Study author Dr. Erin LeBlanc, an endocrinologist at the Kaiser Permanente Center for Health Research in Portland, Ore., said the study involved more than 4,600 women age 65 over nearly five years.
The study, published in the Journal of Women's Health, found those with insufficient levels of vitamin D in their blood gained about 2 pounds more than those with adequate levels of the vitamin.
"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 2 pounds, over time that can add up," LeBlanc said in a statement. "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."
Seventy-eight percent of the women had less than 30 nanograms per millimeter 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.
In the group of 571 women who gained weight, those with insufficient vitamin D levels gained more -- 18.5 pounds over five years -- than women who had sufficient vitamin D," LeBlanc said. "The latter group gained 16.4 pounds over the same period."