Chances are you've heard about the link between birth control and breast cancer. While a body of research suggests that oral contraceptives can lead to a slight increased risk of breast cancer, studies also show that this risk disappears after you've been off the pill for ten years, and still other research found no significant increase in risk.
Now, new data points to the role of estrogen in birth control pills as a key mediator in this link. Women who recently took birth control pills with high doses of estrogen had an increased risk of breast cancer, according to a recent study published in the journal Cancer Research.
For this latest study, scientists at the Fred Hutchinson Cancer Research Center and the University of Washington in Seattle looked into the pharmaceutical records of 1,102 women diagnosed with breast cancer—and compared the formulations of birth control they filled in the past year with those that 21,952 breast cancer-free women had been filling.
They divided up birth control prescriptions into three categories: Those formulated with low levels of synthetic estrogen (about 20 micrograms of ethinyl estradiol), those with moderate levels (30 to 35 micrograms of ethinyl estradiol or 50 micrograms of mestranol) and those with high levels (about 50 micrograms of ethinyl estradiol or 80 micrograms of mestranol).
The researchers found that the women who took high-estrogen pills in the past year were 2.7 times more likely to have breast cancer, while those who took moderate-estrogen pills in the past year were about 1.6 times more likely to develop the cancer. Low-dose pills, however, did not increase their breast cancer risk.
What gives? The female sex hormone estrogen is known to stimulate breast tissue growth, and researchers believe the doses and types of estrogen in birth control pills may impact whether or not that growth develops into cancer. Progestins, also found in combination birth control pills, may play a role as well.
So How Worried Should You Really Be?
While these new findings sound scary, they basically echo much of the previous research, including an analysis of data in 2010, which looked at over 116,000 women and found that those who used oral contraceptives had a slight increased risk of breast cancer. However, it's important to remember that the study focused on oral contraceptives that had been taken in the past year, so this may not be the case for women who have stopped taking the Pill. A global review of 54 studies in 1996 found that the increased risk of breast cancer disappears after being off the Pill for 10 years.
Plus, very few high-dose estrogen pills currently exist, says lead study author Elisabeth F. Beaber, Ph.D., M.P.H., a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle. In fact, by the last phase of this study, which took place from 2005 to 2009, only half of one percent of women were using the high-dose pills.
Why? While they were common 20-plus years ago, advances in birth control have helped create new "lowest effective doses," which carry fewer potential side effects, such as blood clots, says ob-gyn Alyssa Dweck, M.D., coauthor of V is for Vagina. Now, high-dose pills are typically only prescribed when nothing else works at regulating a woman's cycle or she has possible drug interactions, says Dweck. For instance, patients on anti-seizure medications may be prescribed high-dose birth control pills, since anti-seizure medications can decrease the effectiveness of lower-dose ones.
For most women, though, the biggest downside to taking a low-dose pill is the potential for breakthrough bleeding. And while they are just as effective at preventing pregnancy as high-dose pills when taken correctly, a missed low-dose pill could result in a higher risk of pregnancy than if you were taking one with a greater dose of hormones. Dweck recommends talking to your doctor to see if a low-dose pill is right for you. You can always start with the lowest-dose pill available and tweak the dose or brand as needed until you find the right one for you.
Whatever your formulation, Beaber and Dweck both agree that, for many women, the health benefits of birth control pills still outweigh the risks. While, according to the American Cancer Society, a woman's risk of developing invasive breast cancer is 1 in 8 (and dying from it, 1 in 36), that risk is even lower for young women. Plus, when taken for 15 years, the pill can slash your risk of ovarian and endometrial cancers by about 50 percent, according to one 2010 study. Meanwhile, it can also ease symptoms of polycystic ovary syndrome and endometriosis, both of which can threaten fertility—and each affect an estimated 10 percent of women. The potential health benefits are so strong that one 2011 Guttmacher Institute survey found that 14 percent of women use the pill exclusively for reasons other than preventing pregnancy.
In the end, Beaber says more research is needed before doctors switch the scripts they're prescribing. But if you're worried about your risk of breast cancer while on the Pill, it can't hurt to ask your doc about your dosage.