Most of the over 100 million women who use hormonal contraceptives daily are prescribed them for birth control, but a new study says estrogen-containing contraceptives may also lower the risk of ovarian cancer, even years after discontinuing use.
While previous research has shown a lower risk of the cancer with birth control, most of the studies looked at older birth control "combined" formulas that had higher levels of estrogen than most formulations do today, in addition to another group of hormones called progestins. The newer combined hormonal contraceptive options usually contain lower amounts of estrogen, in combination with newer progestins.
"The reduction in risk of ovarian cancer that is seen with birth control pills has been known in gynecology for years, and this study adds hormonal IUDs to that list," Dr. Jennifer Ashton, ABC News’s Chief Medical Correspondent and a practicing OB-GYN said. "Since we do not have a screening test for ovarian cancer and since it affects 1 in 70 women, this is news that women need to know about, so they can discuss with their provider. However, it is also important to weigh risks of anything that has a benefit in medicine, and this is no different."
To test the newer forms of birth control and their potential relationship to ovarian cancer risk, researchers from Denmark and Scotland looked at the records of more than 1.8 million women who were prescribed hormonal birth control in Denmark between 15 and 49 years old, during a 20-year period from 1995 to 2014.
The results were surprising. Using combined hormonal contraception at any point, or in any form, was linked with a much lower risk of ovarian cancer.
The researchers estimated that hormonal contraception prevented 21 percent of ovarian cancers in the study population. Lower rates were seen in women who used contraception for longer periods of time. But, even women who had stopped using contraception had a lower risk than those who did not use it at all.
Overall, women in the study who had used hormonal contraceptives for any period of time showed a 34 percent lower risk of ovarian cancer. Women who had used them for more than 10 years showed a 74 percent lower risk.
"Based on our results, contemporary combined hormonal contraceptives are still associated with a reduced risk of ovarian cancer in women of reproductive age, with patterns similar to those seen with older combined oral products," the authors said in a statement.
The effects were not seen in women who only used progestin-only contraceptives, but researchers believe there wasn’t enough data in this small group of women; past research has shown similar benefits for progestin-only methods.
When compared to older studies, these results showed a slightly stronger connection. However, this could also be related to the age of the women in the study; women age 50 and above were excluded from analysis and ovarian cancer is most often diagnosed in women mid-life and older. As a result, the study cannot tell whether hormonal contraceptive usage has any association with ovarian cancer later in life. Additionally, researchers assumed that women who were prescribed hormonal birth control used it for the duration of time of their prescriptions.
Ovarian cancer is less common among women than many other cancers. About 21,000 cases were diagnosed in 2015, compared to 240,000 cases of breast cancers.
However, ovarian cancer often proves deadly -- in part because women often don't know they have it until later stages of the cancer when symptoms become more obvious. Only about 47 percent of U.S. women survive five years after a diagnosis, according to the American Cancer Society.
Currently, there isn’t a uniform approach to help prevent ovarian cancer for women at risk. Maintaining a healthy weight and avoiding hormone replacement therapy after menopause are some of the lifestyle choices that may reduce risk.
While birth control pills may be effective in this particular situation, they do come with some serious risks and side effects -- some of which include nausea, blood clots and developing other cancers.
For women with a high risk of developing ovarian cancer, doctors may recommend removing ovaries and fallopian tubes. Tubal ligations and hysterectomies, which remove the uterus and sometimes surrounding reproductive parts, may also lower risk. But these surgeries are usually not done for ovarian cancer prevention alone.
Although there isn't a specific preventative therapy recommended for helping to prevent ovarian cancer, doctors have other resources such as genetic counseling, or education, to come up with a safe and effective plan.
Dr. Jonathan Steinman is a physician specializing in radiology and contributor to the ABC News Medical Unit.