For the past several decades, women have been told that modern versions of hormonal birth control contain significantly lower doses of hormones and therefore did not carry the same pitfalls as their predecessors—pitfalls including a slightly increased risk of breast cancer. But according to a large study published Wednesday, even low-dose hormonal contraception raises women’s risk of getting breast cancer. Researchers followed 1.8 million women in Denmark for more than a decade, comparing women who used hormonal birth control and those who relied on nonhormonal methods such as condoms and copper IUDs. They found that women who used any kind of hormonal contraception still had a slightly elevated risk of breast cancer, similar to the risk of older forms of birth control. The longer the women used those methods, the higher their risk.
The new study is notable in part because it did not just track the effects of the pill, but also hormone-releasing IUDs, the birth-control patch, and other methods, which were all thought to be improvements on older methods thanks to the concentrated nature of how the hormones were released. As it turned out, the particular delivery method didn’t make much of a difference in the cancer risk. Many gynecologists assumed the lower doses of estrogen in newer generations of contraception would have lowered the risk of breast cancer, but this new research suggests that assumption is likely incorrect. (It’s also worth noting that the research, which was published in the New England Journal of Medicine, only showed an association and was limited in certain ways—the authors didn’t parse how other factors, such as physical activity or childbearing, might factor into the relationship, for instance.)
It’s always tricky to talk about studies like this one. A finding that has major implications for public health does not necessarily have major implications for personal health. And there are several reasons that women should not panic about these findings. First, the increase in the risk of any one birth-control user is vanishingly small. “A 20 percent increase of a very small number is still a very small number,” as one epidemiologist put it to NPR. Here’s how the New York Times explained it:
For a 20-year-old woman, for example, the probability of developing breast cancer in the next 10 years is .06 percent, or 1 in 1,732, according to breastcancer.org. Even if the relative risk increases 20 percent, it remains less than one-tenth of 1 percent. But by the time a woman reaches 40, her probability of developing breast cancer in the next 10 years is 1.45 percent, or 1 in 69. A 20 percent increase raises her risk to 1.74 percent, or 1 in 57.
Second, this study only investigated the chances that birth control increases one’s risk of breast cancer. But birth control does other things, too: The pill seems to lower the risk of endometrial and ovarian cancers, for example. If taking hormonal contraceptives comes with a slight uptick in breast cancer risk and a slight downtick in other cancer risks, that might be an even trade. And not for nothing, hormonal contraception also does a pretty spectacular job at lowering the risk of another major health problem for women: unplanned pregnancy. Medicine should not be assessed only by its rare side effects. Throwing your pill pack in the trash without a solid plan B could lead to, er, Plan B, which would have much more immediate and serious health consequences. When it comes to making your own personal health choices, you need to consider the entire set of benefits and risks—and stories like these can obscure that personal calculus. If you have concerns, the best thing to do is to bring them to your doctor and find the solution that’s the right fit for you, as an individual.
But zooming out to the public health level, this study is also an important reminder that women still bear the overwhelming responsibility for managing reproduction and the negative ramifications that come with it. Women research contraception. Women see their doctors about contraception. Depending who occupies the White House, women pay for contraception. Women set alarms and make appointments and pick up refill packs. Women read stories like this one, and call their doctors, and agonize about whether they should stay on the pill even if they have a family history of breast cancer, or try a new method—even though the pill has worked perfectly well for them for their entire reproductive lives. And all of that is not counting the work of actually bearing and raising children.
The promise of hormonal birth control for men has been researched for years, but has so far come to nothing. In the meantime, women will keep doing the math.