The Pill Prevents ... Colorectal Cancer?
April 19, 2001 -- The Pill may prevent more than just pregnancy. Combined findings from several studies point to a lower risk of colorectal cancer in women who have used oral contraceptives.
According to a report in the British Journal of Cancer, women who took birth-control pills at any time in their lives were less likely to get colorectal cancer than women who never used oral contraceptives.
"The finding was significant: [the level of] protection was about 20%," study co-author Carlo La Vecchia, MD, tells WebMD.
It didn't matter how long women took birth-control pills -- just having used them seemed to offer protection. However, the women who took the pills most recently seemed to have the most protection -- their colorectal-cancer risk was cut in half.
"We saw a stronger risk reduction -- about 50% -- for recent use, that is, for women who had stopped using the pill in the last 10 years," La Vecchia says. "This is often seen for hormonal effects. [For example], the recency effect is almost always seen for hormone replacement therapy, which is thought to protect against colorectal cancer. Also, birth-control-pill users are young women and you don't see a lot of colorectal cancer in women aged 20-40, so that also contributes to the recency effect."
La Vecchia, director of the Mario Negri Institute for Pharmacological Research in Milan, Italy, and co-workers analyzed data from 12 previous studies of colorectal-cancer risk factors. Eight of these studies compared colorectal-cancer patients to closely-matched healthy people. Four of the studies followed women over time and compared those who got colorectal cancer to those who did not.
Duke University researcher Dawn Provenzale, MD, is an associate professor of gastroenterology. She did not participate in the Italian study. "Probably a lot of people don't know about this," she tells WebMD. "There is some suggestion that postmenopausal hormone replacement therapy reduces cancer risk, but this study about oral contraceptives provides an interesting addition to the literature."
A clue to what may be going on comes from other recent studies. La Vecchia notes that in the test tube, the female sex hormone estrogen -- a principal ingredient of birth-control pills -- makes it hard for colorectal-cancer cells to grow. And estrogen has other effects on the digestive system as well.
"When you have [this kind of indirect] finding, you may find several interpretations," La Vecchia says. "What we are trying to say is that the observation has a biological possibility. We don't know the exact mechanism."
The new report isn't proof that oral contraceptives protect against colorectal cancer. La Vecchia warns that dietary factors are probably far more important than hormones. But it does add to a growing body of evidence that birth-control pills have more health benefits than disadvantages.