Do all contraceptives lower ovarian cancer risk?

Birth control pills have long been known to reduce the risk of ovarian cancer, but a new study suggests any type of contraceptive - even, surprisingly, vasectomy - may also be protective.

After comparing women with ovarian cancer to those without, researchers found that women who used any type of contraception - birth control pills, tubal ligation (getting your "tubes tied"), intrauterine devices (IUDs), barrier method (such as diaphragms) or male vasectomy - had between a 40 and 65 percent lower risk of ever developing ovarian cancer.

It's not a surprise to see an association between birth control pills and ovarian cancer, and even to see one for tubal ligation, since other studies have shown the same thing, study author Dr. Roberta Ness of the University of Texas School of Public Health told Reuters Health.

But to see a similar trend for women who relied on IUDs, the barrier method, or a partner's vasectomy to avoid pregnancy is somewhat surprising, Ness acknowledged.

"No matter what method of contraception you use, it looks like that would be protective."

More than 21,000 U.S. women will develop ovarian cancer in 2010, and another 14,000 will die from it. Approximately 1.4 percent of women will develop ovarian cancer in their lifetimes.

Given that some forms of contraception are associated with a lower risk of ovarian cancer, Ness and her team set out to see whether all types had any impact on the future risk of disease.

They interviewed 869 women who had developed ovarian cancer, and 1779 others who had not developed the disease, about their history of contraception. Women were considered to use no artificial contraception if they relied on natural family planning (avoiding sex during ovulation) or withdrawal.

As expected, women who had gotten their tubes tied or taken birth control pills in the past, either for contraception or other reasons, were less likely to have developed ovarian cancer, they reported in the journal Annals of Epidemiology.

But strangely, so were women who used an IUD. Specifically, women who developed ovarian cancer were less likely to have ever used an IUD - among those with cancer, only 12 percent had ever used an IUD, versus 17 percent of women who did not develop the cancer.

Similarly, 14 percent of those with ovarian cancer had a partner who had undergone a vasectomy, but so did 17 percent of the women who never developed ovarian cancer.

After using statistical tools to remove the influence of factors that could affect the relationship between contraception and cancer, Ness and her team found that relying on a vasectomy or IUD lowered women's risks of ovarian cancer by 50 and 60 percent, respectively, relative to women with no history of artificial contraception.

The big question is: why? It's possible that sperm itself may increase inflammation when inside a woman, and this inflammation could, over time, increase her risk of ovarian cancer, Ness suggested. Any technique that reduces a woman's exposure to sperm - vasectomy, tubal ligation, or IUDs - would therefore potentially protect women from that inflammation, she said.