Older women with insufficient levels of vitamin D gained more weight than those with sufficient levels of the vitamin, according to a new study funded by the National Institutes of Health and published online in the Journal of Women's Health. 

The study of more than 4,600 women ages 65 and older found that over nearly 5 years, those with insufficient levels of vitamin D in their blood gained about two pounds more than those with adequate levels.

"This is one of the first studies to show that women with low levels of vitamin D gain more weight, and although it was only two pounds, over time that can add up," said study author Erin LeBlanc, MD, an endocrinologist and researcher at the Kaiser Permanente Center for Health Research in Portland, OR.

"Nearly 80 percent of women in our study had insufficient levels of vitamin D. A primary source of this important vitamin is sunlight, and as modern societies move indoors, continuous vitamin D insufficiency may be contributing to chronic weight gain."

Vitamin D was in the news recently when a panel of primary care experts - the U.S. Preventive Services Task Force - said healthy postmenopausal women may need higher doses of the vitamin to prevent fractures, and that there isn't enough evidence to recommend the supplements for younger people.

Other expert groups, including the Endocrine Society, have a different take, saying many adults do need vitamin D supplements to keep their bones healthy. 

"Our study only shows an association between insufficient levels of vitamin D and weight gain, we would need to do more studies before recommending the supplements to keep people from gaining weight," LeBlanc said. "Since there are so many conflicting recommendations about taking vitamin D for any reason, it's best if patients get advice from their own healthcare provider."

She points out that this study was conducted among older women who, for the most part, were not trying to lose weight - though some of them did so as a natural result of aging.

About 60 percent of the 4,659 women in the study remained at a stable weight (within 5 percent of their starting weight) over the 4.5-year study period, 27 percent lost more than 5 percent of their body weight, and 12 percent gained more than 5 percent of their body weight.

Most women in the study (78 percent) had less than 30 nanograms per millimeter (ng/ml) of vitamin D in their blood - the level defined as sufficient by the Endocrine Society panel of experts who set clinical guidelines on vitamin D deficiency.

These women had higher baseline weight to begin with: 148.6 pounds, compared with 141.6 pounds for women whose vitamin D levels were 30 ng/ml or above. Insufficient levels had no association with weight changes in the entire group of women, or in the group that lost weight.

But in the group of 571 women who gained weight, those with insufficient vitamin D levels gained more - 18.5 pounds over 5 years - than women who had sufficient vitamin D. The latter group gained 16.4 pounds over the same period.

This study is part of a larger project called the Study of Osteoporotic Fractures that has been ongoing for more than 2 decades.

From 1986-1988, SOF enrolled nearly 10,000 women ages 65 and older and tracked their medical history through office and home visits, mailed surveys and telephone calls. The women are from Baltimore, Minneapolis, Portland, OR, and the Monongahela Valley near Pittsburgh.

The SOF study is supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Institute on Aging.