Oral contraception and other factors in relation to hospital referral for fracture. Findings in a large cohort study.

There is good evidence that estrogens and progestogens have an important effect on bone metabolism. This article explores the relationship between oral contraceptive (OC) use and fractures occurring at various sites among the 17,032 participants in the Oxford-Family Planning Association contraceptive study, which now includes information accumulated during 310,000 woman-years of observation between 1968 and 1994. In total, 1308 women suffered at least one fracture during the follow-up period, which was largely confined to premenopausal years. When all fractures were combined, there was a modest, but highly significant trend (p < 0.001) of increasing risk with total duration of oral contraceptive use. In addition, there was statistically significant heterogeneity (p < 0.01) when overall fracture rates were examined in relation to recency of oral contraceptive use during the premenopausal lifespan. The highest relative risk (1.3, 95% CI 1.1-1.5) was for current or recent oral contraceptive users; however, viewed as a whole, no clear pattern of risk was apparent. Examination of the data for individual fracture sites (including the lower end of the radius/ulna) did not provide any evidence of a protective effect of oral contraceptive use. These results are closely similar to those reported from the Royal College of General Practitioners Oral Contraception Study in 1993.