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. But they stress there is no need for most women to abandon birth control pills for fear of breast cancer.
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.
Specifically, the study found that it may be the hormone progestin - a key component of many of today's hormonal contraceptives - that is behind the breast cancer risk.
"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".
Breast cancer is the second-biggest cancer killer of American women, after lung cancer.
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.
Older contraceptives were known to carry a higher risk of breast cancer, but doctors had hoped that the newer lower-estrogen formulations might pose a lower risk.
They found that women taking estrogen/progestin birth control pills have about a 20 percent increased risk of breast cancer.
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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". "Depending on their reasons for using oral contraceptives, they might want to consider other options, including non-hormonal contraceptives". But he suggested doctors take time to discuss the pros and cons of different types of contraception with their patients, and that they be frank about the potential risks, suggesting women reassess hormone use as they age.
A hormone specialist at Brigham and Women's Hospital who deals with contraceptive issues says the study shouldn't alarm those taking oral contraceptives. "That's not necessary and not supported by the data", said Dr. Roshni Rao, chief of breast surgery at New York - Presbyterian/Columbia University Medical Center in New York City, who was not involved with the study.
"The increased risk also with newer progestins in hormonal contraceptives has not been shown consistently before, though progestins in postmenopausal therapy has also been found to increase the risk of breast cancer", she added. By contrast, there was no increased risk for breast cancer seen in women who used hormones for less than one year.
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 relative risk increase in this study is only 1.2 on average".
"That is a very small extra risk. The risk of dying when you're pregnant is probably higher". 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.
Women who stayed on hormones for 10 or more years experienced a 38 per cent increase in their relative risk of developing breast cancer, compared with nonusers.
Such alternatives include a copper IUD, condoms or, if women are done having children, tubal ligation.