Adequate Vitamin D May Reduce Uterine Fibroid Risk

Larry Hand

April 18, 2013

Women with sufficient levels of vitamin D may be about a third less likely to develop uterine fibroids, noncancerous tumors that are the leading cause of hysterectomy, according to an article published in the May issue of Epidemiology.

Donna Day Baird, PhD, from the Epidemiology Branch of the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, and colleagues analyzed the records of1036 women of the Washington, DC, area who were screened for fibroids using ultrasound and who gave blood samples to measure their vitamin D levels. The researchers classified those with more than 20 ng/mL of the circulating form of vitamin D, 25-hydroxy D, as having sufficient levels.

The women, 620 of whom were black and 416 of whom were white, ranged in age from 35 to 49 years and were members of an urban health plan between 1996 and 1999. They also answered simple questionnaires about how many hours they spent outdoors in sunlight.

Using logistic regression analysis and controlling for factors including ethnicity, age of menarche, pregnancy history, and body mass index, the researchers found that women with sufficient vitamin D levels were 32% less likely to have fibroids than women with insufficient vitamin D (adjusted odds ratio [OR], 0.68; 95% confidence interval [CI], 0.48 - 0.96), with the association being similar among blacks and whites.

They also found that self-reported sun exposure of at least an hour a day during good weather was associated with 40% lower odds of fibroids relative to low sun exposure, (adjusted OR, 0.6; 95% CI, 0.4 - 0.9), again with no significant difference between blacks and whites.

Overall, only 26% of the women had sufficient levels of vitamin D; the mean vitamin D level was 14.6 ng/mL ± (standard error of the mean) 0.3. Levels were substantially lower in blacks than in whites (10.4 ng/mL ± 0.3 and 20.7 ng/mL ± 0.4, respectively; P < .001). Every 10 ng/mL increase was associated with an estimated 20% lower OR for fibroids.

The researchers conclude, "The consistency of findings for questionnaire and biomarker data, the similar patterns seen in blacks and whites, and the biological plausibility provide evidence for a possible causal relationship between sufficient vitamin D and reduced risk of fibroids that needs further investigation."

In a news release, Dr. Baird said, "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."

This study was supported by the National Institute of Environmental Health Sciences and the Office of Research on Minority, both of the National Institutes of Health. The authors have disclosed no relevant financial relationships.

Epidemiology. 2013;24:447-453. Abstract