Cardiovascular disease is the most common cause of death in most developed countries, but mortality is particularly high in some parts of Britain. These high rates can be lowered only if the causes are understood. Preventive campaigns have concentrated on smoking, hypertension, and hyperlipidaemia. These risk factors explain at most half of all myocardial infarctions.1

Deaths and hospital admissions for coronary heart disease and stroke are higher in winter than in summer in many temperate countries.2 In some winters mortality has been as much as 70% higher than in the summers. The size of the winter excess is related to the difference in environmental temperature. Excess winter cardiovascular mortality has fallen in recent years, but it remains numerically far more important than other causes of winter deaths such as respiratory infections or hypothermia.3 Seasonal fluctuations in cardiovascular events are greater in Britain than in some other countries with wider temperature variations and colder winters, and this suggests that the excess winter deaths may be preventable.2 Lesser seasonal variations may be related to more constant indoor temperatures in those countries. In Britain excess winter mortality is greatest in socially deprived people who have the worst domestic heating and the highest overall mortality.

Seasonal variations in vascular events do not necessarily result in an increase in annual mortality. Deaths …