Women with sufficient amounts of vitamin D less likely to develop uterine fibroids

Women who had sufficient amounts of vitamin D were 32 percent less likely to develop fibroids than women with insufficient vitamin D, according to a study from researchers at the National Institutes of Health.

Fibroids, also known as uterine leiomyomata, are noncancerous tumors of the uterus. Fibroids often result in pain and bleeding in premenopausal women, and are the leading cause of hysterectomy in the United States.

The study of 1,036 women, aged 35-49, living in the Washington, D.C., area from 1996 to 1999, was led by Donna Baird, Ph.D., a researcher at the National Institute of Environmental Health Sciences (NIEHS), part of NIH. Baird and her collaborators at The George Washington University and the Medical University of South Carolina screened participants for fibroids using ultrasound. They used blood samples to measure the primary circulating form of vitamin D, known as 25-hydroxy D. Those with more than 20 nanograms per milliliter of 25-hydroxy D were categorized as sufficient, though some experts think even higher levels may be required for good health. The body can make vitamin D when the skin is exposed to the sun, or vitamin D can come from food and supplements.

Study participants also completed a questionnaire on sun exposure. Those who reported spending more than one hour outside per day also had a decreased risk of fibroids. The estimated reduction was 40 percent. Although fewer black than white participants had sufficient 25-hydroxy D levels, the estimated reduction in prevalence of fibroids was about the same for both ethnic groups.

"It would be wonderful if something as simple and inexpensive as getting some natural sunshine on their skin each day could help women reduce their chance of getting fibroids," said Baird.

Baird also noted that, though the findings are consistent with laboratory studies, more studies in women are needed. Baird is currently conducting a study in Detroit to see if the findings from the Washington, D.C., study can be replicated. Other NIEHS in-house researchers, led by Darlene Dixon, D.V.M., Ph.D., are learning more about fibroid development, by examining tissue samples from study participants who had surgery for fibroids.

"This study adds to a growing body of literature showing the benefits of vitamin D," said Linda Birnbaum, Ph.D., director of NIEHS and the National Toxicology Program.