A large December 2017 study published in The New England Journal of Medicine (NEJM) found that women who used hormonal birth control had a 20 percent increased risk of breast cancer. While past studies have confirmed a link between the disease and older forms of hormonal contraception, the NEJM study sheds light on newer forms, which experts believed would be safer.
It's estimated about 10 million American women use birth control pills, and millions more use other hormonal contraceptives, like injections and IUDs. And while this study may be alarming to many, it's important to note how it was conducted, and what it really means in terms of your breast cancer risk.
How the study was done
Researchers followed 1.8 million Danish women between the ages of 15 and 49 for about 11 years, tracking their use of hormonal birth control, including pills, patches, vaginal rings, certain IUDs and Plan B (the morning-after pill). To reach their conclusions, they did not include women who had been treated for infertility, or who had a previous diagnosis of cancer or venous thromboembolism.
There were limits to the study in that researchers considered some risk factors for breast cancer—including childbirth, education and family history—but not others. They did not adjust for alcohol consumption or physical activity, for example.
What they found
During those 11 years, there were 11,517 cases of breast cancer among the Danish women. Overall, those who currently or recently used hormonal contraceptives were 20 percent more likely to be diagnosed with the disease than those who didn't.
It appeared that the longer women were on hormonal birth control, the greater their chances of breast cancer. Their risk increased by 38 percent if they had been using a hormonal contraceptive for more than 10 years, but rose by only 9 percent if they used it less than a year. If women used it at least five years and then stopped, their chances remained elevated five years later.
Breast cancer risk also differed by age. Most of the increase occurred in women in their late 30s and 40s, and there was very little raised risk for women under age 35. Breast cancer risk peaks between the ages of 50 and 70, and past hormonal birth control use is thought to have little lasting impact at this age.
What that really means
While the statistics may seem dire at first, they should be considered in terms of absolute numbers—or, how many more women are diagnosed with breast cancer each year. That 20 percent increase works out to about 13 additional women per every 100,000.
In other words, for those aged 15 to 49 who didn't use hormonal birth control, there were about 55 cases of the disease for every 100,000 women. For those who did, the incidence was 68 per 100,000. It's 1 additional diagnosis for every 7,690 women.
What's more, the raised breast cancer risk largely affected women 35 and older—mostly in their 40s. For women under 35, whose odds are very low to begin with, the increase worked out to just 1 additional case per 50,000 women.
What that means for you
Ultimately, younger women using hormonal birth control should have little reason to panic. Though the American College of Obstetricians and Gynecologists (ACOG) is said to be considering the study's results, representatives noted hormonal birth control is still considered safe and effective for many women. Not only does it prevent pregnancy, but it's thought to lower your risk of some cancers, including ovarian, endometrial and colorectal cancer.
While the breast risk remains relatively low, women in their 40s or women genetically predisposed toward breast cancer may want to discuss other options for birth control with their doctor. These may include condoms or copper (non-hormonal) IUDs, or even vasectomies.
The bottom line? Whether you're on hormonal birth control or thinking of starting, speak with your OBGYN to weigh the risks and advantages, especially if you're in your late 30s or older.
