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This 44-Year-Long Study Looked At The Links Between Cancer And Birth Control

A 44-year study found great news for users of the Pill.

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Good news for birth control users: A 44-year-long study found no increased lifetime cancer risk in women who used the birth control pill, compared with women who never did.

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The study, published in the American Journal of Obstetrics & Gynecology, is the longest-running study on the health effects of birth control pills.

General practitioners in the UK recruited over 46,000 women in 1968 and 1969 to take part in the study, which followed them until December 2012. At the time of recruitment, about half of the women were using combined oral contraceptives (birth control pills with estrogen and progestin), while the other half had never used them.

Women who had used birth control pills had a lower risk of several cancers, including colorectal, endometrial, and ovarian cancers.

Plus, the reduced risk of colorectal and ovarian cancer seemed to persist for many years after stopping — possibly more than 35 years, noted the study authors.

An increased risk of breast and cervical cancer was seen in current and recent birth control users, but those associations disappeared about five years after stopping the method.

The study found no evidence of an increased risk of either cancer later in life for women who had used birth control pills.

So even if you've been using birth control pills for the better part of a decade, it's encouraging to see that this 44-year study didn't find any long-term consequences associated with that.

Still a little worried about that slight increased risk while taking the pill? You probably don't need to be.

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We've already known about the slightly elevated risk of breast cancer while taking birth control pills, which previous research showed to be eliminated 10 years after stopping the method.

Dr. Mary Jane Minkin, OB-GYN and clinical professor at Yale School of Medicine, told BuzzFeed Health that this slight increased risk most likely means that some cancers could be more likely to grow and become detectable while you're taking hormonal contraception. These cancers typically take years to develop, says Minkin, but it makes sense that the presence of hormones may accelerate that process for some. That said, the fact that the increased risk goes away after you stop the method means that it probably isn't causing new cancers to form in your body, explained Minkin.

And about that cervical cancer risk, Minkin said it's important to remember that many people taking birth control pills (especially back in the '70s) were not also using condoms, which could put them at an increased risk of HPV, which can cause cervical cancer. Another theory is that the hormones in birth control pills might affect how your body responds to HPV infection. Regardless, it's reassuring to see that there was no long-term association between birth control pills and cervical cancer.

Finally, keep in mind that the risk of these cancers is already very low in young people, said Minkin. In the US, the absolute risk of developing breast cancer in the next 10 years is 0.06% for a 20-year-old and 0.4% for a 30-year-old. And cervical cancer occurs most often in women over age 30.

Of course, there are some limitations to this study. Most obviously: It started almost 50 years ago.

The birth control pills most women were using in this study were very different than the ones we use today. According to the study, their birth control pills usually contained 50 micrograms of estrogen, while most pills today contain about 20–30 micrograms.

Plus, the mean amount of time these women used birth control was 3.66 years, while most people stay on it for much longer than that these days.

The study authors also noted that they didn't recruit women with chronic diseases for this study, so it's possible they had a healthier-than-average cohort.

All that said, it's the longest-running study on the long-term effects of birth control, and that's pretty damn impressive.

Essentially, this new data confirms a lot of what we already knew about these associations, while also reassuring us that birth control doesn't contribute to an increased lifetime risk of cancer. Instead, it might actually have a long-term protective effect.

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