Physical activity, metabolic factors, and the incidence of coronary heart disease and type 2 diabetes

Objective: To examine the role of nonfasting serum insulin level and compon ents of the insulin resistance syndrome in the relationship between physica l activity and the incidence of coronary heart disease and type 2 diabetes. Methods: Prospective study of 5159 men aged 40 to 59 years with no history of coronary heart disease, type 2 diabetes, or stroke drawn from general pr actices in 18 British towns. During an average follow-up period of 16.8 yea rs, there were 616 cases of major coronary heart disease events (fatal and nonfatal) and 196 incident cases of type 2 diabetes. Results: After adjustment for potential confounders (lifestyle characterist ics and preexisting disease), physical activity was inversely related to co ronary heart disease rates, with the lowest rates in the men undertaking mo derate physical activity and with no further benefit thereafter. For type 2 diabetes, risk decreased progressively with increasing levels of physical activity. Physical activity was associated with serum insulin level and wit h factors associated with insulin, ie, heart rate, hyperuricemia, diastolic blood pressure, and high-density lipoprotein cholesterol level, and with g amma-glutamyltransferase level, a possible marker of hepatic insulin resist ance. Adjustment for insulin and associated factors made little difference to the relationship between physical activity and risk of coronary heart di sease. By contrast, these factors together with gamma-glutamyltransferase l evel appear to explain a large proportion of the reduction in risk of type 2 diabetes associated with physical activity. Conclusions: The relationship between physical activity and type 2 diabetes appears to be mediated by serum true insulin level and components of the i nsulin resistance syndrome. However, these factors do not appear to explain the inverse relationship between physical activity and coronary heart dise ase.