Sunshine for the Outside and In

Uterine fibroids decreased with sufficient levels of vitamin D

/ Author:  / Reviewed by: Chris Galloway, M.D.

(RxWiki News) While soaking up rays in moderation can be beneficial for the skin, sunlight and the vitamin D that comes with it can also help women on the inside.

New research shows that women with sufficient vitamin D levels cut their risk of uterine fibroids, or non-cancerous tumors, by almost a third.

The reduced risk of uterine fibroids associated with vitamin D was consistent across different races and in two different measurements of vitamin D levels, according to the researchers.

"Need vitamin D? Get some sun."

Uterine fibroids are benign, non-cancerous tumors caused by the overproduction of certain cells inside a woman's uterus. Fibroids can continue to grow as long as a woman has her period. Symptoms range from heavy menstrual bleeding to pain during intercourse.

Researchers, led by Donna Baird, PhD, from the Epidemiology Branch at the National Institute of Environmental Health Sciences, investigated whether vitamin D is linked to these fibroids.

More than 1,000 women between 35 and 49 years of age who were members of an urban health plan were randomly enrolled in the study between 1996 and 1999. Less than half were white and the rest were black.

The researchers checked to see whether the participants had fibroids using an ultrasound screening. Masses that were at least half a centimeter in diameter were counted as a fibroid.

Women that were previously diagnosed with fibroids were able to report their condition without having an ultrasound.

The researchers also measured the amount of vitamin D in participants' blood plasma, specifically looking for 25-hydroxyvitamin D (25(OH)D). Participants also completed a survey on their sun exposure.

Half of whites and 10 percent of blacks had sufficient levels of vitamin D. In total, 80 percent of patients spent at least an hour outside in good weather each day.

Researchers found that women with sufficient vitamin D were 32 percent less likely to have fibroids compared to women with insufficient levels of the vitamin. These associations were similar between blacks and whites.

The odds of having fibroids were reduced when patients had an hour or more of sunlight each day. Researchers said that reductions were similar in both small and large fibroids.

"Both our direct measure of vitamin D status (circulating 25(OH)D) and time outside showed inverse associations with fibroid prevalence, and the associations in blacks and whites were similar," the researchers wrote in their report.

"If the associations of our vitamin D variables had been only with large fibroids, this would have suggested the possibility of stronger effects on tumor growth than on tumor initiation, but the inverse associations for both large and small fibroids suggest that both initiation and growth might be inhibited," they wrote.

The researchers noted that they were not sure when fibroids appeared in each of the patients, so the cause of the fibroids remains unclear.

The National Institute of Environmental Health Sciences, and National Institute of Health, with support from the Office of Research on Minority Health, funded the research.

The study was be published in the May 2013 issue of the journal Epidemiology.

Reviewed by: 
Review Date: 
April 19, 2013
Last Updated:
December 2, 2013