Women using birth control pills and I.U.D.s that release
hormones face a higher risk than those using methods
without hormones, scientists in Denmark reported.
Women who rely on birth control pills or contraceptive devices that release hormones face a small but significant increase in the risk for breast cancer, according to a large study published on Wednesday.
The study, which followed 1.8 million Danish women for more than a decade, upends widely held assumptions about modern contraceptives for younger generations of women. Many women have believed that newer hormonal contraceptives are much safer than those taken by their mothers or grandmothers, which had higher doses of estrogen.
The new paper estimated that for every 100,000 women, hormone contraceptive use causes an additional 13 breast cancer cases a year. That is, for every 100,000 women using hormonal birth control, there are 68 cases of breast cancer annually, compared with 55 cases a year among nonusers.
While a link had been established between birth control pills and breast cancer years ago, this study is the first to examine the risks associated with current formulations of birth control pills and devices in a large population.
The study found few differences in risk between the formulations; women cannot protect themselves by turning to implants or intrauterine devices that release a hormone directly into the uterus.
The research also suggests that the hormone progestin — widely used in today’s birth control methods — may be raising breast cancer risk.
“This is an important study because we had no idea how the modern day pills compared to the old-fashioned pills in terms of breast cancer risk, and we didn’t know anything about I.U.D.’s,” said Dr. Marisa Weiss, an oncologist who founded the website breastcancer.org and was not involved in the study. “Gynecologists just assumed that a lower dose of hormone meant a lower risk of cancer. But the same elevated risk is there.”
“It’s small but it’s measurable, and if you add up all the millions of women taking the pill, it is a significant public health concern,” Dr. Weiss added.
The study was limited, the authors said, because they could not take into account factors like physical activity, breast feeding and alcohol consumption, which may also influence breast cancer risk.
Officials with the American College of Obstetricians and Gynecologists said that they would carefully evaluate the new findings, but emphasized that hormonal contraceptives are for many women “among the most safe, effective and accessible options available.”
Experts noted that oral contraceptives have some benefits as well, and are associated with reductions in ovarian, endometrial and possibly colorectal cancers later in life.
Dr. Chris Zahn, A.C.O.G.’s vice president for practice activities, acknowledged a link between breast cancer risk and hormone use, but urged concerned women to consult a trusted medical provider before making changes. “It’s important that women feel confident and comfortable with their contraceptive choice,” he said.
Because risk increases with age, Dr. Weiss suggested that older women may want to consider switching to a hormone-free birth control method, like a diaphragm, an I.U.D. that does not release hormones, or condoms. “It’s not like you don’t have a choice,” she said. “Why not pursue another option?”
In a commentary accompanying the new study, which was published in the New England Journal of Medicine, David J. Hunter, a professor of epidemiology and medicine at the University of Oxford, said the new study did not find that any modern contraceptives were risk-free.
“There was a hope that the contemporary preparations would be associated with lower risk,” he said in an interview. “This is the first study with substantial data to show that’s not the case.”
Nearly 10 million American women use oral contraceptives, including about 1.5 million who rely on them for reasons other than birth control. The number of women in the United States with intrauterine devices, many of which release hormones, has grown in recent years, as has the number of women using other types of hormonal contraceptive implants.