What Causes Uterine Fibroids? 5 Risk Factors to Know, According to Experts
One of the first questions people ask when they're newly diagnosed with a health condition is "why?" Most of us want to know not just what is happening to us but why it's happening, or if there was anything we could have done differently—or anything we can do in the future to prevent a worsening of symptoms or a recurrence.
That instinct makes sense, but in the case of uterine fibroids, the "why" isn't a simple answer: there isn't a clear cause for why uterine fibroids form, at least not in the same way that decades of smoking can cause lung cancer, for example. Per the Cleveland Clinic, there is no known cause of uterine fibroids; it's still something of a mystery how and why the body develops them when it does.
But there are factors that can increase your chances of developing uterine fibroids. Here's what to know about the most common ones that can raise your risk.
What are uterine fibroids—and how common are they?
According to the Mayo Clinic, uterine fibroids are non-cancerous tumors, or growths, that form in the walls of the uterus; they vary in size, and can grow in a number of ways, including both into the uterine cavity and outside the uterus.
The Office on Women's Health estimates that anywhere from 20-80% of women have one or more uterine fibroids before the age of 50, making them a fairly common health condition affecting many women of childbearing age.
What causes uterine fibroids?
Again, doctors don't know for certain what causes uterine fibroids to grow. However, they do know that they're seen frequently in women who have certain factors in common.
Here are the most likely reasons why a woman develops uterine fibroids:
If you have a family history of uterine fibroids, it's more likely that you'll have them, too; for example, if your mother had or has them, this increases the chance that you will also, says G. Thomas Ruiz, MD, ob-gyn lead at MemorialCare Orange Coast Medical Center in Fountain Valley, California.
This may be because of the genetic component involved with the condition: researchers have noticed similar types of genetic abnormalities in some women with uterine fibroids. A 2012 American Journal of Human Genetics study finds related genetic aberrations among women with a predisposition for uterine fibroids, while a 2018 study in Nature Communications suggests that women who are prone to fibroids may also be prone to other types of hormonally-related tumors because of certain genetic abnormalities.
Estrogen and progesterone both play important roles in the reproductive health of women, reports the US Centers for Disease Control and Prevention. These hormones regulate the monthly cycle of menstruation and ovulation, influencing pregnancy and fertility.
However, both female sex hormones appear to promote uterine fibroid growth, per the Mayo Clinic. A 2011 review in the Journal of Reproductive Infertility describes estrogen and progesterone as "promoters of fibroid growth." The study goes on to suggest that when the levels of those two hormones are elevated, an increase in fibroid growth can often be observed.
There are several reasons why estrogen and progesterone levels may be higher at certain times in a woman's life, that same study reports, including:
- Being in your reproductive years versus going through menopause
- Taking hormone replacement therapy drugs
- Frequently having "anovulatory cycles," meaning cycles where your uterus doesn't produce an egg to be fertilized
Not that you can do much about it, but how old you are can impact your likelihood of having fibroids.
"Age matters a lot," Rose Chang-Jackson, MD, an ob-gyn at Austin Regional Clinic in Austin, Texas, tells Health. "The older you get, the longer your reproductive lifespan and the higher your chance of developing them," she says, referring to the cumulative effect of female sex hormones on fibroid growth.
African American women have a two- to three-times higher risk of fibroids compared to white women, states Dr. Chang-Jackson states, and although it's largely unclear why, that disparity is something that has been shown repeatedly to be true.
A 2014 review of studies published in the American Journal of Obstetrics and Gynecology, for example, asserts that the risk for African American women is three times higher, even after adjusting for other coexisting factors; it also reports that this group of women tends to be more symptomatic, have larger growths, and are more likely to require surgery for fibroids.
The review also points to a study linking low vitamin D levels to an increased risk for fibroids in Black women, though there could be other causes for race-based disparities.
Lastly, the number of children you've had can impact your chances of developing uterine fibroids, Dr. Chang-Jackson says: "If you've had more children, you're at less risk, but whether that's directly caused by having kids or not is the question."
Having never had a biological child, also called being a "nulliparous woman" in the medical world, is linked to an increase in uterine fibroids; a 2016 review in the International Journal of Fertility and Sterility asserts that pregnancy and lactation is associated with a reduced risk of developing fibroids because of an overall lower exposure to menstrual cycles, and that fibroids are more common in nulliparous women.
Other possible risk factors for uterine fibroids
Obesity. There's a possible association between obesity and uterine fibroids, but it's not necessarily straightforward, say the authors of a recent review and meta-analysis in the Journal of Epidemiology & Community Health. In fact, Dr. Ruiz says he doesn't know if obesity truly contributes to fibroids, but that obesity does mean "it's harder to diagnose [fibroids] because your pelvic exams aren't as clear." In other words, fibroids may go undetected for longer because of the challenges associated with pelvic exams on obese women, so the correlation may not be quite as simple as obesity causing fibroids.
Diet. Women with uterine fibroids may wonder if their diet contributed to growth or, conversely, if eating or avoiding certain foods could stop or slow the growth of existing fibroids. Similar to obesity, a poor diet has the potential to contribute to fibroid growth; a 2021 review of studies in the International Journal of Environmental Research and Public Health points to possible links between uterine fibroids and diets low in fruits and vegetables, diets high in dairy, and diets low in vitamin D, among others.
Early menstruation. Piggybacking off the influence of childbearing on the growth of fibroids, an early onset of menses has also been linked to an increased risk of fibroids; by simply having more periods in your lifetime, the Cleveland Clinic suggests, you might be more likely to develop fibroids, presumably because of the additional exposure to female sex hormones like estrogen and progesterone.
Can you reduce your risk of uterine fibroids?
Since genetics, hormones, age, race, and fertility are all factors out of your control, there isn't much you can do to prevent uterine fibroids if you're at a higher risk of developing them, says Dr. Chang-Jackson, though you may be able to slow their growth by living a healthy lifestyle.
"There's some question of whether or not people who have higher activity levels can decrease the growth of their uterine fibroids," she notes. "Some studies have shown that avoiding excess alcohol consumption, especially beer, for some reason, can help, as can eating less red meat and more greens and citrus fruits," she explains.
At the end of the day, however, Dr. Chang-Jackson warns that if you're "destined" to have fibroids, all your efforts may not have much of an effect; you can't change your genes or choose the number of your reproductive years, after all. Still, a healthy lifestyle is beneficial for a number of reasons, per the CDC, so it certainly can't hurt your chances to exercise, not smoke, sleep well, and eat a balanced diet.
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