Women who weigh more than 154 pounds have three times the risk of developing fibroids than women weighing less than 110 pounds (Elsevier BV 2011). In one study, women with fibroids were significantly more likely to have a higher body mass index compared to women without uterine fibroids (He 2013). Fat tissue converts testosterone into estrogen, and obesity can lead to decreased levels of a protein called sex hormone binding globulin that binds to estrogen and progesterone, resulting in more unbound (active) hormones. These combined effects result in more estrogen and progesterone within the uterus, which may lead to fibroid development (Wise 2005; Sam 2007; Ciavattini 2013).
African-American women have an approximately 3-fold greater risk of developing fibroids than Caucasian women (Elsevier BV 2011). Although the precise reasons for this are unclear, increased levels of the aromatase enzyme in fibroid tissue itself may contribute; fibroid tissue from African-American women has been shown to contain higher aromatase levels than fibroid tissue from Caucasian and Japanese women (Ciavattini 2013; Bulun 2013; Ishikawa 2009).
Family History and Genetics
There is considerable evidence that heredity may be involved in some cases of uterine fibroids (Ligon 2001). Women who have a first-degree relative with uterine fibroids have a 2.5-fold increased chance of developing fibroids (Elsevier BV 2011). Also, identical twins are more likely to have fibroids than non-identical twins (Mayo Clinic 2014a).
Dietary Habits and Alcohol
There is some evidence suggesting a correlation between uterine fibroid development and dietary habits. Women who eat more red meat, drink more alcohol, and eat fewer vegetables and fruits have a significantly higher chance of developing fibroids (Mayo Clinic 2014a; Chiaffarino 1999; He 2013; Nagata 2001). Among African-American women, long-term alcohol consumption has been associated with an increased risk of fibroids (Wise 2004).
High Blood Pressure
A study of over 104 000 women reported that for every 10 mm Hg increase in diastolic blood pressure, the risk of fibroid development increased an average of 8-10%. It is hypothesized that this increase may be caused by the release of cytokines in the smooth muscle of the uterus (Boynton-Jarrett 2005; Elsevier BV 2011).
Other Risk Factors
Other factors associated with an increased risk of fibroid growth include first menstruation before 10 years of age, not having children, polycystic ovary syndrome, diabetes, and being over 40 years of age (Ciavattini 2013; Elsevier BV 2011; Islam 2013). Fibroids are associated with a group of conditions – diabetes, obesity, hypertension, and polycystic ovary syndrome – that are also associated with metabolic syndrome. Metabolic syndrome and the aforementioned conditions are often associated with insulin resistance and abnormal glucose metabolism. This connection is also suggested by evidence presented elsewhere in this protocol, as fibroids appear to respond to the antidiabetic, insulin-sensitizing drug metformin; are associated with excessive carbohydrate consumption; and respond to exercise. Many, but not all, researchers investigating this association have confirmed a relationship between abnormal glucose metabolism and uterine fibroids (Wise 2007; Kong 2014; Takeda 2008; Sadlonova 2008; Ekpo 2013).