The data for the study was collected from 1.8 million Danish women for more than a decade.
The bottom line is that before starting or continuing to take hormonal contraceptives - or any medications - it's important to speak with your doctor about any potential risks and benefits, and make an informed decision from there. But, the overall risk remains small, and past research suggests oral contraceptives protect against other types of cancer. What's more, other studies have found that taking hormonal birth control may actually reduce the risk of other cancers, including ovarian cancer, endometrial cancer and colorectal cancer, they said.
Those dangers are somewhat offset by reduced risks of cancer - of the ovaries, endometrium, and digestive system - that other studies have linked to birth control pills, according to David Hunter, an Oxford University epidemiologist who wrote a commentary on the study.
The study found few differences in risk between the formulations; women can not protect themselves by turning to implants or intrauterine devices that release a hormone directly into the uterus. After all, it means that almost a quarter of American women are doing something that might increase their risk of developing breast cancer by a third-in theory. "But the same elevated risk is there". What they should know, however, is that the longer they take them, the greater the chance they will develop breast cancer.
But the study did not account for some other things that affect breast cancer risk, including physical activity levels and alcohol consumption. "The range of risks we're talking about here is much much smaller", she said. "It's not like you don't have a choice", she said.
Results were published Wednesday in the New England Journal of Medicine.
"There was a hope that the contemporary preparations would be associated with lower risk", he said in an interview.
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.
Once women stopped using these forms of birth control, the increased risk of breast cancer disappeared if the women had used hormonal contraception for less than five years.
Though the older oral contraceptives were known to increase the risk of breast cancer, many doctors and patients had assumed the newer generation of pills on the market today were safer.
One thing reiterated by every doctor Newsweek spoke to: Women who are anxious about how their contraception might increase their risk of breast cancer should speak with their health care provider. "It is a very clear picture for us, very convincing". During that time period, 11,517 cases of breast cancer were identified. Still, the additional risk would result in a comparatively few additional cases of breast cancer, the researchers said.
For some perspective, about 252,710 American women were diagnosed with breast cancer in 2017, according to estimates from the National Institutes of Health; 12.4 percent of women will hear the diagnosis at some point in their lives. The illness is fairly rare among women in the age group studied.
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.