Exercise Capacity and All-Cause Mortality in African American and Caucasian Men With Type 2 Diabetes

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Abstract
OBJECTIVE: The purpose of this study was to assess the association between exercise capacity and mortality in African Americans and Caucasians with type 2 diabetes and to explore racial differences regarding this relationship. RESEARCH DESIGN AND METHODS: African American (n = 1,703; aged 60 ± 10 years) and Caucasian (n = 1,445; aged 62 ± 10 years) men with type 2 diabetes completed a maximal exercise test between 1986 and 2007 at the Veterans Affairs Medical Centers in Washington, DC, and Palo Alto, California. Three fitness categories were established (low-, moderate-, and high-fit) based on peak METs achieved. Subjects were followed for all-cause mortality for 7.3 ± 4.7 years. RESULTS: The adjusted mortality risk was 23% higher in African Americans than in Caucasians (hazard ratio 1.23 [95% CI 1.1–1.4]). A graded reduction in mortality risk was noted with increased exercise capacity for both races. There was a significant interaction between race and METs (P < 0.001) and among race and fitness categories (P < 0.001). The association was stronger for Caucasians. Each 1-MET increase in exercise capacity yielded a 19% lower risk for Caucasians and 14% for African Americans (P < 0.001). Similarly, the risk was 43% lower (0.57 [0.44–0.73]) for moderate-fit and 67% lower (0.33 [0.22–0.48]) for high-fit Caucasians. The comparable reductions in African Americans were 34% (0.66 [0.55–0.80]) and 46% (0.54 [0.39–0.73]), respectively. CONCLUSIONS: Exercise capacity is a strong predictor of all-cause mortality in African American and Caucasian men with type 2 diabetes. The exercise capacity-related reduction in mortality appears to be stronger and more graded for Caucasians than for African Americans.