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New study sheds more light on cancer risk with the birth control pill

There have been questions about the risk of breast cancer and oral contraceptives for many years. Lately, I’ve seen this hyped by naturopaths, so-called functional medicine doctors, and period coaches on Instagram, many of whom are coincidentally selling a “post-birth control pill recovery” service. Frightening women away from oral contraceptives and helping them “heal” from being on the pill is blossoming from cottage industry to big business. 

But women deserve facts, not fear mongering. So let’s look at the risk of breast cancer and oral contraception (aka the birth control pill) as there is a new study that gives us more information on the subject. 

If you want the absolute short take, the risk of breast cancer with the birth control pill is lower than previously suspected (and it was always believed to be low) and drops back to baseline once the pill is stopped. The risk of breast cancer with the birth control pill is less than the risk due to pregnancy. The reduction in ovarian cancer and endometrial cancer is as great or even greater than previously thought and the benefit persists for decades after the birth control pill is stopped. 

What We Knew Before this New Study

Data linking the birth control pill with breast cancer has been conflicting, with some data showing an increased risk and other studies refuting that claim. A summary of all of the best available evidence had suggested that the risk of breast cancer on oral contraception increases anywhere from 8-24% depending on the length of use (longer duration of use equals the higher risk). Overall, this averages to a 20% risk. What that means in real numbers is 1 additional case of breast cancer for every 7,690 women using hormonal contraception. For women younger than 35 years, this is an 1 additional case of breast cancer for every 50,000 women using hormonal contraception. 

For perspective, the lifetime risk of dying in a pedestrian accident in the United states is one in 556, and yet no one is suggesting women shouldn’t go for walks.

It has always been important to put that breast cancer risk in perspective, something pill detractors conveniently omit. For example, the birth control pill also reduces the risk of two other cancers: ovarian cancer and endometrial cancer (cancer of the lining of the uterus). Endometrial cancer is often diagnosed in the early stages when it is treatable as it has a reliable warning sign—abnormal uterine bleeding. On the other hand, ovarian cancer often shows no symptoms, or the symptoms are nonspecific, so women are often wrongly dismissed. Consequently, many women have more advanced disease when they are eventually diagnosed and survival rates are lower. 

There are also other health benefits of the birth control pill, such as treating acne (read more about that here), treating painful and/or irregular menstrual periods, and of course pregnancy prevention (given maternal mortality, this can literally be lifesaving).   


The New Study

For this most recent study, researchers in the United Kingdom used the UK Biobank, which is a large cohort of people recruited to provide information about disease prevention, diagnosis, and treatment. It includes both retrospective data (information collected from people by memory) and prospective data (information collected in real-time as it happens).

The researchers looked at women born between 1939 and 1970, so they could capture long-term risks and/or benefits that might have appeared years after the birth control pill was stopped. The researchers were able to cross reference the data with cancer and death registries, and they controlled for as many variables as possible. Over 250,000 women were included. Of these, 210,443 (82%) had used or were still using the birth control pill, while 46,218 (18%) were never users. The numbers, how the data was collected, and the long-term follow-up makes this a strong study. 

The findings? The use of oral contraceptives was associated with an overall 30% reduced risk for both ovarian and endometrial cancer. This was not surprising. The longer the use, the greater the protection. For women who took birth control pills for 20 or more years there was a 40% reduced risk of ovarian cancer and a 60% reduced risk of endometrial cancer. This protection continued 30–35 years after stopping the birth control pill. The birth control pill is a clear winner cancer-wise for the ovary and endometrium.

With breast cancer, the findings showed a small bump in risk, about 10%, with current use and former use that stayed elevated until the age of 55, but then the risk dropped back to baseline. This is slightly lower than previously thought (as discussed above). The fact that the small breast cancer risk seemed age and time dependent in this new study may also explain some of the conflicting results in other studies. For example, one of the largest studies to date from Denmark followed women for an average of 10 years. That study found a slight increased risk for current and previous users, but it was unclear at the time if the risk ultimately dropped back down as women aged. This new study suggests the small bump in breast cancer risk is in fact reversible over time.

Statistics Detours to Explain a Cool Chart. If stats make you glassy-eyed, skip ahead to the next section.

This chart from the study shows results as horizontal lines, each paired with a vertical notch. If the vertical notch is to the left of 1 (meaning smaller than 1), that means a reduced risk of cancer and to the right an increased risk. I know statistics can be challenging, but this is such a visually impressive graph I just hand to include it. You can see the risk of ovarian cancer and endometrial cancer just keeps getting lower and lower as the notches march to the left with increased duration of use. Those for breast cancer hover around 1.

The short horizontal lines are called confidence intervals and they represent a range in which the researchers are fairly confident the true result lies. If the confidence interval crosses 1, that means there is likely no statistical difference between the groups. For breast cancer, while all the vertical notches hover just to the right of 1, meaning a small effect, all the confidence intervals cross 1 so there isn’t a high level of confidence that the results really show a true effect. But look at ovarian and endometrial cancer!

Why Is Getting This Data So Hard?

The birth control pill has been around for 60 years, why are we still needing studies to suss out cancer risk? 

While a lot of things are misogyny, at this point in time this isn’t. The risk of breast cancer in women under the age of forty-five is low and so the numbers of women who would need to be enrolled to create a valid study are huge. Also, they would need to be followed for decades and commit to one method of birth control. Women would also have to be randomized to birth control pills and/or a copper IUD, condoms, the diaphragm, or natural family planning to make sure any effect from the birth control pill was really from the pill and not related to factors involved in choosing that method. Also, requiring women to accept a method with a higher pregnancy rate wouldn’t be ethical or acceptable to many women. And finally, many women probably don’t want to be randomly assigned to a method of birth control. 

Putting It All Together

Fears that taking the birth control pill can increase the risk for breast cancer have prevented many women from using this form of birth control and many people (aka opportunists, grifters, scammers, and fraudsters) are exploiting this fear. To overstate the risk of breast cancer and ignore the reduction in ovarian and endometrial cancers is negligent and awful. It’s also patriarchal to provide disinformation about birth control. 

And what else temporarily increases a woman’s risk of breast cancer. Pregnancy. Yes, you read that correctly. (Click the link to read the study). The risk peaks about 5 years after the pregnancy. This temporary bump is greater than the increase with birth control pills. This suggests that hormones have an impact, whether they are made by the ovary or placenta or by semi-synthesis in a lab. (Scaring women about so-called Frankenhormones in the birth control pill is a common tactic). 

This may sound confusing, because many have heard that pregnancy, especially before the age of 35 is protective against breast cancer—and it is, but that applies to longer term risk. Pregnancy increases the short-term risk of breast cancer. Despite this, I don’t hear any period coaches or naturopaths or functional medicine doctors warning women to avoid pregnancy because of a short-term small bump in the risk of breast cancer.

Telling women they should fear a small risk of breast cancer from birth control pills and not from pregnancy means as long as a woman is in servitude to her uterus the risk is acceptable. And that’s bullshit.

The risk of breast cancer with the birth control pill is very, very small (this new study says 10%) and reversible and seems to be less the short-term risk imparted by pregnancy. The benefits with the birth control pill for reducing ovarian and endometrial cancer are significant (30%, greater with longer use) and last decades, never mind all the other benefits many women enjoy from the birth control pill. 

And if someone is selling any kind of post-birth control pill recovery program, coaching or supplements, well, you can’t take advice from them about the birth control pill, because they are financially invested in pill panics.