Hormonal IUDs increase risk of breast cancer nearly the same as hormonal pills, study finds

Women who use a hormone-releasing intrauterine device, or IUD, face around the same risk of breast cancer as women who take hormonal birth control pills, according to a new study.

The study, published Wednesday in JAMA Network, found that women who use levonorgestrel-releasing IUDs face an increased risk of breast cancer, an unexpected finding given that IUDs were thought to be lower risk.

The study looked at just over 78,000 women in Denmark between the ages of 15 and 49 who used levonorgestrel-releasing IUDs and compared them to the same number of women who did not use the devices.

Levonorgestrel, part of a class of medications called progestins, works by preventing the release of an egg from the ovary, according to the U.S. National Library of Medicine.

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In the study, women who used IUDs had a 40% higher chance of developing breast cancer than those women who did not, around the same risk level shown in other studies for women who take oral contraceptive pills. This translates to an estimated 14 more breast cancer cases per 10,000 women over five years.

Among women ages 15 to 49 in the U.S., approximately 14% of those using contraception take oral contraception pills and around 10% use long-acting devices like IUDs, according to data from the U.S. Centers for Disease Control and Prevention.

Hormonal IUDs work by delivering small amounts of hormones directly into the uterus.

It was thought previously that they provided a lower breast cancer risk than hormonal pills because they delivered smaller amounts of hormones into the uterus.

While taking hormonal birth control -- whether orally or through an IUD -- may raise the risk of breast cancer, the risk is small and must be weighed against the benefits of hormonal birth control individually, on a case-by-case basis. Women should talk with their health care provider.

Hormonal contraception has been shown to lower the risk of ovarian and uterine cancers, for example, but it is also shown to increase the risk of clotting.

In the U.S., around 1 in 8 women will be diagnosed with breast cancer in her lifetime, according to the CDC.