Modern birth control pills that are lower in estrogen modestly raise the risk of breast cancer, especially with long-term use, a Danish study found.
Researchers discovered a similar breast cancer risk with the progestin-only intrauterine device, and they could not rule out a risk for other hormonal contraceptives like patches and implants.
However, the overall increased risk was small, amounting to one extra case of breast cancer among 77,000 women using contraceptives per year.
Experts warned women should balance the study’s findings against the benefits of the pill, which includes a lower risk of other cancers.
"Hormonal contraception should still be perceived as a safe and effective option for family planning," said Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital, who was not involved in the research.
Manson suggested women in their 40s should consider using non-hormonal IUDs, getting their tubes tied or talking with their partners about a vasectomy.
Studies of older birth control pills have shown “a net cancer benefit” because of the lowered risk of cancer of the colon, uterus and ovaries despite a raise breast cancer risk, Mia Gaudet, a breast cancer epidemiologist at the American Cancer Society, said.
There was optimism that newer, low-dose contraceptives would lower the breast cancer risk, but these results have dashed those hopes, said Gaudet, who was not involved in the research either.
Current and recent use of hormonal contraceptives was associated with a 20 percent increased risk of breast cancer. Risk increased with longer use, from a 9 percent increase in risk with less than a year of contraceptive use to a 38 percent increase after more than 10 years of use.
Researchers analyzed the health records of 1.8 million women, ages 15 to 49, in Denmark.
“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 Dr. Marisa Weiss told The New York Times. Weiss was not involved in the study.
David J. Hunter, a professor at the University of Oxford, told The New York Times there are no new contraceptives that are risk-free.
“There was a hope that the contemporary preparations would be associated with lower risk,” Hunter said. “This is the first study with substantial data to show that’s not the case.”
Results were published Wednesday in the New England Journal of Medicine. Novo Nordisk Foundation funded the research, but played no role in designing the study. The foundation has ties to the Danish pharmaceutical company Novo Nordisk, which primarily makes diabetes drugs and does not make contraceptives.
Researchers said they accounted for education, childbirth and a family history of breast cancer during the study but they were not able to adjust for several other known cancer risk factors such as alcohol use and limited physical activity, or protective factors such as breast-feeding.
Dr. Roshni Rao, a breast surgeon at New York-Presbyterian/Columbia University Medical Center, said women with a history of breast cancer may want to consider asking about other contraceptives.
"Oral contraceptives are like any other medication," Rao said. "There are risks and there are benefits. If you have a reason to be taking them, it's perfectly reasonable to do so."
About 140 million women use some type of hormonal contraception, including about 16 million in the United States.
The Associated Press contributed to this report.