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.
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.
To see whether the lower amounts of estrogen helped reduce or eliminate the added breast cancer risk, Morch and her colleagues tracked about 1.8 million women from 1995 through 2012.
These results sound scary at first. The women were followed for almost 11 years.
A large study in Denmark found using hormone based contraceptives for at least five years increases the risk for breast cancer by 20 percent. However, that number varied depending on how long women had used their particular method. And for those who take the drugs for five years or more, the risk will persist for as long as five years after they stop, she said.
The non-oral progestin-only levonorgestrel-releasing intrauterine system also showed an adjusted relative risk increase for breast cancer (1.21, 95% CI 1.11-1.33).
Third-generation contraceptive pills are displayed on January 2, 2013, in Lille, in northern France.
Newer formulations of birth control pills appear the carry the same risk of breast cancer as older versions.
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"Women in that age group [already] have a very low absolute risk of breast cancer", Gaudet said.
"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. Dr. Charles A. Leath, a gynecologic oncologist at the University of Alabama at Birmingham, said that while this pathway was plausible, it was far from certain. 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.
For some perspective, about 252,710 American women were diagnosed with breast cancer in 2017, according to estimates from the National Institutes of Health; 12.4 percent of women will hear the diagnosis at some point in their lives. What they should know, however, is that the longer they take them, the greater the chance they will develop breast cancer.
Shirazian notes that for women of average risk of breast cancer, the concern is not high. "We see from this data that is not the case". Unintended pregnancies cost the US government $21 billion in 2010, according to a report from the Guttmacher Institute. "As with any medical intervention, hormonal contraception is associated with specific health risks".
Other studies have shown hormonal birth control may lower the risk for ovarian and endometrial cancer.
Two types of birth control pills are sold in the US - one that combines synthetic versions of the hormones estrogen and progesterone, and the "minipill" that only delivers progestin, a synthetic formulation of progesterone. "Yes, hormonal contraception may increase your risk for breast cancer, but the absolute risk of breast cancer is small". Any woman's risk of breast cancer goes up as she gets older.
Women who stayed on hormones for 10 or more years experienced a 38 per cent increase in their relative risk of developing breast cancer, compared with nonusers.
The new study looked at all women in Denmark ages 15 to 49 who had not had cancer, clots in their veins, or treatment for infertility. Condoms and diaphragms do not deliver hormones.
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