Association of body size with outcomes among patients beginning dialysis

Background: Although obesity confers an increased risk of mortality in the general population, observational reports on the dialysis population have suggested that obesity is associated with improved survival. These reports have generally not examined extremely high values of body mass index (BMI; in kg/m(2)), survival >1 y, or alternative measures of adiposity. Objective: We sought to clarify the relation between body size and outcomes among a large cohort of patients beginning dialysis. Design: Data on 418 055 patients beginning dialysis between I April 1995 and 1 November 2000 were analyzed by using US Renal Data System data. BMI was divided into 8 categories in increments of 3 units, ranging from <19 to greater than or equal to37, and the relation between survival and BMI was examined by using proportional hazards regression with adjustment for demographic, laboratory, and comorbidity data. Results: High BMI was associated with increased survival in this cohort, even at extremely high BMI, after adjustment, and over a 2-y average follow-up time. This was true for whites, African Americans, and Hispanics but not for Asians. High BMI was also associated with a reduced risk of hospitalization and a lower rate of mortality in all mortality categories. Alternative estimates of adiposity, including the Berm index and estimated fat mass, yielded similar results, and adjustments for lean body mass did not substantially alter the findings. Conclusions: High BMI is not associated with increased mortality among patients beginning dialysis. This finding does not appear to be a function of lean body mass and, although modified by certain patient characteristics, it is a robust finding.