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What Causes Fibroids: The Known Risk Factors

 

Uterine fibroids, also known as leiomyomas, are the most common benign pelvic tumor in pre-menopausal women. According to the American Society for Reproductive Medicine, uterine fibroids will affect 8 in 10 African American women and 7 in 10 Caucasian women before menopause.

Despite the prevalence of the condition and the plethora of studies that have sought to explain it, the cause of fibroids is still not fully understood. However, evidence suggests that fibroids’ development can be attributed to a combination of genetic and hormonal traits.

Hormonal Risk Factors

The link between fibroids and hormones is well documented. Specifically, it is known that fibroids are estrogen-dependent. As a result, fibroids grow during a woman’s childbearing years, while the ovaries are naturally producing estrogen, and they typically shrink after the onset of menopause, when levels of the hormone drop. The influence of hormones on fibroid growth renders the following traits “risk factors”:

Age – The risk of fibroids increases with age, up to the point of menopause. Once menopause is reached and the body’s estrogen production naturally declines, fibroids typically shrink and – in many cases – disappear entirely.
Contraceptive use – Women who began taking oral contraceptives before the age of 16 are at a greater risk of developing fibroids. However, studies have revealed that using progestin-only injectable contraceptives is associated with a reduced risk of fibroids.

Obesity – Researchers believe that being obese increases the risk of uterine fibroid development, possibly due to the association between obesity and high circulating estrogen levels.


Genetic Risk Factors

Race – The connection between race and fibroids isn’t entirely understood, but an abundance of clinical data shows it to be a significant risk factor. Black women are nearly three times more likely to develop fibroids than white women. Furthermore, research has shown that black women tend to have larger and more symptomatic fibroids than women of other races.

Family health history – Researchers and medical practitioners have long observed a familial predisposition to fibroids. To date, various clinical studies have identified over 100 specific genes as having potential links to fibroid development. OB-GYN Dr. Donald Galen frequently observes the genetic trend in his fibroid patients: “It is common for a woman with fibroids to have a history of her mother, maternal aunt, or sister who also have fibroids, ” he says.


Other Risk Factors

Certain lifestyle and environmental traits have been thought to play a role in the development of fibroids, though clinical studies have yielded somewhat contradictory results.

Diet – Research has shown that women who eat a vegetarian diet are less likely to develop fibroids than women whose diets include meat. Some studies suggest that consuming more fruits, vegetables, and low-fat dairy products could reduce the risk of developing fibroids; however, the effectiveness of changing dietary habits in slowing the growth of existing fibroids or preventing the development of new fibroids has not been conclusively established.
While the exact cause of fibroids remains unclear, existing research points to a confluence of genetic and hormonal traits. Given the prevalence of the condition of uterine fibroids, its epidemiology will undoubtedly continue to be the subject of research. The risk factors that have been established, however, help us to understand who is susceptible to developing fibroids and what physical and lifestyle changes may prevent or minimize fibroids’ occurrence.

 

SOURCES:

  1. American Society for Reproductive Medicine, “Fibroid Tumor Video Transcript”, ReproductiveFacts.org: 2011.
  2. Retrieved July 13, 2015, from http://www.reproductivefacts.org/Fibroid_tumor_video/
  3. Stewart, E. “Uterine Fibroids”, New England Journal of Medicine. 2015; 372: 1646-55.
  4. Wise, L. et al. “Age-Specific Incidence Rates for Self-Reported Uterine Leiomyomata in the Black Women’s Health Study”, Obstetrics & Gynecology. Mar 2005; 105(3): 563–568.
  5. Levy, B., “Modern management of uterine fibroids”, Acta Obstetricia et Gynecologica. April 2008; 87: 812-823
  6. Burbank, F. Fibroids, Menstruation, Childbirth, and Evolution, pp. 89-90. Wheatmark, 2009. Tucson, AZ.

Fibroids Are Not Color Blind

Over the years, researchers have examined the epidemiological connection between a wide variety of patient characteristics and the occurrence of uterine fibroids, seeking to identify risk factors. Age, weight, diet, geographic location, lifestyle factors like cigarette smoking, medical conditions, and history of childbirth have all been studied, and many have been correlated with fibroids in one way or another. But time after time, study after study, one characteristic has stood out as a major indicator of fibroid risk: race. And the conclusion that researchers have consistently reached is this: uterine fibroids (also known as leiomyomas) disproportionately affect women of color.

Certain, specific differences have been seen in the cases of black women: research shows that, in comparison to white women, black women tend to develop a larger number of fibroids and experience more fibroid-related symptoms. A study published in 2013 by the American Society for Reproductive Medicine reported that, “African-American women had substantially more fibroids” with an average of 9.9 fibroids compared to the Caucasian subjects’ average of 4.5 fibroids. Additionally, Weiss et al. conducted a multi-ethnic, multisite, longitudinal study of 3,302 women ages 42-52 and concluded that “previously diagnosed leiomyomas were presenting symptoms more frequently in African-American woman than Caucasian women (85% vs. 63%)”.

The racial disparity in fibroid occurrence isn’t fully understood. The research that exists mostly defines the relative risk of the condition in terms of black and white. Obviously, black and white women aren’t the only ones affected by uterine fibroids. While very little data exists on the differences in susceptibility and symptoms between other ethnicities, a 2011 study conducted by the U.S. Armed Forces identified the relative risk of fibroids for multiple ethnic groups. The study looked at the population of active military women who were diagnosed with fibroids between 2001 and 2010: 11,931 cases were recorded. The researchers concluded that, relative to the white, non-Hispanic population, the risk of fibroids was slightly higher (1.1 times) for Hispanics and Asians/Pacific Islanders, and slightly lower (.9 times) for American Indians/Alaskan Natives. By comparison, African American women were 4.4 times more likely to have the same diagnosis, and women in the ethnic category of “Other” had almost double (1.9 times) the incidence of fibroids. These findings are depicted in the graph below.

Fibroids--race_MSMRgraph

As of now, there are no clear answers to explain why symptoms and presentation of uterine fibroids are different in women of color. However, the connection between fibroids and race is certainly a topic of interest to researchers, physicians and fibroid patients alike, and one that continues to be the subject of medical research.

Sources:

  1. Schwartz, S.M. “Epidemiology of uterine leiomyomata”, Clinical Obstetrics & Gynecology. June 2001; Vol.44(2):316-26
  2. Moorman, P.G. et al. “Comparison of characteristics of fibroids in African American and white women undergoing premenopausal hysterectomy”, Fertility & Sterility, March 2013; Vol.99(3)768-776>
  3. Weiss, G. et al. “Racial differences in women who have a hysterectomy for benign conditions”, Women’s Health Issues, May-June 2009; Vol.19(3):202-10
  4. Eltoukhi, H.M. et al. “The health disparities of uterine fibroid tumors for African American women: a public health issue”, American Journal of Obstetrics & Gynecology, March 2014; Vol.210(3)
  5. “Uterine Fibroids, Active Component Females, U.S. Armed Forces, 2001-2010”, Medical Surveillance Monthly Report, December 2011; Vol.18(12):10-13

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