Fibroids develop from abnormal cell growth in the uterus (womb). The exact cause of these benign tumors is not known. However, both genetic and environmental conditions have been identified as contributing risk factors for fibroids. A number of factors may increase a woman’s likelihood of developing uterine fibroids. These include:

• Age. Although they can occur at any age after puberty, fibroids most frequently appear in women aged 30 to 40 years old. In addition, early age at menarche, especially before age 10, is considered a risk factor for the condition later in life.
  
  
• Genetics and heredity. Research indicates that many fibroids contain alterations in genes that code for uterine muscle cells. Women who have a mother or sister with fibroids appear to be at increased risk of developing them.
  
  
• Ethnicity. Fibroids tend to appear more frequently among black women than Caucasians. Also, black women tend to develop fibroids at younger ages, and also typically experience numerous and/or larger fibroids.
  
  
• Hormonal changes. Research indicates that the hormones estrogen and progesterone appear to influence the growth of uterine fibroids. When a woman with uterine fibroids experiences hormonal changes during pregnancy, the fibroids typically enlarge. However, after childbirth the fibroids tend to shrink back to the original size. In addition, when women stop menstruating (menopause), uterine fibroids usually shrink or disappear altogether. Other studies indicate that hormones that help the body maintain tissues, such as the insulin-like growth factor, may also affect fibroid growth.
  
  
• High-fat diet and alcohol consumption. Significant consumption of red meats (e.g., beef, ham) and alcoholic beverages, especially beer, is associated with an increased risk of developing fibroids in the uterus.
  
  
• Obesity. Having a body mass index (BMI) of 30 or greater appears to increase a woman’s risk of developing these benign tumors of the uterus.

In addition, researchers have identified certain factors that are associated with a decreased risk of developing uterine fibroids:

• Oral contraceptives. The use of low dose birth control pills is associated with a reduced risk of developing these benign tumors. However, the use of the pill at an early age, between 13 and 16 years, is associated with an increased risk of developing uterine fibroids.
  
  
• High-vegetable diet. Eating plenty of green vegetables (e.g., spinach, broccoli) is believed to be associated with a reduced risk of fibroid formation. However,  no study has demonstrated that a change in diet influences the incidence or symptoms of fibroids.
  
  
• Smoking. Some studies indicate that women who smoke appear to have a reduced risk of developing fibroids. However, the severe health consequences associated with smoking (e.g., lung cancer) outweigh any small benefit tobacco may provide against fibroids.