Efficacy of vitamin D supplementation on glycaemic control in type 2 diabetes: An updated systematic review and meta-analysis of randomized controlled trials.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of 39 randomized controlled trials.
PubMed 39355942 · doi:10.1111/dom.15941
What was done
Authors conducted a systematic review and meta-analysis searching PubMed, EMBASE, Web of Science, and the Cochrane Library to assess the effects of vitamin D interventions on glycemic control in patients with type 2 diabetes. Outcomes analyzed included serum 25(OH)D, fasting blood glucose (FBG), HbA1c, fasting insulin, and Homeostasis Model Assessment for Insulin Resistance (HOMA-IR).
What was found
The meta-analysis included 39 randomized controlled trials with 2,982 subjects. Compared to control groups, vitamin D supplementation produced statistically significant reductions across all primary glycemic measures: - FBG: weighted mean difference (WMD) -0.49 mmol/L (95% CI: -0.69 to -0.28) - HbA1c: WMD -0.30% (95% CI: -0.43 to -0.18) - HOMA-IR: WMD -0.39 (95% CI: -0.64 to -0.14) - Fasting insulin: WMD -1.31 μIU/mL (95% CI: -2.06 to -0.56) Subgroup analyses showed effects varied by dosage, duration, baseline 25(OH)D, and BMI, with the most pronounced benefits observed with short-term, high-dose regimens in patients with baseline vitamin D deficiency, overweight status, or baseline HbA1c ≥8%.
Why it matters
This review synthesizes randomized trial evidence supporting vitamin D supplementation as an adjunctive therapy for type 2 diabetes, highlighting that clinical utility is highest in patients with existing deficiency or poor baseline glycemic control.
Limits
The abstract does not report study-level risk of bias, adverse effects, or statistical heterogeneity metrics. Absolute reductions in HbA1c were modest (0.30%), and the analysis relied on surrogate glycemic markers rather than long-term clinical or vascular outcomes.
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