Many studies show that oral contraceptives can also reduce the risk for cancer of the ovaries, uterus and possibly the colon.
Older contraceptives were known to carry a higher risk of breast cancer, but doctors had hoped that the newer lower-estrogen formulations might pose a lower risk.
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. Risk seemed to increase the longer the contraceptive was used. It amounted to one extra case of breast cancer among 7,700 women using hormone contraceptives per year. 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. The link with cancer risk exists not only for older generations of hormonal contraceptives but also for the products that many women use today, according to a paper published Wednesday in the New England Journal of Medicine. As research began to link estrogen to breast cancer, the FDA took off the market any formulations that had more than 50 micrograms of estrogen, Gaudet said.
Beyond the fact that they provide an effective means of contraception and may benefit women with menstrual cramping or abnormal menstrual bleeding, "the use of oral contraceptives is associated with substantial reductions in the risks of ovarian, endometrial, and colorectal cancers later in life". Most cases of breast cancer were seen in women using oral contraceptives in their 40s.
He also added the risks associated with hormonal contraception must be weighed against the benefits.
"If you compare this to other risks, such as obesity and being overweight, there's more of a risk with obesity than if you take a few years of oral contraceptives", Rao told Reuters Health by phone.
"However, the risk also with newer progestins was more consistent and convincing than expected, in particular the increased risk with hormone IUD (includes only progestin)". 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.
"There were hopes that the new formulations would not increase a user's risk of breast cancer as the older formulations did", said Mia Gaudet, strategic director of breast and gynecologic cancer research at the American Cancer Society, who was not involved in the research. "Taking a very low absolute risk and increasing it only slightly is still a relatively low risk". Still, the additional risk would result in a comparatively few additional cases of breast cancer, the researchers said. The findings indicate that the hormone progestin is adding to breast cancer risk; some of the contraceptive pills and numerous IUDs included only progestin, Mørch said. Don't forget there is relative risk of death in pregnancy, too.
The risk was 9 percent higher with less than one year of use and 38 percent higher with more than 10 years of use.
Most breast cancers are fueled by estrogen. A 20 per cent increase raises her risk to 1.74 per cent, or 1 in 57.
In Denmark, older women who have completed their families are most likely to use IUDs, including those containing hormones, and they are already more likely to develop breast cancer because of their age, Mørch said. But he suggested doctors take time to discuss the pros and cons of different types of contraception with their patients, and that they be frank about the potential risks, suggesting women reassess hormone use as they age.