A new study, published in the British Medical Journal of Clinical Pharmacology, analyzed data from nearly 2,500 Danish women between the ages of 15 and 49. Of those women, 317 had glioma, a rare brain tumor. (And when we say “rare,” we mean it. Approximately 5 women in 100,000 are diagnosed with the cancer annually in the Danish population, according to lead study author David Gaist, MD, PhD, neurology professor at the University of Southern Denmark’s Institute of Clinical Medicine. Only 4 in 100,000 US women are.) Researchers found that women who had ever used any type of hormonal contraceptive—birth control pills or IUDs—were 1.5 times more likely to develop gliomas than those who had never used hormonal contraceptives. That risk increased with duration of use: women who had taken birth control for five years or more were almost 2 times more likely to develop the rare cancer, nearly doubling the rate of diagnosis to 10 in 100,000. The certain type of birth control factored into the risk, as well. Research showed that women taking progestin-only pills (mini-pills) had a higher risk for developing the brain cancer than women with IUDs or on combination pills (those containing estrogen and progestin). Though there’s no concrete proof about why mini-pills caused an increased risk in brain cancer rates, researchers speculate that a woman’s BMI could have an effect, as progestin-only pills are most commonly prescribed to overweight women. But before you go cold turkey on your birth control, take into account that the study only found an association between the use of hormonal contraceptives and risk of glioma, and therefore can’t suggest a true cause-and-effect relationship. And according to Audrey Lance, MD, an assistant professor in the department of obstetrics, gynecology, and reproductive sciences at Magee-Womens Hospital of University of Pittsburgh Medical Center, the benefits of birth control still outweigh any possible risks. The rarity of gliomas should also be taken into account, despite the nearly doubled risk. “When you say something doubles your risk it sounds very scary, but doubling what’s already a very small risk still equals a very small risk,” says Lance. Overall, the recent study doesn’t indicate any need for women to question or change their current or past birth control use, she says. But if worries persist, consult your gynecologist before making any medical decisions. MORE: The Future of Birth Control: Remote Control Fertility?
