The Association Between Vitamin D Deficiency and Insulin Resistance in Patients with Type 2 Diabetes: A Meta-Analysis

Abstract

Background: Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by insulin resistance and impaired glucose regulation. Emerging evidence suggests a potential link between vitamin D deficiency and insulin resistance, although findings remain inconsistent. Objective: This meta-analysis investigates the association between serum vitamin D levels and insulin resistance, measured primarily by HOMA-IR, among patients with T2DM or prediabetes. Methods: Studies were identified through a systematic search of electronic databases and included randomized controlled trials and observational studies. The pooled correlation coefficients, odds ratios, and mean differences were computed. Quality assessment was conducted using Cochrane RoB 2 and the Newcastle-Ottawa Scale. Results: A total of 15 studies involving over 12,000 participants were analyzed. The meta-analysis revealed a modest but significant inverse correlation between serum vitamin D and insulin resistance (r = -0.18, 95% CI: -0.29 to -0.08). Heterogeneity was moderate to high (I² = 67–97%), attributed to variability in vitamin D thresholds and population characteristics. Conclusion: Low vitamin D levels are modestly associated with increased insulin resistance in T2DM. While supplementation shows potential, particularly in combination therapies, further high-quality trials are necessary to establish causality and optimal therapeutic strategies.