Uterine Fibroid Risk Factors
Risk factors are patient characteristics, both modifiable (such as diet) and non-modifiable (such as race), that increase the individual's’ risk of developing uterine fibroids. Two clearly-established risk factors for uterine fibroids are age and race.¹⁻²
In several high-quality epidemiological studies, women diagnosed with fibroids were significantly older than their otherwise-similar, undiagnosed counterparts.² Relative to women in their 20’s, one study showed women in their 40's and 50's have 10-fold higher risk of developing fibroids.³⁻⁴
Black women of similar age and socioeconomic status are at 2 to 3-fold higher risk of developing fibroids than their white counterparts.²⁻³ The incidence of fibroids among Hispanic, Asian, and White women is all similar.¹ Likewise, black women are often diagnosed earlier in life; fibroids in black women are often multiple, larger, and cause more-severe symptoms compared to other ethnic groups.¹⁻⁵
Disease risk factors are less-established than age and race. However one single-center, case-control study in Japan showed women with hypertension had an almost 5-fold increased risk of uterine fibroids compared to those with normal blood pressure. Likewise, some evidence has shown diabetes may increase risk of uterine fibroids.⁶
A small body of literature suggests higher body mass index (BMI) is associated with a modest increase in risk of uterine fibroids. Likewise, there is some evidence that losing weight is associated with a decreased risk of fibroids.¹ The mechanism through which obesity may cause fibroids is debated by scientists at the highest level, though it is believed to be either hormonal or inflammatory.
Pregnancy and Hormone Levels
Estrogen and progesterone - the two hormones produced by the ovaries that stimulate development of the uterine lining during each menstrual cycle, are critical for fibroid growth. Fibroids contain more estrogen and progesterone receptors than normal uterine muscle cells do. Therefore, ovarian activity is essential for fibroid growth, and most fibroids shrink after menopause. Some studies suggested a protective effect of pregnancy on fibroid development, with high parity (3 or more deliveries) decreasing the risk of fibroids up to 5-fold. The protective effect observed in said studies was attributed to sharp fluctuation in hormone levels associated with early pregnancy and postpartum period, and the known effect of hormones on fibroids.¹
Other risk factors include genetics (including family history), lifestyle, and diet.¹
 Pavone D et al. Epidemiology and Risk Factors of Uterine Fibroids. Best Pract Res Clin Obstet Gynaecol. 2018 Jan; 46:3-11.
 Anne Zimmermann et al. Prevalence, symptoms and management of uterine fibroids: an international internet-based survey of 21,746 women. BMC Womens Health. 2012; 12: 6.
 EA Stewart et al. Epidemiology of uterine fibroids: a systematic review. BJOG 2017; 124:1501-1512
 Lurie S, Piper I, Woliovitch I, Glezerman M. Age-related prevalence of sonographicaly confirmed uterine myomas. J Obstet Gynaecol 2005;25:42–4.
 Wise LA, Palmer JR, Harlow BL, et al. Reproductive factors, hormonal contraception and risk of uterine leiomyomata in African-American women: a prospective study. Am J Epidemiol 2004;159(2):113e23.
 George A Vilos et al. The management of uterine leiomyomas. SOGC Clinical Practice Guideline. No. 318, February 2015.