What are the risk factors for developing uterine fibroids?

Uterine fibroids are the most common tumour found in female reproductive organs.

Over 50% of women between the ages of 30 and 50 have fibroids, although they cause symptoms in only about 25%.

A number of possible risk factors have been identified, but very little research exists to confirm or develop information on them.

Being African American

Uterine fibroids are particularly common in African-American women, with an estimated prevalence of 50% to 75%.

These women are also more likely to have severe pain, anaemia, and larger and more numerous fibroids than women in other population groups.

Although genetics may play a role, women of African descent who live in other countries do not appear to have as high an incidence of fibroids.

This suggests that diet or other environmental factors are at work in the development of fibroids in African-American women.

High Exposure to Estrogen

Fibroids can start to grow soon after puberty, although usually they are detected when a woman reaches young adulthood.

Women with fibroids are at risk for accelerated fibroid growth when estrogen levels are high or when lifestyle behaviours keep estrogen levels high.

Some examples of risk factors for fibroids that are also associated with high estrogen exposure include the following:

• Early onset of menstrual period (before age 12).
  
• Being overweight and sedentary.
  
• Never being pregnant. The risk for fibroids decreases with more children. (This risk factor, however, may be due to a greater risk for infertility caused by fibroids in the first place.)

Combined Oral Contraceptives.

Combined oral contraceptives contain estrogen and progesterone and the evidence on their effects on fibroids have been conflicting. Early reports suggested they might be a risk factor. Most studies conducted more recently, however, have found no association and some even suggest that the newer low-dose OC combinations may be protective.

Hormone Replacement Therapy.

Hormone replacement therapies (HRT) contain estrogen alone or estrogen plus progesterone. After menopause, fibroids usually shrink. Researchers, are investigating whether the hormones used in HRT could cause existing fibroids to persist or even grow.

In summary, if HRT has an effect on fibroid growth, it is unlikely to be severe. Any increase in fibroid growth during menopause must be evaluated surgically by a gynecologist since such growth, even if a woman is on hormone replacement therapy, may mean cancer.

Other Risk Factors

Studies report a higher incidence of fibroids in women with high blood pressure and obesity.
Both fibroids and hypertension are associated with a thicker uterus, but it is not clear if or how these conditions are related.
There is also a weak association between fibroids and diabetes.