Women who take oral contraceptives for 10 to 15 years cut their risk of endometrial cancer in half, says a new study published in the medical journal The Lancet Oncology.
The meta-analysis, which looked at data from 36 studies and 143,019 women in high-income countries between 1965 and 2014, concluded that overall, the longer a woman takes oral contraceptives, the lower her risk of endometrial cancer.
Endometrial or uterine cancer is the most common gynecological cancer and affects 1 in 37 women in the United States, with about 55,000 new cases being diagnosed every year, according to the American Cancer Society. The disease is rare in women younger than 35, but increases sharply with age.
According to the study, a woman can reduce her risk by 25 to 50 percent by taking hormonal birth control. If a woman has never taken oral contraceptives, her lifetime risk of developing endometrial cancer before age 75 is 2 to 3 percent. If she takes oral birth control for five years her risk drops to 1.7 percent. After 10 years of oral contraceptive use, her risk drops to 1.3 percent and after 15 years of use, her risk is only 1 percent.
Since 1965, researchers estimate that the pill has prevented 400,000 cases of endometrial cancer, and 200,000 cases in the last decade alone, among women in the 21 countries included in the study.
What's more, researchers found that oral birth control's cancer-protection properties lasted for at least 30 years after women stopped taking the pill. In addition, different levels of estrogen among birth control formulas over the decades -- oral contraceptives in the 1960s had higher levels than birth control in the 1980s did, for example -- did not affect the pill's effectiveness in preventing endometrial cancer.
The reduced risk of cancer did differ among tumor types. Medium- to long-term hormonal birth control use was more effective at preventing carcinoma tumors (the more commonly diagnosed kind that grow in the body's tissue lining) and were less effective at preventing sarcomas (which are rare, difficult to treat and grow in the body's connective tissue).
While this is clearly good news for long-term birth control users, taking the pill does carry a higher risk for a few other cancers, including an increased risk of cervical and liver cancers, as well as increased blood pressure. Smokers who take the pill also have an increased risk of cardiovascular disease, according to the Mayo Clinic.
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