Background: Haemodialysis (HD) patients with lower body mass index (BMI) have a higher relative mortality risk (RR), irrespective of race. However, only Asian Americans treated with HD have been found to have an elevated RR with higher BMI. Asian Americans on HD are 'healthier' than other race groups (i.e. have better overall survival). We hypothesized that an increased mortality risk might be associated with high BMI in a variety of other 'healthier' subgroups of HD patients.
Methods: The prospective Dialysis Outcomes and Practice Patterns Study (DOPPS) provided baseline demographic, comorbidity and BMI data on 9714 HD patients in the US and Europe (France, Germany, Italy, Spain, and the UK) from 1996-2000. Using multivariate survival analyses, we evaluated BMI-mortality relationships in HD subpopulations defined by continent, race (black and white), gender, tertiles of severity of illness (based on a score derived from comorbid conditions and serum albumin concentration), age (<45, 45-64, >or=65), smoking, and diabetic status.
Results: Relative mortality risk decreased with increasing BMI. This was statistically significant (P<0.007) except for the smallest subgroup of patients who were <45 years old and were also in the healthiest tertile of comorbidity. All else equal, BMI <20 was consistently associated with the highest relative mortality risk. Overall a lower relative mortality risk (RR) as compared with BMI 23-24.9, was found for overweight (BMI 25-29.9; RR 0.84, P=0.008), for mild obesity (BMI 30-34.9; RR 0.73, P=0.0003), and for moderate obesity (BMI 35-39.9; RR 0.76, P=0.02).
Conclusion: In a wide variety of HD patient subgroups, differing with respect to their baseline health status, increasing body size correlates with a decreased mortality risk. This contrasts with the association between BMI and mortality in the general population, and deserves further study.