But what these links signify is complicated. The research has been observational, which means it offers no definitive proof that hormonal birth control such as the pill causes cancer.
And most of the studies have been based on older formulations of the pill, which contained higher doses of estrogen and different types of progestin (synthetic progesterone) than today’s pills do.
Plus, women now have many birth control options other than the pill, such as progestin-only mini-pills, injectables and implants; hormone-based vaginal rings and patches; and intrauterine devices (IUDs), which may contain progestin or no hormones at all.
So, much of the evidence linking birth control to cancer risks is based on contraceptives that aren’t very similar to what’s on the market right now, says Lisa Iversen, a research fellow and epidemiologist with the Institute of Applied Health Sciences at the University of Aberdeen. She is one of a group of scientists attempting to address the knowledge gap.
To further confuse matters, research has also associated birth control pills with a lower risk of ovarian and endometrial cancers, and IUDs with a reduced risk of cervical cancer.
What might this all mean for you? We reviewed the research and spoke with experts to find out.
What we know about risks
A 1996 review of 54 studies, which drew together much of the research on birth control pills, concluded that oral contraceptives were indeed associated with a slightly higher risk of breast cancer.
The review, published in the Lancet, also found that the higher risk returned to normal 10 years after women no longer used hormonal birth control.
But do these results still hold true for current formulations of the pill or other, more modern contraceptives?
One significant study published in 2017 in the New England Journal of Medicine found that they do. Researchers evaluated data on about 1.8 million Danish women, and found that the use of any hormone-based contraception, including progestin-only pills and hormonal IUDs, was linked with a higher risk of breast cancer. Like the Lancet review, this study also suggested that the increased risk diminishes once a person stops using hormonal birth control.
Also like the Lancet review, the study found that the rise in breast cancer risk was quite small — just one additional cancer diagnosed for every 7,690 people using hormonal birth control a year.
When it comes to cervical cancer, studies — primarily on women taking birth control pills with estrogen and progestin — suggest that any increased risk is also modest. And as with breast cancer, the risk seems to subside once you stop using the contraceptive.
Does birth control help prevent cancer?
It’s possible, say experts, that some forms of birth control may reduce the risks of certain cancers. Here’s the rundown:
Cervical cancer. A 2017 analysis of 16 studies, published in the journal Obstetrics & Gynecology, found that using an IUD was associated with a lower rate of cervical cancer.
(Currently, cervical cancer screenings and the HPV vaccine are considered key for preventing cervical cancer.)
Ovarian cancer. A 2013 analysis of studies, published in the journal Obstetrics & Gynecology, found that one case of ovarian cancer could be prevented for every 185 women taking birth control pills for five years.
Endometrial cancer. One analysis published in the Lancet Oncology in 2015, which combined the results of 36 studies, estimated that using birth control pills for 10 years reduced the risk of developing endometrial cancer by age 75 from 2.3 percent to 1.3 percent.
Hormonal IUDs are also strongly linked with a lower risk of endometrial cancer. In fact, hormonal IUDs are sometimes used as a treatment for early-stage endometrial cancer, according to a 2019 analysis in Critical Reviews in Oncology/Hematology. (Hormonal birth control is also sometimes used to reduce menstrual pain, including pain caused by endometriosis; control irregular periods; and treat acne.)
The bottom line
The use of hormonal contraception is just one of a number of factors that can influence cancer risks. Others include family history and genetic predisposition, smoking, body weight, physical activity, alcohol consumption and diet.
And it’s important to remember that the changes in cancer risk — both higher and lower — associated with hormonal contraception are quite minimal.
They’re so small that Sarah Horvath, a practicing OB/GYN and the Darney/Landy Fellow for the American College of Obstetricians and Gynecologists, says she doesn’t routinely discuss them with women as she’s helping them decide on a birth control method.
But what if you or a family member have had breast or cervical cancer? According to the World Health Organization (WHO), people with a family history of breast cancer don’t need to avoid hormonal contraception methods. Nor do those who’ve had relatives with cervical cancer. (But if you’re concerned, viable non-hormonal birth control options, such as condoms and non-hormonal IUDs, are available.)
If you have — or have had — breast cancer, however, the WHO recommends that you avoid hormonal contraception. The hormones in these products can encourage the growth of some types of breast cancer. Hormonal contraception is an option for women with cervical cancer, which isn’t responsive to hormones the way some breast cancers are.
Ultimately, the cancer-related risks and benefits of birth control may even out, at least for most people. When researchers with the University of Aberdeen followed 46,022 women in the United Kingdom — half of whom used oral contraceptives and half of whom didn’t — for up to 44 years, they found that both groups had similar overall cancer rates by the study’s end.
“You end up with this sort of neutral balance when it comes to cancer risk,” says Iversen, the lead author of the Aberdeen study.
But keep in mind that some other risks are more significant. Hormonal contraceptives that contain estrogen and progestin increase the likelihood of blood clots, stroke and heart attack. These risks rise with age and smoking status, so smokers 35 and older shouldn’t use them.
And if you have uncontrolled high blood pressure, public health experts say the heart-related downsides of birth control pills outweigh the benefits.
Copyright 2019, Consumer Reports Inc.
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