] Jagust | Vulnerable neural systems and the borderland of brain aging and neurodegeneration[END_REF]. Carotenoids may thus contribute to preserve vulnerable brain structures such as the MTL from aging and neurodegenerative processes, thereby delaying dementia.

Our study has several major strengths, including a large population-based sample with three repeated MRI exams over 10 years, and the evaluation of carotenoids exposure through blood biomarkers, limiting measurement errors in diet assessment. Moreover, our analyses were controlled for a large number of potential confounders, including lifestyle and diet quality.

A limitation of our study is the use of a single blood measurement, which might have caused misclassification in exposure assessment. However, baseline plasma carotenoids were significantly correlated with repeated assessments of fruit and vegetable intakes over the subsequent 10 years; and using a repeated blood measure in a subsample, we found acceptable stability of individual rankings between the two measurements a decade apart.

In summary, our findings based on blood biomarkers of dietary carotenoids and a unique long-term prospective evaluation of a MRI biomarker of neurodegeneration, suggest a beneficial role of carotenoids for the preservation of brain tissue integrity with aging that certainly deserves investigation in large clinical trials.

YCLNU-D-20-00837R1

Figure .

 . Figure. Mean trajectory of medial temporal lobe volume predicted by multivariable

Table . Baseline characteristics of participants, the 3C Bordeaux study, 1999-2011 (n=461)

 .

			Categories of plasma total carotenoids (µg/L)
	Characteristics	Total population	<574 (<mean -1 SD; N=59)	[574; 1168[ ([mean -1 SD; mean[;	[1168; 1762[ ([mean; mean +1	≥1762 (≥mean +1 SD; N=68)	P-values a
				N=214)	SD[; N=120)
	Age (year)	72.5 ± 3.9	72.4 ± 3.8	72.7 ± 4.1	72.4 ± 3.7	72.3 ± 3.9	0.66
	Female	269 (58.4)	20 (33.9)	117 (54.7)	78 (65.0)	54 (79.4)	<0.001
	Educational level (≤	243 (52.8)	39 (66.1)	106 (49.8)	63 (52.5)	35 (51.5)	0.85
	secondary)
	APOEɛ4	92 (20.2)	10 (16.9)	40 (19.0)	20 (16.9)	22 (32.4)	0.01
	MMSE score (range, 0-30)	27.9 ± 1.8	27.9 ± 1.6	27.8 ± 2.0	27.9 ± 1.6	27.9 ± 1.9	0.58
	Regular exercise	175 (41.2)	21 (37.5)	78 (40.0)	45 (40.5)	31 (49.2)	0.09
	Smoking						<0.001
	Never	276 (59.9)	26 (44.1)	118 (55.1)	80 (66.7)	52 (76.5)
	Ex-smoker	162 (35.1)	28 (47.5)	87 (40.7)	34 (28.3)	13 (19.1)
	Current smoker	23 (5.0)	5 (8.5)	9 (4.2)	6 (5.0)	3 (4.4)
	Alcohol consumption						0.54
	Never	63 (13.7)	8 (13.6)	27 (12.6)	16 (13.3)	12 (17.6)
	Former	11 (2.4)	1 (1.7)	5 (2.3)	2 (1.7)	3 (4.4)
	Current	387 (83.9)	50 (84.7)	182 (85.0)	102 (85.0)	53 (77.9)
	Fruits and vegetables intake	15.8 ± 3.3	14.3 ± 3.8	15.7 ± 3.5	16.5 ± 2.8	16.6 ± 2.6	<0.001
	(serving/week)
	Body Mass Index (kg/m²)	26.0 ± 3.7	27.4 ± 4.3	26.3 ± 3.3	25.8 ± 3.7	24.5 ± 3.4	<0.001
	Diabetes	36 (7.9)	7 (11.9)	20 (9.4)	6 (5.0)	3 (4.5)	0.06
	History of cardiovascular	117 (25.4)	13 (22.0)	59 (27.6)	32 (26.7)	13 (19.1)	0.43
	diseases
	High depressive symptoms	22 (4.8)	3 (5.1)	12 (5.6)	5 (4.2)	2 (2.9)	0.44
	Hypertension	338 (73.3)	45 (76.3)	165 (77.1)	84 (70.0)	44 (64.7)	0.005
	Hypercholesterolemia	260 (56.4)	24 (40.7)	113 (52.8)	81 (67.5)	42 (61.8)	<0.001
	Plasma lipids (mmol/L)
	Total cholesterol	5.7 ± 0.9	5.4 ± 0.8	5.6 ± 0.9	6.0 ± 1.0	6.2 ± 1.0	<0.001
	Triglycerides	1.2 ± 0.5	1.2 ± 0.6	1.2 ± 0.5	1.2 ± 0.5	1.1 ± 0.5	0.08
	MTL volume (cm 3 )	15.7 ± 1.7	15.7 ± 1.8	15.8 ± 1.8	15.8 ± 1.5	15.4 ± 1.6	0.11
	Plasma carotenoids (µg/L)
	Total carotenoids	1168 ± 594	432 ± 98	885 ± 165	1410 ± 156	2274 ± 454
	β-carotene	435 ± 331	109 ± 49	288 ± 103	521 ± 150	1028 ± 378
	α-carotene	103 ± 93	39 ± 16	72 ± 37	118 ± 64	231 ± 152
	Lycopene	253 ± 175	110 ± 59	197 ± 109	309 ± 156	451 ± 232
	Lutein	166 ± 83	95 ± 41	150 ± 64	205 ± 95	210 ± 86
	Zeaxanthin	40 ± 22	23 ± 12	37 ± 18	48 ± 26	50 ± 22
	β-cryptoxanthin	171 ± 124	57 ± 37	140 ± 79	209 ± 123	303 ± 150
	3C, Three-City; APOEɛ4, ɛ4 allele of the apolipoprotein E gene; MMSE, Mini-Mental State
	Examination; MTL, medial temporal lobe.
	Data are given as mean ± SD and n (%) and are for non-missing values. Missing baseline

values: 0.2% for educational level and MMSE score, 0.9% for diabetes, 1.1% for APOEɛ4 status, 7.8% for regular exercise, 10.4% for MTL volume.

Acknowledgments/Funding sources

The Three-City Study is conducted under a partnership agreement between the Institut National de la Santé et de la Recherche Médicale (INSERM), the Institut de Santé Publique et Développement of the University of Bordeaux and Sanofi-Aventis. The Fondation pour la Recherche Médicale funded the preparation and initiation of the study. The Three-City Study is also supported by the Caisse Nationale Maladie des Travailleurs Salariés, Direction Générale de la Santé, Mutuelle Générale de l'Education Nationale, Institut de la Longévité, Regional Governments of Aquitaine and Bourgogne, Fondation de France, Ministry of Research-INSERM Programme "Cohortes et collections de données biologiques", French National Research Agency COGINUT ANR-06-PNRA-005 and ANR 2007LVIE 003, the Fondation Plan Alzheimer (FCS 2009-2012), the Caisse Nationale pour la Solidarité et l'Autonomie (CNSA), and Roche Pharma. The sponsors were not involved in the design and conduct of the study or in the data analyses or manuscript elaboration. Aline Thomas was part of the University Research school (École Universitaire de Recherche, EUR) Digital Public Health PhD program, supported within the framework of the French National Research Agency (ANR) "Programme d'Investissement d'Avenir" (Investment for the Future) PIA3 (17-EURE-0019). and design of the study, the drafting of the manuscript and supervised the research project. C.P-L. contributed to statistical analyses and provided significant advice. M.B., A.F-S., G.C., and C.F. were implicated in the acquisition of the data and provided significant advice. C.H. and C.D. obtained funding, were implicated in the acquisition of the data and provided significant advice. All authors critically reviewed the manuscript. YCLNU-D-20-00837R1

Conflicts of interest