The cause of fibroids is unknown, however a combination of hormonal, genetic, and environmental factors is associated with the chance that a woman will develop symptomatic fibroids:
- Hormones: Fibroids are associated with increased estrogen production. They are rare in women less than 20 years of age as well as in postmenopausal women. Estrogen levels vary with menstruation, with menopause, and with some medications
- Environment: Alcohol consumption and a sedentary lifestyle have been associated with fibroids. Researchers are investigating how environmental toxins affect gene activity in the uterus.
- Ethnicity: Not only are African-American women more likely to develop fibroids, their fibroids occur at a younger age, and are often larger and more numerous than in other ethnic groups. Asian women have a lower incidence of symptomatic fibroids.
- BMI: Women who are overweight or obese, based on their BMI (body-mass index), have a slightly higher risk of developing fibroids.
- Pregnancy: Women who have given birth seem to have a lower risk of developing uterine fibroids. Recent information indicates that pregnancy may protect against fibroids – one theory is that fibroids are lost during the uterine changes (involution) in the weeks following childbirth.