Low vitamin D levels associated with diabetes; supplementation trials needed

New studies confirm that lower levels of vitamin D are associated with a higher risk of diabetes and diabetic retinopathy. But the mechanisms by which vitamin D may affect progression, beta cell function, dysglycemia, and retinopathy are not clear. Researchers say prospective vitamin D supplementation trials are the next step, and ad hoc treatment with vitamin D is not.

“We see an inverse association with serum vitamin D levels and diabetic retinopathy in children with type 1 diabetes,” said Maria Craig, PhD, School of Women’s and Children’s Health, University of New South Wales, Sydney, Australia. “But it is unclear why, and our results do not suggest wholesale vitamin D supplementation for anyone, child or adult, with diabetes.”

Craig presented 1 of 3 studies linking lower serum levels of vitamin D with increased risk of diabetes or diabetes complications at the 71st Scientific Sessions of the American Diabetes Association, in San Diego. Her group found that children with type 1 diabetes who were deficient in vitamin D were at double the risk of developing retinopathy compared to similar children with normal serum levels of vitamin D. Vitamin D deficiency was not associated with abnormal peripheral nerve function or elevated albumin excretion rate/albumin-to-creatinine ratio. Her results echo earlier findings in adults with type 2 diabetes. Biologic models suggest that increased levels of vitamin D inhibit neovascularization and angiogenesis, which protects the retina, but there are no clinical data.

An ancillary analysis of the Diabetes Prevention Program, a 3-arm trial, found that among individuals at high risk for diabetes, higher levels of vitamin D are associated with lower risk of progression to diabetes. Using the vitamin D cut-points suggested by the 2010 Institute of Medicine Dietary Reference Intake report on calcium and vitamin D, individuals with serum vitamin D levels of 50 ng/mL or higher had roughly half the risk of developing diabetes compared to those with less than 12 ng/mL. Researchers cautioned that the role of vitamin D in reducing diabetes risk needs to be confirmed in prospective supplementation trials.

Canadian researchers found an association between higher levels of vitamin D and improved beta-cell function and lower glucose levels after 3 years of follow-up. Higher baseline vitamin D significantly reduced the odds ratio for progression to type 2 diabetes even after adjustment for baseline body mass index (BMI) and changes to BMI over the 3-year follow-up period.