Background: Various studies have reported an inverse relation between oral contraceptive (OC) use and the risk of colorectal cancer, but the issue is still open.
Methods: In order to quantify the association between OC use and colorectal cancer risk, we performed a systematic review and meta-analysis of studies on this issue. We identified all relevant studies published, in English, as original articles up to December 2008 through a search of the literature using PubMed and EMBASE, and by reviewing the references from the retrieved articles.
Results: The summary relative risk of colorectal cancer for ever versus never OC use was 0.82 (95% confidence interval, CI, 0.69-0.97) from 11 case-control studies, 0.81 (95% CI, 0.75-0.89) from seven cohort studies, and 0.81 (95% CI, 0.72-0.92) from all studies combined. The results were similar for colon and rectal cancer. No difference was evident according to duration of OC use both for colon and rectal cancer, although there is an indication that the protection is stronger for more recent use (OR = 0.70, 95% CI, 0.53-0.90, on the basis of four studies).
Conclusion: Epidemiological data consistently indicate that OC users have a reduced risk of colorectal cancer, and that the protection is greater for recent use in the absence, however, of a duration-risk relation.