Vitamin D and Improved Insulin Levels

Across all 3 studies, vitamin D supplementation showed beneficial effects on insulin levels, with moderate-sized effects observed in two studies and a small effect in one meta-analysis. The evidence includes a randomized controlled trial in 60 women with gestational diabetes mellitus (1000 IU/day for 42 days), which reported a significant reduction in serum insulin, and two meta-analyses in type 2 diabetes and MAFLD populations showing significant pooled reductions. Effects were typically observed at approximately 6 weeks of supplementation, though study durations were limited.

• Effective dose range: 1000 IU/day
• Studied populations: women with gestational diabetes mellitus, patients with type 2 diabetes, patients with metabolic-associated fatty liver disease

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). Dosing data is limited to a single trial (1000 IU/day), and median study duration was short (42 days). Vitamin D form was not reported in any study, so form-dependent effects cannot be assessed.