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. Another way of looking at that is that there would be one additional case of breast cancer each year among 7,700 people who use hormonal contraceptives.
"It's really quite small - not to say it's zero".
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.
This study was done in Denmark, where every resident is on a register of medical visits and drug purchases.
Researchers analyzed health records of 1.8 million women, ages 15 to 49, in Denmark where a national health care system allows linking up large databases of prescription histories, cancer diagnoses and other information.
Women who now use or recently used hormone-based contraception face a 20 percent higher risk of breast cancer, although the overall risk for most women is relatively low, a new study of 1.8 million women in Denmark has concluded.
Breast cancer is the second-biggest cancer killer of American women, after lung cancer.
Breast cancer strikes about 255,000 US women each year and kills about 41,000, according to the American Cancer Society.
Other studies had shown about the same breast cancer risk for older versions of birth control pills.
Mørch said that "knowledge is needed on the potential beneficial influence of newer contraceptives on the risk of ovarian and colorectal cancer, since evidence now relates to older types of hormonal contraceptives".
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"Unfortunately this was not the case and additional research is needed to tweak the formulation".
Women should discuss their contraceptive options with their doctor or gynecologist, Gaudet and Morch said.
Some intrauterine devices (IUDs) do not employ hormones.
"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. "But in the study it does appear that any form is basically the same", added Dr. Taraneh Shirazian of New York University's Langone Joan H. Tisch Center for Women's Health.
The study shows that "the search for an oral contraceptive that does not elevate the risk of breast cancer needs to continue", said Dr. David Hunter of the University of Oxford in a Journal editorial. 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. 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.
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. "Taking a very low absolute risk and increasing it only slightly is still a relatively low risk". A 20 per cent increase raises her risk to 1.74 per cent, or 1 in 57.
"That is a very small extra risk. The risk of dying when you're pregnant is probably higher".
However, the overall absolute increase for breast cancer cases was relatively small, marked by an increased of around one new breast cancer case per 7,690 current and recent users of hormonal contraception (13 per 100,000 person-years, 95% CI 10-16).
Duration of use also contributed to associated breast cancer risk.
"And there is also the reassuring thought that oral contraceptive use may decrease the risk of ovarian and endometrial cancer".