Many publications have claimed that oral contraceptives (OCs) are associated with an increased risk of circulatory disease, yet between the years 1962 and 1976, when OCs became widely used in the United Kingdom, death rates from circulatory disease in women of reproductive age fell steadily. This decreased mortality was greater in young women than in men of comparable age, and did not occur in older women. These data tend strongly to refute the belief that OCs are causative of circulatory disease. The possibility that the decreased mortality rate is due to a protective effect of OCs was examined. It was concluded that they could not be completely responsible, although a partial effect could not be ruled out with certainty. It is suggested that, when mortality trends are opposed to the results of case-control or cohort studies, serious doubts are cast on the conclusions about causal relationships.
PIP: It is claimed that OCs (oral contraceptives) are causally associated with diseases of the circulation, and in particular with thromboembolism and myocardial infarction. OCs are now used by about 1/3 of women in the United Kingdom; thus, according to what is claimed in many epidemiological studies, the incidence of mortality should have shown the effects of OC introduction and increasing use. This study shows that, although the sales of OCs have risen from 0 in 1961 to 45 million packets in 1976, the incidence of circulatory mortality in 15-44 year-old women has fallen by 34% since 1962. It is difficult to reconcile these data with the hypothesis that OC use is causally related to circulatory disease mortality. Such findings, moreover, are not confined to the United Kindgom. The hypothesis that OCs are actually protective against circulatory diseases is attractive; there is, however, no evidence to support it.