Purpose End-stage renal disease (ESRD) has doubled in the past decade in the United States. Furthermore, blacks have a higher risk of ESRD compared with whites, although the reason for this is not entirely known. Obesity is associated with increased risk of ESRD and death in the general population and blacks have a higher prevalence of obesity compared with other racial groups. Therefore, the aim of this study is to test the hypothesis that there is a racial difference in the association of obesity with ESRD risk and death.
Methods Data were analyzed from the Cooperative Cardiovascular Project (CCP), which observed 234,754 Medicare patients seen for acute myocardial infarction (AMI) between February 1994 and July 1995. Patients were followed until ESRD or death, as determined by the U.S. Renal Data registry and Medicare database. BMI was calculated as weight (kg) divided by height (meters squared) and categorized according to National Heart and Lung Blood Institute (NHLBI) guidelines as either underweight, normal, overweight, class 1, class 2, or class 3 obesity. Outcomes included ESRD and death. All analyses, including Cox proportional hazard models, were conducted using SAS software version 9.1.
Results Mean BMI was higher among blacks than whites (27.0 vs 26.0, p < .0001), and there was no significant interaction between race and BMI class on ESRD rate (p = .5). Moreover, BMI class was not significantly associated with ESRD rate and compared with normal BMI, multivariate hazard ratios (HR) on all BMI classes were less than 1 but nonsignificant. In regard to overall survival, there was a significant association between race and BMI class (p < .05). The overweight, class 1, and class 2 obese had better survival compared with normal-weight patients (overweight black HR: 0.83, 95% CI 0.77-0.90; overweight white HR: 0.84, 95% CI 0.80-0.86; obese 1 black HR: 0.78, 95% CI 0.71-0.87; obese 1 white HR: 0.84, 95% CI 0.81-0.86; obese 2 black HR: 0.83, 95% CI 0.71-0.97; obese 2 white HR: 0.84, 95% CI 0.80-0.89). Class 3 obesity was associated with better survival among whites (HR: 0.89, 95% CI 0.83-0.97) but not blacks (HR: 1.13, 95% CI 0.92-1.39). Survival in the underweight class was worse among both blacks and whites.
Conclusion In contrast to studies concluding the association of obesity and ESRD, this association may not apply for elderly patients with prevalent coronary heart disease. In addition, there may be some mortality benefit in obese elderly patients, especially blacks with high-risk cardiovascular disease.
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