The Joint Effects of Physical Activity and Body Mass Index on Coronary Heart Disease Risk in Women

Background: Physical activity and body mass index (calculated as weight in kilograms divided by height in meters squared) independently alter the risk of coronary heart disease (CHD); however, their combined effect on CHD is not established. Our objective was to study the combined association of physical activity and body mass index on CHD.

Methods: Prospective cohort study of 38,987 women free of cardiovascular disease, cancer, and diabetes at baseline in the Women's Health Study, with 10.9 mean years of follow-up. Weight, height, and recreational activities were reported on entry. Body mass index was categorized as normal weight (<25), overweight (25 to <30), and obese (> or =30). Active was defined as 1000 kilocalories or more expended on recreational activities weekly. Six joint body weight-physical activity categories were defined. The main outcome measure was the occurrence of incident CHD during follow-up, defined as a cardiovascular event including nonfatal myocardial infarction, coronary artery bypass graft, percutaneous transluminal coronary angioplasty, or CHD death.

Results: A total of 948 cases of incident CHD occurred during follow-up. Higher body mass index and physical inactivity were individual predictors of CHD. In joint analyses, compared with active normal-weight individuals, the multivariate-adjusted hazard ratios (95% confidence intervals) were 1.54 (1.14-2.08) for overweight-active; 1.87 (1.29-2.71) for obese-active; 1.08 (0.84-1.39) for normal weight-inactive; 1.88 (1.46-2.42) for overweight-inactive; and 2.53 (1.94-3.30) for obese-inactive. Increasing levels of walking also resulted in significant reductions in CHD risk for overweight and obese individuals.

Conclusions: The risk of CHD associated with elevated body mass index is considerably reduced by increased physical activity levels. However, the risk is not completely eliminated, reinforcing the importance of being lean and physically active.