The effect of vitamin D supplementation on glucose metabolism in type 2 diabetes mellitus: A systematic review and meta-analysis of intervention studies.

Study answer

What this study found

Vitamin D produced a modest improvement in HbA1c but did not improve fasting blood glucose overall. Pooled HbA1c fell by 0.32% versus placebo (WMD -0.32% [-0.53 to -0.10], P=0.022; I2=91.9%), while fasting blood glucose showed no overall difference (WMD -2.33 mg/dl [-6.62 to 1.95], P=0.542; I2=59.2%). Higher-dose and longer-duration subgroup results were inconsistent, and sensitivity analyses in vitamin D-deficient participants or low-risk-of-bias studies were not clearly significant. Overall, the authors conclude that evidence is not robust that vitamin D reliably improves glycemic control…

Study & population

Systematic review and meta-analysis of 29 intervention studies in adults with type 2 diabetes; 22 articles provided sufficient data for meta-analysis, with HbA1c analyzed in 19 studies and fasting blood glucose in 16 studies.

Intervention

Oral vitamin D supplementation, mainly cholecalciferol, was evaluated across intervention studies versus placebo or other controls.

Key limitation

Substantial heterogeneity was present, especially for HbA1c (I2=91.9%), and regimens varied markedly by dose, duration, and formulation.

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Original abstract