Oral contraceptive pill use and fractures in women: a prospective study.

It has been suggested that use of the oral contraceptive pill by women confers protection against osteoporosis later in life. However, cross-sectional studies of bone density among pill users have yielded discrepant results. We therefore investigated the relationship between pill use and subsequent occurrence of fracture in a cohort of 46,000 women enrolled in the Royal College of General Practitioners Oral Contraception Study during 482,083 person-years of follow-up. Fracture risk was lower among multiparous women, non-smokers, and those of lower socio-economic class. The risk of subsequent fractures among the women who had ever used the oral contraceptive pill was significantly greater than that among women who had never used it (relative risk 1.20, 95% confidence intervals 1.08-1.34) after adjustment for these variables. When the analysis was confined to forearm fractures, no significant effect of pill use on fracture risk was detected. Although the study only includes limited observation of older women to date, these data do not support the hypothesis that pill use protects women against the occurrence of osteoporotic fractures in later life.