Increasing body mass index (BMI) is associated with lower mortality rates in maintenance hemodialysis (HD) patients regardless of race or ethnicity, but the survival advantage is most pronounced in blacks, data show.

A study of 109,605 maintenance HD patients showed that each 1 kg/m2 increment in BMI was associated with a 2.5% lower mortality risk in blacks, a 2.0% lower risk in non-Hispanic whites, and a 1.0% lower risk in Hispanics.

A possible reason for the stronger survival advantage associated with higher BMI in blacks compared with other races or ethnicities is that blacks have greater muscle mass, and more muscle mass appears to be associated with better survival, according to the researchers.

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The investigators, led by Kamyar Kalantar-Zadeh, MD, PhD, MPH,  of the Harbor-UCLA Medical Center in Torrance, Calif., published their findings in the American Journal of Kidney Diseases (2011; 58:4:574-582). As far as they are aware, their study is the first to compare the association between BMI and survival in blacks, non-Hispanic whites, and Hispanics in maintenance HD patients.

Previous studies have shown that black and Hispanic maintenance dialysis patients have a lower mortality rate than their non-Hispanic white counterparts, an advantage that persists even after adjusting for such important factors as comorbid diseases and laboratory result abnormalities, Dr. Kalantar-Zadeh’s group noted.

Obesity is associated with an increased risk of death in the general population, but in the dialysis population, obese individuals consistently have been shown to have a relatively lower death risk compared with non-obese individuals. The reasons for what researchers call the “obesity paradox” in the dialysis population remain unclear, but one possible explanation is that obese individuals have greater nutritional reserves that prevent protein-energy wasting, a common and potentially life-threatening condition faced by dialysis patients.