And not only are there a wide variety of other factors that can influence an individual's risk of breast cancer-including certain genetic mutations and their family history-but using hormonal birth control may also be associated with a decreased risk of other kinds of cancers.
Compared to what the group of researchers found in one of their other papers-that using hormonal contraception was associated with a 300 percent increase in suicide risk-"it is a modest increase", said Dr. Øjvind Lidegaard, one of the authors of the paper and a gynecologist at the University of Copenhagen. Many women have believed that newer hormonal contraceptives are much safer than those taken by their mothers or grandmothers, which had higher doses of estrogen. What they should know, however, is that the longer they take them, the greater the chance they will develop breast cancer.
About 140 million women use some type of hormonal contraception, including about 16 million in the United States. Over the years, makers of birth control pills and hormone replacement therapy for women past menopause have reduced the amount of estrogen in their products.
Use of oral contraceptives may increase risk of breast cancer, although the overall absolute increase was relatively small, according to a study from Denmark. Women who had used hormonal birth control for less than a year had only a 9 percent increase in their relative risk, while women who had used birth control for more than 10 years had a 38 percent increase.
Experts noted that oral contraceptives have some benefits as well, and are associated with reductions in ovarian, endometrial and possibly colorectal cancers later in life.
In a commentary accompanying the new study, which was published in the New England Journal of Medicine, David J. Hunter, a professor of epidemiology and medicine at the University of Oxford, said the new study did not find that any modern contraceptives were risk-free. The researchers tracked almost 1.8 million women starting in 1995 and compared those who purchased birth control methods with women who developed breast cancer.
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.
"For many women, hormonal contraception-the pill, the patch, the ring, IUDs, and the implant-is among the most safe, effective and accessible options available", said the American College of Obstetricians and Gynecologists's vice president of practice, Dr. Chris Zahn.
A new study is showing the link between the use of birth control to increased risk of breast cancer. However, he noted that the clinical implications of this study "must be placed in the context of the low incidence rates of breast cancer among younger women", pointing out that most of the new breast cancer cases occurring in the study were among women using oral contraceptives over the age of 40. Yet the new study found increased risks that were similar in magnitude to the heightened risks reported in earlier studies based on birth control pills used in the 1980s and earlier, Hunter said.
Such alternatives include a copper IUD, condoms or, if women are done having children, tubal ligation.
A 20 per cent increase in relative risk may be small in absolute terms, but the calculation changes with age.
The research also suggests that the hormone progestin - widely used in today's birth control methods - may be raising breast cancer risk. Any woman's risk of breast cancer goes up as she gets older.
But by using computer databases from national health systems, which in Denmark are comprehensive, researchers can look at years of patient data far more cheaply, and with no risk of losing contact.
IUDs infused with hormones also appear to pose a risk, Morch said, so "so there's a lot of things to take into account when deciding what type of contraception to use".