We have known for quite some time that oral contraception helps prevent ovarian cancer. Why does this work? In a nutshell, the theory holds that there is some trauma to the ovarian surface every time an egg is released. Oral contraceptives stop this release. The overall mechanism is much more complex than that, but incompletely understood. Nevertheless, the question has always been, how long does this protective effect last?

Researchers from Oxford University in England performed an extensive review of the medical literature and used a process called meta-analysis to meaningfully combine a very large overall number of women who had been on the pill versus those who were not users. Forty five studies from 21 countries accounted for almost 24 thousand women with ovarian cancer compared with 87 thousand who did not. In those women who used the pill, the average length of oral contraceptive use was approximately 5 years.

The results showed that for every five years of use there was a 20% decrease in risk. Those women who were on the pill for 15 years or so were 50% less likely to develop ovarian cancer and this risk reduction continued for 30 or more years after use was discontinued. The researchers also looked at the differences between oral contraceptive doses, which have substantially decreased over the last 40 years, and found no difference. There was a small short term increased risk of breast cancer, but this was not persistent after discontinuation of the pill.

Bottom line: Taking oral contraception for five years or more offers long lasting protection against ovarian cancer, according to this review.

Source: Beral V et al. Lancet 2008;371:303-314