Seasonal variations in coronary heart disease

Coronary heart disease exhibits a winter peak and summer trough in incidence and mortality, in countries both north and south of the equator. In England and Wales, the winter peak accounts for an additional 20 000 deaths per annum. It is likely that this reflects seasonal variations in risk factors. Seasonal variations have been demonstrated in a number of lifestyle risk factors such a physical activity and diet. However, a number of studies have also suggested a direct effect of environmental temperature on physiological and rheological factors. We review the available evidence on seasonal variations in coronary heart disease and possible explanations for them.