ASSESSING THE CORRELATION BETWEEN VITAMIN D LEVELS AND INSULIN SENSITIVITY IN PATIENTS WITH METABOLIC SYNDROME: A SYSTEMATIC REVIEW

Abstract

Background: Vitamin D deficiency has emerged as a potential modifiable risk factor in the pathogenesis of metabolic syndrome (MetS), a multifactorial condition characterized by insulin resistance, central obesity, hypertension, and dyslipidemia. Growing evidence suggests that low serum 25-hydroxyvitamin D [25(OH)D] concentrations may adversely affect glucose metabolism and insulin action.

Objectives: This systematic review aimed to evaluate the correlation between serum 25(OH)D levels and insulin sensitivity, as measured by HOMA-IR and related indices, among adults with MetS across diverse populations.

Methods: Following PRISMA 2020 guidelines, an extensive search of PubMed, Scopus, Web of Science, and Embase databases was conducted. Observational studies assessing the association between vitamin D status and insulin resistance in adults diagnosed with MetS were included. Data were extracted on study design, sample size, vitamin D assays, and insulin sensitivity measures.

Results: Eighteen studies met inclusion criteria, encompassing over 22,000 participants across North America, Asia, Europe, the Middle East, and Oceania. Serum 25(OH)D concentrations ranged from 15.8 to 67.1 nmol/L, with deficiency prevalence between 55% and 87%. Across studies, lower vitamin D levels consistently correlated with higher fasting insulin, glucose, and HOMA-IR values. Prospective evidence indicated that baseline vitamin D insufficiency predicted future declines in insulin sensitivity and increased MetS risk.

Conclusions: Findings demonstrate a consistent inverse relationship between serum vitamin D levels and insulin resistance in MetS populations, suggesting vitamin D deficiency as a plausible metabolic risk factor.