Effect of Vitamin D Supplementation on the Incidence of Diabetes Mellitus.
What this study found
Overall, vitamin D supplementation did not reduce incident type 2 diabetes mellitus when all populations and doses were pooled: 3,424 cases; RR 0.96 (95% CI, 0.90-1.03); P = 0.30; I2 = 3%. In post hoc subgroup analyses, moderate/high-dose vitamin D (≥1000 IU/day) was associated with lower diabetes incidence: 1,019 cases; RR 0.88 (95% CI, 0.79-0.99); P = 0.03; I2 = 0%, whereas lower-dose supplementation was not effective: RR 1.02 (95% CI, 0.94-1.10); P = 0.68; I2 = 0%. Benefit also appeared restricted to non-obese participants, with BMI <30 showing RR 0.68 (95% CI, 0.53-0.89) versus BMI ≥30…
- Study & population
- Systematic review and meta-analysis of randomized trials assessing vitamin D supplementation for prevention of type 2 diabetes mellitus.
- Intervention
- Vitamin D supplementation was evaluated across randomized trials using multiple formulations, including cholecalciferol (vitamin D3), ergocalciferol (vitamin D2), and an active analogue (eldecalcitol).
- Key limitation
- The pooled analysis showed no overall effect, and the apparent benefit came from post hoc subgroup analyses by dose, BMI, and prediabetes status.
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Open PDFOriginal abstract
CONTEXT The effect of vitamin D supplementation on the risk of type 2 diabetes mellitus (T2DM) remains controversial because most randomized controlled trials (RCTs) have been small or have reported low doses of vitamin D. OBJECTIVE To conduct a meta-analysis of RCTs testing vitamin D supplementation in the prevention of T2DM. DATA SOURCES Database search of Pubmed/MEDLINE, EMBASE and the Cochrane Library was performed by two reviewers from inception through September 15, 2019. STUDY SELECTION We included RCTs that reported the effect of vitamin D supplementation for at least 1 year on T2DM prevention. DATA EXTRACTION Two independent reviewers extracted the data. The risk ratios (RRs) and 95% confidence intervals (CIs) were reported. Primary outcome of the meta-analysis was the incidence of T2DM. DATA SYNTHESIS Nine RCTs were included (43,559 participants). The mean age (SD) was 63.5 (6.7) years. The RR for vitamin D compared with placebo was 0.96 (95% CI, 0.90-1.03); P = 0.30. In trials testing moderate to high doses of supplementation (≥1000 IU/d), all conducted among participants with prediabetes, the RR for vitamin D compared with placebo was 0.88 (95% CI, 0.79-0.99). In contrast, the trials testing lower doses, which were conducted in general population samples, showed no risk reduction (RR, 1.02 [95% CI, 0.94-1.10]); P, interaction by dose = 0.04. CONCLUSION In patients with prediabetes, vitamin D supplementation at moderate to high doses (>1000 IU/d), but not at lower doses, significantly reduced the incidence risk of T2DM, compared with placebo.