Birth control may be putting women at risk for breast cancer

Katherine Streeter for NPR

Enlarge this image Katherine Streeter for NPR Katherine Streeter for NPR

It's always been known that hormonal contraception, like any medicine, carries some risks. A study published Wednesday has linked newer-generation birth control pills with breast cancer; the link had already been established for older variants of hormonal contraception.

Morch's team pored through years of electronic health records collected by the Danish health system, using prescription data to identify which women had taken the drugs and then track their health outcomes.

At mbg, we've been asking questions about the birth control pill for years.

What really surprised the researchers was that the increased risk was not confined to women using oral contraceptive pills, but also was seen in women using implanted intrauterine devices, or IUDs, that contain the hormone progestin. Researchers using the approach often lose contact with some patients, and conducting such studies often cost "a fortune", Morch said. The results, however, showed that for every 100,000 women, the use of a hormone contraceptive causes an additional 13 cases of breast cancer each year.

Dr Chris Zahn, ACOG'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.

In fact, birth control increases breast cancer risk about as much as drinking alcohol does, said Dr. Mary Beth Terry, an epidemiologist at the Columbia University Mailman School of Public Health.

The increase in breast cancer cases associated with hormones was also small because young women are at low risk to begin with. The findings indicate that the hormone progestin is adding to breast cancer risk; some of the contraceptive pills and numerous IUDs included only progestin, Mørch said. "But the same elevated risk is there". The study's published in The New England Journal of Medicine, and NPR's Patti Neighmond has our report.

Lindegaard speculated that the hormones in birth control may trigger certain cells that are ready to turn into cancer, he said, given that the risk seems to increase after only a few months of use.

The study, which used all of Denmark as its sample, followed almost 1.8 million women of childbearing age for over a decade on average, drawing data from national prescription and cancer registries. Epidemiologist Lina Morch headed the study.

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Compared to what the group of researchers found in one of their other papers-that using hormonal contraception was associated with a 300 percent increase in suicide risk-"it is a modest increase", said Dr. Øjvind Lidegaard, one of the authors of the paper and a gynecologist at the University of Copenhagen.

NEIGHMOND: Hormonal contraception releases estrogen, progestin or a combination of both to suppress ovulation and prevent pregnancy.

Of course, finding a safe and effective form of birth control is more than just a personal concern.

MIA GAUDET: Including the patch, the ring, the implant, as well as IUD.

"In the 1980s and 1990s, there was some optimism regarding the development of a formulation that would reduce a woman's risk of breast cancer", he said in the commentary, "but research into this possibility appears to have stalled". What they should know, however, is that the longer they take them, the greater the chance they will develop breast cancer. The hope was the lower dose would decrease breast cancer risk. "But we should make an individual assessment-doctor and a woman, together-to see what is the most appropriate thing for her to use".

NEIGHMOND: Lead researcher Morch says the findings should serve as a caution but not an alarm.

Overall, there was one extra case of breast cancer for every 7,600 women using hormonal contraception for a year.

MORCH: So it has to be balanced - the pros and cons of these contraceptives. About 40,000 women died of breast cancer in 2017.

HUNTER: There's very good evidence that oral contraceptives reduce the risk of ovarian cancer.

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