Racial and ethnic differences in the association of body mass index and survival in maintenance hemodialysis patients

Abstract

Background: In maintenance hemodialysis (HD) patients, overweight and obesity are associated with survival advantages. Given the greater survival of maintenance HD patients who are minorities, we hypothesized that increased body mass index (BMI) is associated more strongly with lower mortality in blacks and Hispanics relative to non-Hispanic whites.

Study design: Retrospective cohort study.

Setting & participants: We examined a 6-year (2001-2007) cohort of 109,605 maintenance HD patients including 39,090 blacks, 17,417 Hispanics, and 53,098 non-Hispanic white maintenance HD outpatients from DaVita dialysis clinics. Cox proportional hazards models examined the association between BMI and survival.

Predictors: Race and BMI.

Outcomes: All-cause mortality.

Results: Patients had a mean age of 62 ± 15 (standard deviation) years and included 45% women and 45% patients with diabetes. Across 10 a priori-selected BMI categories (<18-≥40 kg/m(2)), higher BMI was associated with greater survival in all 3 racial/ethnic groups. However, Hispanic and black patients experienced higher survival gains compared with non-Hispanic whites across higher BMI categories. Hispanics and blacks in the ≥40-kg/m(2) category had the largest adjusted decrease in death HR with increasing BMI (0.57 [95% CI, 0.49-0.68] and 0.63 [95% CI, 0.58-0.70], respectively) compared with non-Hispanic whites in the 23- to 25-kg/m(2) group (reference category). In linear models, although the inverse BMI-mortality association was observed for all subgroups, overall black maintenance HD patients showed the largest consistent decrease in death HR with increasing BMI.

Limitations: Race and ethnicity categories were based on self-identified data.

Conclusions: Whereas the survival advantage of high BMI is consistent across all racial/ethnic groups, black maintenance HD patients had the strongest and most consistent association of higher BMI with improved survival.

Figure 1

Unadjusted or crude mortality rate in different races across body mass index (BMI) categories

Figure 2

Hazard ratios (95% confidence intervals) of mortality across the body mass index (BMI) categories, obtained from Cox regression analyses of combined data on all three racial/ethnic groups in unadjusted (A), case-mix (B) and case-mix and MICS adjusted model (C). The case-mix model we adjusted for: age, gender, 10 pre-existing co-morbid states, categories of dialysis vintage, primary insurance, marital status, and residual urinary urea clearance during the entry quarter. MICS-adjusted models include all the case-mix covariates plus nPNA, serum levels of albumin, total iron-binding capacity, ferritin, creatinine, phosphorus, calcium, bicarbonate, blood white blood cell count, lymphocyte percentage and hemoglobin.

Figure 3

Coefficient estimates and standard errors obtained from Cox regression model using body mass index (BMI) as a continuous variable among different races. Estimates have been adjusted for age, gender, and 10 pre-existing co-morbid states, categories of dialysis vintage, primary insurance, marital status, and residual urinary urea clearance during the entry quarter; nPNA, serum levels of albumin, total iron-binding capacity, ferritin, creatinine, phosphorus, calcium, bicarbonate, blood white blood cell count, lymphocyte percentage and hemoglobin.