Vitamin D deficiency increases the risk for developing diabetes. Correcting vitamin D deficiencies could have a major public health impact, but just how vitamin D reduces diabetes risk has been unclear.

In a paper published online on October 10 in Molecular Metabolism, Eric Lontchi-Yimagou, Ph.D., M.P.H., Preeti Kishore, M.B.B.S., Meredith A. Hawkins, M.D., and colleagues studied the effects of administering vitamin D versus placebo to 19 people who were vitamin D deficient as well as obese and insulin resistant. Supplemental vitamin D was associated with reduced expression of pro-inflammatory and pro-fibrotic genes in fat tissue and improved insulin sensitivity in the liver. To determine whether vitamin D’s effects are mediated through fat cells, the researchers also studied a mouse model in which the vitamin D receptor had been knocked out in fat cells. The mice displayed increased fat tissue fibrosis, inflammation, and insulin resistance in the liver. The findings indicate that vitamin D supplementation probably improves insulin resistance in the liver by directly affecting fat cells.

Dr. Lontchi-Yimagou is a clinical research scientist at the Global Diabetes Institute and an American Diabetes Association Fellow at Einstein. Dr. Kishore is an associate professor of medicine at Einstein. Dr. Hawkins is professor of medicine, director of the Global Diabetes Initiative and is the Harold and Muriel Block Chair in Medicine at Einstein. She also is an attending physician at Montefiore. The mouse studies were performed in collaboration with Evan Rosen, M.D., Ph.D., of Harvard Medical School and the Broad Institute.