EMERGING evidence supports a role for vitamin D in regulating blood glucose, particularly among individuals with Type 2 diabetes (T2D). While observational studies have previously highlighted links between vitamin D deficiency and poor glycaemic control, intervention trials have produced inconsistent results. A recent network meta-analysis offers greater clarity by directly comparing different dosing strategies of vitamin D supplementation in adults with T2D. Notably, it finds that even low-dose vitamin D may offer measurable benefits for blood glucose regulation.
The analysis included 40 randomised controlled trials published before 12 September 2024, identified through systematic searches of PubMed, EMBASE, the Cochrane Library, and Web of Science. The studies were grouped based on vitamin D dosage strategies: low (<1,000 IU/day), medium (1,000–2,000 IU/day), high (2,000–4,000 IU/day), and extremely high (≥4,000 IU/day). The researchers evaluated the effects of these regimens on key glucose-related indicators, including fasting blood glucose (FBG), HbA1c, fasting insulin (FIN), and serum 25-hydroxyvitamin D (25-[OH]-D) levels.
Results showed a dose-dependent increase in 25-(OH)-D, with the highest levels observed in the extremely high-dose group (EHDS), ranking at 91.2% probability for optimal increase. EHDS also significantly reduced FBG compared with no treatment. Low-dose supplementation (LDS) was associated with a meaningful reduction in HbA1c, while vitamin D₂ (as opposed to D₃) also improved FBG levels. Medium-dose supplementation (MDS) significantly reduced FIN both compared with placebo (mean difference: -4.76; 95% CI: -8.91–-0.61) and no treatment (mean difference: -7.30; 95% CI: -14.44–-0.17).
This network meta-analysis suggests that vitamin D supplementation could serve as an adjunct strategy for glycaemic management in adults with T2DM. While higher doses were most effective at raising 25-(OH)-D levels, modest doses yielded meaningful improvements in glycaemic indicators, particularly HbA1c and FIN. However, heterogeneity among the included studies, differences in vitamin D forms, and varying baseline vitamin D status may limit the generalisability of results. For clinical practice, these findings highlight the potential of tailoring vitamin D dosage to individual patient needs as part of a broader glycaemic control strategy.
Reference
Zhang X J et al. Effects of Oral Vitamin D Supplementation on Vitamin D Levels and Glycemic Parameters in Patients with Type 2 Diabetes Mellitus: A Systematic Review and Network Meta-Analysis. Biomed Environ Sci. 2025;38(6):716-26.
