-- Women using hormonal birth control methods -- from the pill, to the ring and implants -- appeared to have a 20 percent higher risk of breast cancer, according to a new study of 1.8 million women in Denmark.
The study, which was published in the New England Journal of Medicine, included 1.8 million women over the course of nearly 11 years. Denmark has a nationwide registry, which enabled scientists to find data on the women.
The researchers addressed potential confounding factors that, on their own, could increase breast cancer risk such as smoking, family history, prior pregnancies, body-mass index and education, as a marker for socioeconomic status.
"I was hoping that I was able to recommend one product that was risk-free but could not recommend any product as risk-free," study co-author Dr. Lina Mørch told ABC News today.
According to the study, a statistically significant increase in breast cancer risk was found in women who had used hormonal contraception for at least a year. And, the breast cancer risk seemed to increase with the duration of hormonal contraceptive use.
Mørch said that the increase in risk persisted even after stopping if hormonal contraceptives had previously been used for at least five years. But this was not the case among short-term users. Mørch described "short-term users" as less than five years.
The data in the study backed up previous research linking oral contraceptive use with increased breast cancer risk. However, the increases in breast cancer risk seen in the study were relatively small and the absolute increases in breast cancer risk remained low.
Study authors said the risk of breast cancer should be balanced against the benefits of the use of hormonal contraceptives.
In previous studies, the use of oral contraceptives has been linked to lower risks of other types of cancer. Mørch said women using or considering the use of oral contraceptives should talk with their medical providers.
Mia Gaudet, Ph.D., of the American Cancer Society, told ABC News today: “Women who are using oral contraceptives might want to speak to their doctors about use before age 35 and after age 35. Depending on their reasons for using oral contraceptives, they might want to consider other options, including non-hormonal contraceptives.”
“Beyond their role as effective contraception, oral contraceptives are used to treat a variety of abnormal menstrual syndromes and have a net cancer benefit as they reduce the risk of ovarian, endometrial, and colorectal cancers,” Gaudet said.
“It's not black and white. There are a lot of things to take into account," Mørch said.