Does Birth Control Increase the Risk of Breast Cancer?
As we approach 50 years since birth control was legalized in the United States we have to review the risk that birth control poses to overall health and the potential link to breast cancer.
Almost 20% of women between the ages of 15 and 44 take birth control, over 10 million people. In 2020, there were 2.3 million women diagnosed with breast cancer and 685 000 deaths globally. As of the end of 2020, there were 7.8 million women alive who were diagnosed with breast cancer in the past 5 years, making it the world's most prevalent cancer. This year, an estimated 42,170 women will die from breast cancer in the U.S.
Many studies spanning the past five decades have observed a link between certain kinds of birth control pills and breast cancer. So let's review what we know so far.
First off - Birth control has become more complex over the years. There are now several different types and several different delivery methods. The pill has two main forms - a combined pill containing estrogen and progestin, and a progestin only pill. Out of these, some are monophasic dosage, and others are in multiphasic dosage. Dosage has also ranged over the years, which created different generations of pills. Pills are now much lower than the first generation. However, despite all these perceived differences, all the pills ultimately work the same way, which is to prevent ovulation from occurring. By keeping your body in a negative feedback loop of hormonal plateau, you essentially stop cycling altogether. The pills also tend to thicken cervical mucus similar to the natural infertile phases, making fertilization impossible even if an egg were to be released.
In a typical menstrual cycle, estrogen goes through a normal peak process in the follicular phase, and then levels remain low after ovulation when progesterone takes over as the primary hormone. However, we know from many epidemiological studies that prolonged and constant exposure to estrogen or estrogenic-like compounds (xenoestrogens) may increase the risk of breast cancer. We also know exposure to high levels of estrogens may cause early onset menstruation, which is linked to higher incidence of breast cancer too. Hormone replacement therapy used to treat menopausal symptoms and osteoporosis also presents a link with an increased risk of breast cancer.
Remember that the menstrual cycle is all about balance. Ovulation is the main event of the cycle and represents the dividing line between the balance of estrogen dominance and progesterone dominance through the cycle. Menstruation represents the point where both these hormones are at their lowest, more like the reset button.
Estrogen is a growth hormone, in the menstrual cycle it represents the proliferation of your uterine lining, the maturation of the egg, and the production of cervical fluid. It's a hormone that helps your body make things. Progesterone, in contrast, puts a halt to this endless growth, and represents more of a stabilizing period where the body prepares for potential fertilization of the egg. It stabilizes and nourishes the uterine lining, it helps implantation occur, and it stops the production of cervical fluid in favor of a thick mucus plug instead.
So what happens when the balance between these hormones is off? Especially, what happens if you stop ovulating for a long time? You don't make progesterone if you don't ovulate. Therefore, the balance between the two hormones is off, and instead you have estrogen unchecked by its balance hormone progesterone. This results in cell proliferation - specifically, unchecked estrogen can promote breast cancer development mostly via activation of growth factor pathways that prompt cells to divide.
In a laboratory setting, estrogen has been shown to be involved in the development and growth of breast cancer. Exposure to estrogen changes breast cells into cancerous cells in both cell cultures and rodent models. Studies on progestins (synthetic forms of progesterone) are not as conclusive and have presented conflicting information about whether or not it promotes cancer cell proliferation.
The overall consensus is that the carcinogenic effects of estrogen are from estrogen binding to estrogen receptors and activating growth factor pathways that stimulate the breast cells to proliferate. And it is because of this cancer's strong link to estrogen that many studies have already been conducted on birth control pills and breast cancer risk.
These studies are also not conclusive.
The majority show an increased risk of breast cancer with the use of birth control pills, but several others suggest no increase. In 1996 the first large scale meta-analysis was conducted. A meta-analysis is when research from multiple studies is combined and analyzed. It involved analyzing 54 studies and 53,297 women with breast cancer and 100,239 without breast cancer. It showed that the current and recent use of birth control pills within the last decade increased the relative risk of breast cancer by up to 25%. An example of relative risk is that a 40 year old woman with no family history of breast cancer has a risk that increases from 1.5% normally to 1.9% with use of birth control pills. The risk increased the younger the pills were taken, and the duration of use did not present any effect. It also noted that when women stopped taking the pills for more than 10 years the risk returned to the baseline level. Keep in mind that many of the women in this study were those who took early formulations of birth control which contained higher doses than the ones used today.
Another meta-analysis of 34 studies from Mayo Clinic in 2006 showed that birth control pills increased the relative risk of breast cancer in pre-menopausal women by 19% and the risk is highest if the pills were used before their first full term pregnancy.
Another meta-analysis with 20 studies from 1996-2011 showed similar outcomes, with a relative risk increase of breast cancer up to 30%.
For the studies that showed no risk, there was the Women’s Contraceptive and Reproductive Experiences (CARE) study that followed 4575 women with breast cancer and 4682 women without breast cancer, and found no increase from current or past use of pills regardless of all circumstances.
There are also potential problems with all of the studies methods, as they are mostly observational studies where participants self-reported their use of birth control, so there could be differences in accuracy and completeness of information recalled by the participants. The studies also included combined pills, and so we don't have the advantage of knowing whether or not the progestin used in the pill had any impact on the study results. All of this must be taken into consideration when analyzing how serious the risk is between breast cancer risk and using different contraceptive methods.
A newer study addresses some of these issues by comparing 1,102 women between the ages of 20 and 49 diagnosed with breast cancer between 1990 and 2009 and 21,952 women without breast cancer, whose birth control pill usage histories were obtained using pharmacy records. The study showed that current or recent pill use increased the relative risk of breast cancer by 50% overall. In the general population, breast cancer risk is ~1.5% for women ages 30-40, so a 50% increase represents an absolute risk increase of 3%. The risk was highest with high or moderate doses of estrogen and certain formulations of progestins. But the study showed no risk with low estrogen doses and most of the progestins.
A few recent studies have also attempted to discern the risk between different subtypes of breast cancer with the use of birth control. These studies have shown that birth control increases a type of breast cancer called triple-negative, which is more common in younger women and is aggressive and difficult to treat.
A 2009 study showed that use of birth control pills for more than one year increased the risk of triple-negative breast cancer four-fold in women younger than 40. It also showed the risk of longer duration of use and by more recent use was significantly higher for triple-negative breast cancer. Other studies have showed similar results.
So the question is what should we do about this?
The vast majority of studies here show that recent and current use of birth control increases the relative risk of breast cancer. Even the moderate dose pill, which 78% of women in the study were taking up until 2009, was shown to increase the risk by 60%. Other birth control pills increased the risk more than 200%, and some studies report an increased risk of triple negative breast cancer, more common in younger women, those who are at the age they would be taking birth control.
These numbers are obviously very troubling. Despite this, the overall risk for women under age 50 without a family history is 1.5%, so even with an increased risk of 60%, this is still an absolute risk of 3% or less. But this number is climbing.
For some, this small increased risk may be worth it when weighed against the other potential factors of their life circumstance and the perceived benefits that birth control can provide them.
However, body literacy can give you a much better understanding of what is going on with your estrogen levels over time and how to make sure its in proper balance in the menstrual cycle. We do this by observing the color, texture, and quantity of menstrual blood, as well as bleeding patterns and cervical fluid patterns. Other symptoms of estrogen excess are probably present including along the thyroid, liver, and gut pathways.
All medication carries risks, and birth control is no exception. Each person must decide whether to proceed with a particular medication when they are fully informed of the risks and by determining their personal risk to benefit ratio.
What do you think about this information? Me, personally, if I had known this before I used birth control, I doubt I would have made the same choice.
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References:
http://www.guttmacher.org/pubs/fb_contr_use.html
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