A prospective study of oral contraceptive use and colorectal adenomas.

PURPOSE: The influence of reproductive factors on colorectal cancer, including oral contraceptive (OC) use, has been examined, but less research is available on OC use and adenomas.

METHODS: Participants of the Nurses' Health Study who had a lower bowel endoscopy between 1986 (when endoscopies were first assessed) and 2008 were included in this study. Multivariable logistic regression models for clustered data were used to estimate odds ratios and 95 % confidence intervals [OR (95 % CIs)].

RESULTS: Among 73,058 participants, 51 % (n = 37,382) reported ever using OCs. Ever OC use was associated with a slight increase in non-advanced adenomas [OR 1.11, 95 % CI (1.02, 1.21)] but not with any other endpoints. Duration of OC use was not associated with adenomas, but longer times since last OC use were associated with increased odds of adenomas [e.g., compared to never use, 15+ years since last use: OR 1.17 (1.07, 1.27)]. Shorter times since last OC use were inversely associated [e.g., ≤4 years since last use: OR 0.74 (0.65, 0.84)].

CONCLUSIONS: We observed a modest borderline increase in risk of colorectal adenomas with any prior OC use. Additionally, more recent OC use may decrease risk, while exposure in the distant past may modestly increase risk of adenomas.