“The implications of this study relate to the importance of performing a randomized placebo-controlled trial of vitamin D for the prevention of type 2 diabetes in those at high risk,” he told Medscape Medical News. “In the interim, clinicians should at least focus on maintaining vitamin D levels in high-risk individuals at or around 20 ng/mL,” he added.
June 25, 2011 (San Diego, California) — Higher levels of vitamin D in the blood appear to be associated with a reduced risk for incident diabetes among people at high risk for the disease, according to a new report.
Anastassios G. Pittas, MD, from the division of endocrinology, diabetes, and metabolism at the Tufts New England Medical Center in Boston, Massachusetts, and colleagues presented the findings here at the American Diabetes Association 71st Scientific Sessions.
According to Dr. Pittas, vitamin D might play a role in diabetes by improving insulin secretion and insulin sensitivity. “Most of the evidence focuses on a favorable effect in pancreatic beta cells,” he told Medscape Medical News.
To determine the relation between vitamin D status and risk for incident diabetes, the researchers analyzed data from the Diabetes Prevention Program (DPP), a 3-group trial comparing intensive lifestyle modification or metformin with placebo for the prevention of diabetes in patients with prediabetes.
The mean follow-up of the 2039-person cohort was 3.2 years. Plasma vitamin D levels were measured at yearly intervals, and subjects were assessed for incident diabetes. For this analysis, only participants in the intensive lifestyle and placebo groups of the DPP were considered.
Participants with vitamin D levels in the highest tertile (median concentration, 30.1 ng/mL) had a hazard ratio of 0.74 (95% confidence interval [CI], 0.59 to 0.93) for developing diabetes, compared with those with vitamin D levels in the lowest tertile (median concentration, 12.8 ng/mL).
The findings also suggest a dose-dependent effect for vitamin D levels; the hazard ratio for incident diabetes was lowest (0.46; 95% CI, 0.23 to 0.90) in the people with the highest vitamin D levels (50 ng/mL or higher), compared with those with the lowest levels (below 12 ng/mL).
In a subgroup analysis by tertiles of vitamin D, the association was similar in the placebo group (0.72; 95% CI, 0.53 to 0.96) and the lifestyle group (0.80; 95% CI, 0.54 to 1.14).
According to Dr. Pittas, “this study offers several methodological advantages over previous studies.” Vitamin D status was assessed multiple times during follow-up, not just once at baseline, which might not reflect long-term vitamin D status.
“Our study also includes a large clinically relevant population at high risk for diabetes, with a substantial proportion of nonwhite participants, which improves the external validity of the results,” he said. However, he added, “this is an observational study and therefore confounding cannot be excluded. It would be premature to recommend vitamin D specifically for prevention of diabetes.”
“This prospective study confirms that there is an association between levels of vitamin D and risk of diabetes, even when correcting for body weight, with no absolute threshold of serum 25-hydroxy vitamin D,” said independent commentator Clifford Rosen, MD, from the Jackson Laboratory in Bar Harbor, Maine. Dr. Rosen is a vitamin D researcher and member of the Institute of Medicine Committee that reviewed the evidence on calcium and vitamin D.