Effect of Vitamin D Supplementation on Glycemia and Insulin Resistance

In a systematic review and meta-analysis, the authors searched databases including MEDLINE, EMBASE and the Cochrane Library for randomized controlled trials comparing vitamin D or analogues with placebo.

They extracted data on fasting glucose, glycemic control, insulin resistance, insulin/C-peptide levels, micro- and macrovascular outcomes and progression from non-diabetes to diabetes. Studies were assessed independently by two reviewers according to a pre-specified protocol.

Fifteen trials were included in the systematic review. The trial reporting was of moderate, variable quality. Combining all studies, no significant improvement was seen in fasting glucose, HbA1c or insulin resistance in those treated with vitamin D compared with placebo.

For patients with diabetes or impaired glucose tolerance, meta-analysis showed a small effect on fasting glucose (–0.32 mmol/l, 95% CI –0.57 to –0.07) and a small improvement in insulin resistance (standard mean difference –0.25, 95% CI –0.48 to –0.03). No effect was seen on glycated h in patients with diabetes and no differences were seen for any outcome in patients with normal fasting glucose.

Insufficient data were available to draw conclusions regarding micro- or macrovascular events; two trials failed to show a reduction in new cases of diabetes in patients treated with vitamin D.

In conclusion, they stated that, there is currently insufficient evidence of beneficial effect to recommend vitamin D supplementation as a means of improving glycemia or insulin resistance in patients with diabetes, normal fasting glucose or impaired glucose tolerance.

Diabetic Medicine, 07/25/2012