Published: Thu, December 07, 2017
Medicine | By Earnest Bishop

We Now Know More About the Link Between Birth Control & Breast Cancer

We Now Know More About the Link Between Birth Control & Breast Cancer

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.

Now a big study from Denmark suggests the elevated risk of getting breast cancer - while still very small for women in their teens, 20s and 30s - holds true for these low-dose methods, too. 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. Yet the new study found increased risks that were similar in magnitude to the heightened risks reported in earlier studies based on birth control pills used in the 1980s and earlier, Hunter said.

The study of nearly 2 million women in Denmark looked at women using birth control methods such as the pill, NuvaRing, or implants. Researchers using the approach often lose contact with some patients, and conducting such studies often cost "a fortune", Morch said.

While contraceptive drugs that contain oestrogen have always been suspected of increasing the likelihood of breast cancer, researchers had expected smaller doses of the hormone, often combined with the drug progestin, would be safer, said Lina Morch, an epidemiologist at Copenhagen University Hospital who led a study analysing the records of 1.8 million women in Denmark. However, that number varied depending on how long women had used their particular method.

That may sound scary. But the odds rose among women who used hormonal contraception for more than 10 years, the study found.

First, the study didn't factor in other variables like diet, physical activity, breastfeeding or alcohol consumption, which could also have an impact on developing breast cancer.

"The absolute increase in risk [found in the study] is 13 per 100,000 women overall, but only 2 per 100,000 women younger than 35 years of age", writes epidemiologist David Hunter, of the University of Oxford, in an editorial accompanying the study in NEJM.

Almost 10 million American women use oral contraceptives, including about 1.5 million who rely on them for reasons other than birth control.

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Any additional risk of breast cancer, he says, should be weighed against the clear benefits of hormonal contraception - benefits that go beyond the obvious advantages of preventing unwanted pregnancy.

The increase in breast cancer cases associated with hormones was also small because young women are at low risk to begin with. 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.

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There are also numerous potential health benefits of hormonal contraceptives beyond preventing pregnancy, including decreasing the risk of endometrial, ovarian and colorectal cancers, as well as helping with menstrual cycle regularity, migraines and acne.

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".

Those who used them for longer periods were at even greater risk. But researchers in Denmark looked at 1.8 million women between the ages of 15 and 49 to see if new lower-dosed formulations are still risky.

At mbg, we've been asking questions about the birth control pill for years. Epidemiologist Lina Morch headed the study.

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.

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