Complementary nutritional supplementation in insulin resistance: The role of vitamin D, berberine and chromium

Insulin resistance is a central mechanism underlying metabolic syndrome, type 2 diabetes mellitus, obesity, and related cardiometabolic disorders. This narrative review critically evaluates the current evidence regarding vitamin D, berberine, and chromium as complementary nutritional interventions for insulin resistance. A structured literature search was conducted in PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar for English-language publications published between 2010 and March 2026, with landmark earlier studies included where appropriate. Mechanistic, preclinical, observational, and clinical evidence was synthesized narratively. The reviewed supplements influence insulin resistance through distinct mechanisms involving insulin signaling, inflammation, oxidative stress, and glucose metabolism. However, clinical findings remain heterogeneous and appear to depend on baseline nutritional status, metabolic phenotype, supplement formulation, and study design. Current evidence supports their use only as adjuncts to lifestyle modification and evidence-based therapy in selected individuals with increased metabolic risk. Future well-designed randomized controlled trials are required to define their long-term efficacy, safety, and role in personalized metabolic management.