The intrauterine device (IUD) is considered one of the most effective and long-lasting forms of birth control available. Now a new study suggests it may also have a role in preventing cervical cancer.

A new analysis of available research suggests that women who use an IUD are about 30% less likely to get cervical cancer than women who don’t use the contraceptive method.

The findings are still very early, and women should not make any birth control decisions based on their study alone, according to the researchers of the new report, published Tuesday in the journal Obstetrics & Gynecology. “This is observational research so we are always skeptical,” says study author Victoria Cortessis, an associate professor of clinical preventive medicine at the Keck School of Medicine of USC. For now, Cortessis says, women should not get an IUD for the sole purpose of preventing cervical cancer. There are other reasons to consider the device, including its effectiveness as a contraceptive.

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Still, Cortessis says that the link between the IUD and a lower risk for cervical cancer is a trend she’s been following through the years, and decided there was enough available evidence to take a closer look. “I would be shocked if it’s not a real phenomenon,” she says.

In the study, Cortessis and her co-authors analyzed 16 observational studies of 12,000 women from around the world and found that among women using an IUD, the incidence of cervical cancer was much lower.

Almost all cervical cancers are caused by the human papillomavirus (HPV), which has become a very common STD in the United States (nearly all men and women will get at least one type of HPV during their lifetimes). Most of the time HPV infections go away on their own, but sometimes they can develop into cancer. In 2014—the most recent data available—12,578 American women were diagnosed with cervical cancer. In 2012, there were an estimated 530,000 new cases worldwide, and 90% of the women who died from the disease lived in low and middle income countries.

“This is a horrible epidemic in the developing world,” says Cortessis.

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How an IUD might prevent cervical cancer or help clear an HPV infection is unknown, but there are a few prominent theories, Cortessis says. It’s possible that getting an IUD spurs immune system attention to the area where the IUD is placed, which is also where cervical cancer cells congregate. When a woman gets an IUD, the immune system may target the area since there is now a foreign body present. This may help clear an infection or help bolster the body’s response to infections in the area. There’s also the suggestion that when an IUD is removed, some cervical cells that contain HPV infection are scraped off, though Cortessis says she’s more skeptical of that theory.

“We need to figure out what’s going on mechanistically and do some fine tuning and see what kind of use could prevent cervical cancer and integrate that with contraceptive counseling,” says Cortessis, adding that a lot more research is needed, including determining if the effect is real and whether all IUDs provide the lower risk.

Since Cortessis and her co-authors looked at data from already completed studies, they do not know for certain what type of IUD women were using, since not all the studies provided that information. However, Cortessis says that her team can confidently say that most women in their report were using non-hormonal IUDs, based on when the studies the were conducted and the available IUDs during that time. Whether the type of IUD matters will also need to be studied.

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