Is there any survival advantage of obesity in Southern European haemodialysis patients?

Background. In the general population, a high body mass index (BMI) is associated with increased cardiovascular disease and all-cause mortality. However, according to US epidemiological evaluation in maintenance haemodialysis (HD) patients, a reverse epidemiology is described and baseline obesity appears paradoxically associated with better survival. The aim of this study is to examine in a Southern European HD population the relationship between survival and BMI at the start of HD treatment, and how survival is influenced by the body weight (BW) variations during the first year of treatment. Methods. A total of 85 dialysis centres located in Portugal, France and Italy and belonging to the FME European dialysis chain were included. The current prospective analysis focuses on incident patients admitted to these centres between 1 January 2000 and 30 September 2005 with <1 month of previous follow-up on RRT. Data were gained from the FME EuCliD database. Patients were classified at baseline in four categories according to the BMI: underweight, normal range, overweight and obese. Also, the patient survival was analysed according to five quintiles of BW changes during the first year of HD treatment <-5.8%, -5.8 to -1.1%, -1.1 to 1.7% ( reference category), +1.7 to +5.5% and >+5.5%. Survival analysis was adjusted for a set of demographic and comorbids using Kaplan-Meier curves and Cox model. Hazard ratios and their 95% confidence intervals were calculated with the use of the estimated regression coefficients and their standard errors. Results. A total of 5592 patients were analysed (40.9% females), and the mean age at admission was 64.4 +/- 16.5 years. Of them, 27.7% were diabetic. The mean follow-up was 2.0 +/- 1.6 years. Almost half of the patients (46.4%) were in the normal range of BMI (20-24.9 kg/m(2)). When analysed with the Cox model, the categories of baseline BMI ( underweight, normal range, overweight and obese) significantly influenced the survival with the respective hazard ratio (HR) and confidence interval at 1.14 (0.96-1.35), 1, 0.74 (0.67-0.9) and 0.78 (0.56-0.87). The strength of the association as well as the shape of the curve remains unchanged after considering age, diabetes and comorbidities. Moreover, when compared to patients for whom BW remained stable during the first year of HD treatment, survival was significantly lower in patients presenting in the lower quintile of BW variation (<-5.8% in 1 year) with an HR of 1.6. Conclusions. Despite increased comorbidities, overweight and obese patients on maintenance HD carry a significant lower mortality risk than patients in the normal and lower BMI ranges. This confirms the reverse epidemiology previously reported in US HD patients for these categories of BMI. Also BW variation during the first year of HD treatment is associated with patient survival, highlighting the importance of nutrition in this setting.