Scientists have linked hormonal contraceptives to an increased prevalence of breast cancer, according to a new study published Thursday.
Danish researchers found that “the risk of breast cancer was higher among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives,” according to the study, “Contemporary Hormonal Contraception and the Risk of Breast Cancer.” The risk increased with a longer duration of use, The New York Times reported Wednesday.
“However, absolute increases in risk were small,” the study noted.
The researchers followed 1.8 million women in Denmark between 15 and 49 years old for over a decade in order to evaluate associations between hormonal contraceptives and the risk of invasive breast cancer. None of the women had previously had cancer or had received treatment for infertility.
Compared to women who had never used hormonal contraceptives, the relative risk of breast cancer of those taking hormonal birth control was 1.20. This risk increased from 1.09 with less than a year of use to 1.38 with more than 10 years of use. Even after women stopped taking birth control, the risk of breast cancer was still higher among the women who’d been on hormonal birth control for five years or more.
The overall absolute increase in breast cancers diagnosed among current and recent users of any hormonal contraceptive was approximately one extra breast cancer for every 7,690 women using hormonal contraception for one year.
“This is an important study because we had no idea how the modern day pills compared to the old-fashioned pills in terms of breast cancer risk, and we didn’t know anything about I.U.D.’s,” said oncologist Marisa Weiss, according to the New York Times. “Gynecologists just assumed that a lower dose of hormone meant a lower risk of cancer. But the same elevated risk is there.”
“There was a hope that the contemporary preparations would be associated with lower risk,” David J. Hunter, a professor of epidemiology and medicine at the University of Oxford, said in an interview, the NYT reports. “This is the first study with substantial data to show that’s not the case,” he added.
The authors note their study is limited because they could not take into account factors like physical activity, breast-feeding and alcohol consumption, all of these may affect the risk of getting breast cancer.
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