Fibroid Causes

Uterine fibroids are the most common benign tumors of the female genital tract and are often found in women of reproductive age. By the age of 50, it’s estimated that 70 percent of Caucasian women and 80 percent of African American women will have fibroids.

Not all fibroids are symptomatic, but the complications they cause lead many women to seek fibroid treatment. Fibroids often cause severe menstrual cramping, unpredictable menstrual cycles, heavy bleeding, pelvic pain, weak bladder control, constipation, pain during intercourse, and issues related to infertility. For this reason, they are the leading cause of hysterectomy in the U.S., despite other effective treatment options.

Potential Causes

Uterine fibroids develop from the smooth muscle tissue of the uterus. It's not uncommon for one woman to have multiple fibroids of differing sizes, and some women are more susceptible to fibroids than others. While it’s unknown exactly what causes fibroids, it's believed that hormones and genetics play a role in their growth. 

Fibroids grow under the influence of hormones such as estrogen and progesterone, which increase during a woman’s reproductive years. These hormones are responsible for stimulating the development of the lining of the uterus each menstrual cycle in preparation for pregnancy. Evidence suggests that fibroid cells may be affected similarly.

Following menopause, when estrogen levels are low, fibroids shrink. While the underlying mechanisms for why this occurs aren’t fully understood, in simulated studies, fibroid size increased when exposed to hormone replacement therapy (specifically injectable estrogen replacement therapy and synthetic progesterones) and decreased when treated with anti-hormone therapy.

Clinical studies have revealed that hundreds of genes within fibroids are dysregulated, including those responsible for cell proliferation, which may be linked to uncontrolled cell growth. When compared to the normal myometrium, it was also discovered that fibroids contain heightened concentrations of both estrogen receptors and progesterone receptors.

Risk Factors Associated with Fibroids

There are a number of risk factors that make a woman more likely to develop fibroids, including race, genetics, age, and obesity.

Race - Evidence suggests that uterine fibroids have a disproportionate effect on African-American women. African-American women are more likely to have fibroids than other racial groups, are significantly more likely to experience severe or very severe symptoms. They also experience an earlier age of onset menstruation, another risk factor tied to uterine fibroids.

Genetics/Family History - Women who have a family history of uterine fibroids are three times more likely to develop uterine fibroids.

Diet and obesity - Women who are overweight are at greater risk for developing fibroids. Very heavy women are two to three times more likely to develop uterine fibroids. Dietary habits can also influence fibroid risk, specifically the intake of food additives and soybeans, which make a woman two and-a-half times likelier to develop fibroids.  

Age - Most of the time fibroids grow in women of childbearing age, such as their 30s and 40s. They are more common among premenopausal women, who are three to five times likelier to have it than postmenopausal women. Fibroid risk is reduced with age.

Starting period at a young age - Women who started their period at a young age are more likely to have fibroids. 

Women who’ve never had children - The risk of fibroids is higher in women who've never given birth. Additionally, some studies show that fibroid sizes regress after pregnancy. 

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