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.
At mbg, we've been asking questions about the birth control pill for years. But doctors and women have hoped that the newer generations of low-dose contraceptive pills, IUDs and implants eliminated the breast cancer risk of earlier, higher-dose formulations.
In the research published Wednesday in the New England Journal of Medicine, a team of scientists studied 1.8 million women between the ages of 15 and 49. The risk contributed by hormonal contraception, she says, is similar to the extra breast cancer risk contributed by physical inactivity, excessive weight gain in adulthood, or drinking an average of one or more alcoholic drinks per day. Dr. Marisa Weiss, an oncologist and founder of a website about breast cancer, told the New York Times that "Gynecologists just assumed that a lower dose of hormone meant a lower risk of cancer".
That number might seem small, but when you consider the many millions of women who take the pill, it becomes a lot more significant.
There are also numerous potential health benefits of hormonal contraceptives beyond preventing pregnancy, including decreasing the risk of endometrial, ovarian and colorectal cancers, as well as helping with menstrual cycle regularity, migraines and acne. That includes pills, patches, rings, implants or injections. Relative to the increased risk posed by other environmental factors, like smoking for lung cancer-that's about a 10 times greater risk-and having a human papillomavirus infection for cervical cancer-that may increase risk about 50 or 60 times-38 percent really isn't that much.
The idea that there is a link between hormonal contraceptive use and breast cancer is not new.
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"We did actually expect we would find a smaller increase in risk because today we have lower doses of estrogen in the hormone contraceptives, so it was surprising that we found this association", said Lina S. Mørch, a senior researcher at the University of Copenhagen and the paper's lead author.
While contraceptive drugs that contain oestrogen have always been suspected of increasing the likelihood of breast cancer, researchers had expected smaller doses of the hormone, often combined with the drug progestin, would be safer, said Lina Morch, an epidemiologist at Copenhagen University Hospital who led a study analysing the records of 1.8 million women in Denmark. "But the same elevated risk is there".
Despite the risk, women will continue to use the pharmaceuticals, Morch said.
Women who used an intrauterine device that releases only progestin also faced a 21 per cent increase in risk, compared with non-users, the study found. It's even lower among younger women since breast cancer in this age group is relatively rare. Over the past few decades, researchers tried to develop new hormonal formulas using less estrogen, which is known to promote breast cancer.
NEIGHMOND: Now, it's important to note in the study, women over 40 were more likely to suffer breast cancer than younger women in their 20s and 30s. "But we should make an individual assessment-doctor and a woman, together-to see what is the most appropriate thing for her to use".
MORCH: So it has to be balanced - the pros and cons of these contraceptives. Age, family history and weight gain later in life all contribute to breast cancer risk.