BMI-mortality paradox and fitness in African American and Caucasian men with type 2 diabetes

Abstract

Objective: To assess the association between BMI, fitness, and mortality in African American and Caucasian men with type 2 diabetes and to explore racial differences in this association.

Research design and methods: We used prospective observational data from Veterans Affairs Medical Centers in Washington, DC, and Palo Alto, California. Our cohort (N = 4,156; mean age 60 ± 10.3 years) consisted of 2,013 African Americans (mean age, 59.5 ± 9.9 years), 2,000 Caucasians (mean age, 60.8 ± 10.5 years), and 143 of unknown race/ethnicity. BMI, cardiac risk factors, medications, and peak exercise capacity in metabolic equivalents (METs) were assessed during 1986 and 2010. All-cause mortality was assessed across BMI and fitness categories.

Results: There were 1,074 deaths during a median follow-up period of 7.5 years. A paradoxic BMI-mortality association was observed, with significantly higher risk among those with a BMI between 18.5 and 24.9 kg/m(2) (hazard ratio [HR] 1.70 [95% CI 1.36-2.1]) compared with the obese category (BMI ≥ 35 kg/m(2)). This association was accentuated in African Americans (HR 1.95 [95% CI 1.44-2.63]) versus Caucasians (HR 1.53 [1.0-2.1]). The fitness-mortality risk association for the entire cohort and within BMI categories was inverse, independent, and graded. Mortality risks were 12% lower for each 1-MET increase in exercise capacity, and ~35-55% lower for those with an exercise capacity >5 METs compared with the least fit (≤ 5 METs). CONCLUSIONS A paradoxic BMI-mortality risk association was observed in African American and Caucasian patients with diabetes. The exercise capacity-mortality risk association was inverse, independent, and graded in all BMI categories but was more potent in those with a BMI ≥ 25 kg/m(2).

Figure 1

Adjusted mortality risk (95% CI) according to BMI categories. *Different from the highest BMI category (≥35 kg/m²).

Figure 2

Adjusted mortality risk within each fitness category for diabetic individuals with and without additional risk factors. *Different from lowest fit category (≤5 METs) with no additional risk factors.