Oral contraceptives and other risk factors for gallbladder disease
Prior studies of the association between oral contraceptives (OCs) and gallbladder disease (GBD) have yielded conflicting results. To clarify this association, a retrospective (historical) cohort study was performed on a very large data base including 1980 and 1981 Medicaid billing data from the states of Michigan and Minnesota in which 138,943 users of OCs were compared with 341,478 nonusers. The crude relative risk (RR) and 95% confidence interval (CI) for symptomatic GBD resulting in medical care was 1.14 (CI 1.09 to 1.20), with a clear dose-response (P < 0.001). Age markedly modified the effect of OCs on GBD. The RR (CI) decreased from 3.1 (2.7 to 3.6) in women 15 to 19 years old to 1.2 (0.9 to 1.5) in women 40 to 44 years old, providing an explanation for previously conflicting reports. The effects of a number of other risk factors on GBD, some which have been controversial, were also confirmed. Adjustment for these did not change the results. In conclusion, OCs are risk factors for GBD, although the risk is of sufficient magnitude to be of potential clinical importance only in young women.