Intensity and Amount of Physical Activity in Relation to Insulin Sensitivity: The Insulin Resistance Atherosclerosis Study

Abstract

CONTEXT: Exercise training is associated with improved insulin sensitivity (SI), but the potential impact of habitual, nonvigorous activity is uncertain. OBJECTIVE: To determine whether habitual, nonvigorous physical activity, as well as vigorous and overall activity, is associated with better SI. DESIGN: A multicultural epidemiologic study. SETTING: The Insulin Resistance Atherosclerosis Study, conducted in Oakland, Calif; Los Angeles, Calif; the San Luis Valley, Colo; and San Antonio, Tex. PARTICIPANTS: A total of 1467 men and women of African American, Hispanic, and non-Hispanic white ethnicity, aged 40 to 69 years, with glucose tolerance ranging from normal to mild non-insulin-dependent diabetes mellitus. MAIN OUTCOME MEASURE: Insulin sensitivity as measured by an intravenous glucose tolerance test. RESULTS: The mean SI for individuals who participated in vigorous activity 5 or more times per week was 1.59 min(-1) x microU(-1) x mL(-1) x 10(-4) (95% confidence interval [CI], 1.39-1.79) compared with 0.90 (95% CI, 0.83-0.97) for those who rarely or never participated in vigorous activity, after adjusting for potential confounders (P<.001). When habitual physical activity (estimated energy expenditure [EEE]) was assessed by 1-year recall of activities, the correlation coefficient between SI and total EEE was 0.14 (P<.001). After adjustment for confounders, vigorous and nonvigorous levels of EEE (metabolic equivalent levels > or = 6.0 and <6.0, respectively) were each positively and independently associated with SI (P< or =.01 for each). The association was attenuated after adjustment for the potential mediators, body mass index (a measure of weight in kilograms divided by the square of the height in meters), and waist-to-hip ratio. Results were similar for subgroups of sex, ethnicity, and diabetes. CONCLUSIONS: Increased participation in nonvigorous as well as overall and vigorous physical activity was associated with significantly higher SI. These findings lend further support to current public health recommendations for increased moderate-intensity physical activity on most days.