Women with adequate Vitamin D levels are 32% less likely to develop uterine fibroids, according to a new study published in Epidemiology journal this month (1).
Uterine fibroids are noncancerous growths attached to the uterus, and they normally affect women of childbearing age. Many women with fibroids experience no symptoms at all. In others, fibroids can cause symptoms such as heavy periods, pelvic pain, frequent urination, difficulty emptying the bladder and backache. As a result of these debilitating symptoms, fibroids are one the most common reasons for women to undergo hysterectomy.
Fibroids occur in around 20% of women, but those of African descent have been shown to have a higher incidence of fibroid formation (50-80%). They are a significant concern for women because of the difficult symptoms linked to their growth. In addition, fibroids are a particular concern to women of childbearing age as they can have a negative effect on fertility. They can block the fallopian tubes, affect blood flow to the uterine cavity, change the shape of the uterus and prevent sperm from travelling through the cervix.
In the recent study, led by Donna Baird of the National Institute of Environmental Health Sciences (NIEHS), researchers measured levels of Vitamin D
in 1,036 women between the ages of 35-49. Circulating levels of Vitamin D, also known as 25-hydroxy D, were measured using blood samples. Women with more than 20 nanograms per millilitre were classed as having sufficient levels of the vitamin, although many specialists believe that the minimum level for sufficiency should be higher still.
Study participants also completed a questionnaire on sun exposure. Those who spent more than one hour outside per day had a decreased risk of fibroids, with an estimated reduction of 40 percent. It is interesting to note that fibroids are more common in black women, and that black women also tend to have lower levels of Vitamin D as skin pigmentation reduces the formation of Vitamin D in the skin (2).
Scientists are often quick to point out that “correlation does not imply causation”, meaning that a correlation between two factors does not mean that one causes the other. However in this case the researchers provide evidence of a causal relationship. The researchers noted that treatment of cultures of human uterine fibroid tissue with a form of Vitamin D resulted in decreased cell proliferation accompanied by inhibition of molecular pathways for fibrosis. In other words, Vitamin D was found to play active role in slowing the growth of fibroid tissue.
The study authors conclude that the link between Vitamin D and uterine fibroids warrants further investigation, and it is hoped that these findings will encourage further research in this area. In the meantime, it would be wise for those affected by fibroids to take measures to ensure their Vitamin D levels are sufficient.
1. Baird D et al (2013) Vitamin D and the Risk of Uterine Fibroids. Epidemiology. May 2013. 24:3, 447-453.
2. Harris S (2006) Vitamin D and African Americans. Am Soc Nutr. April 2006. 136:4, 1126-1129.