Cardiorespiratory Fitness, Glycemic Status, and Mortality Risk in Men

Abstract

Objective — To determine the association of baseline cardiorespiratory fitness to all-cause mortality across the range of blood glucose levels. Research Design And Methods — Data from a prospective study of 8715 men (average age 42 yr), followed for an average of 8.2 yr (range 1-15 yr), were analyzed. Cardiorespiratory fitness was assessed by maximal-exercise treadmill testing. Men with evidence of clinical vascular disease or who did not achieve 85% of their age-predicted maximum heart rate during exercise testing were excluded from analyses. Results — Age-adjusted death rates increased with higher levels, of fasting blood glucose. Regardless of glycemic status, fit men had lower age-adjusted all-cause death rates than their less fit counterparts. For men with fasting blood glucose ≥ 7.8 mM or physician-diagnosed non-insulin-dependent diabetes mellitus (NIDDM), the age-adjusted death rates per 10,000 person-yr of follow-up in unfit and fit subjects were 82.5 and 45.9, respectively. The age-adjusted relative risk of death due to all causes was significantly elevated in the lower-fitness group within each of three glycemic status levels: fasting blood glucose <6.4 mM; relative risk (RR) = 1.93 (95% confidence interval [95% CI] 1.15-3.26); fasting blood glucose 6.4-7.8 mM; RR = 3.42 (95% CI 2.27-5.15); and fasting blood glucose ≥ 7.8 mM or with NIDDM, RR = 1.80 (95% CI = 1.25-2.58). Multivariate analyses, controlling for risk factors of mortality (age, resting systolic blood pressure, serum cholesterol, body mass index, family history of heart disease, follow-up interval, and smoking habit) showed a higher risk of death due to all causes for unfit compared with fit men. Multivariate risks of death associated with low fitness, compared with higher fitness (RR), in the three glycemic status groups were: fasting blood glucose <6.4 mM, RR = 1.38 (95% CI 1.09-1.74); fasting blood glucose 6.4-7.8 mM, RR = 1.61 (95% CI 0.91-2.86); and fasting blood glucose ≥7.8 mM or with NIDDM, RR = 1.92 (95% CI 0.75-4.90). Conclusions — These data suggest that risk of death increases with lessfavorable glycemic status, and that cardiorespiratory fitness may attenuate the forces of impaired carbohydrate metabolism on mortality from any cause.