Vitamin D supplementation fails to prevent progression to type 2 diabetes

In patients without vitamin D deficiency, supplementation is unlikely to prevent prediabetes from progressing to type 2 diabetes, according to recent findings.

Rolf Jorde, MD, PhD, of Tromsø Endocrine Research Group at The Arctic University of Norway, and colleagues evaluated data from the Tromsø study conducted in 2007-2008 on 511 adults (mean age, 62 years; 314 men) with prediabetes to determine whether vitamin D supplementation prevents progression to type 2 diabetes. Participants were randomly assigned to vitamin D 20,000 IU/week for 5 years (n = 256) or placebo (n = 255). Oral glucose tolerance tests were performed annually.

At baseline, serum 25-hydroxyvitamin D levels were 59.9 nmol/L in the vitamin D group and 61.1 nmol/L in the placebo group, with no statistically significant difference between the groups. Through intervention, vitamin D levels increased to 122 nmol/L in the vitamin D group and remained stable in the placebo group.

The 5-year intervention was completed by 116 participants in the vitamin D group and 111 in the placebo group.

Type 2 diabetes developed in 40.2% of the vitamin D group and 43.9% of the placebo group with no significant differences between the two. Normal glycemic status was found in 55 participants in the vitamin D group and 41 in the placebo group.

“Our study does not support giving vitamin D for the prevention of [type 2 diabetes] or for improvement of insulin resistance or hyperglycemia,” the researchers wrote. “If there is a positive effect of vitamin D in this regard, the effect must be small. Very large studies with inclusion of vitamin D deficient subjects will be needed to show such a putative effect.” – by Amber Cox

The researchers report no relevant financial disclosures.

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