Additional treatment of vitamin D for improvement of insulin resistance in non-alcoholic fatty liver disease patients: a systematic review and meta-analysis

Insulin resistance provides an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Several studies already evaluate vitamin D supplementation for NAFLD patients in relation to insulin resistance. The results obtained still carry conflicting results. This study aimed to evaluate the effect of additional treatment of vitamin D for the improvement of insulin resistance in NAFLD patients. Relevant literatures were obtained from PubMed, Google Scholar, COCHRANE, and Science Direct database. The obtained studies were analyzed using fixed effect model or random effect model. Seven eligible studies with a total of 735 participants were included. Vitamin D supplementation improves insulin resistance in NAFLD patients, marked by reduced Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), with pooled mean difference − 1.06 (p = 0.0006; 95% CI − 1.66 to − 0.45). Vitamin D supplementation increase the level of vitamin D serum with pooled mean difference of 17.45 (p = 0.0002; 95% CI 8.33 to 26.56). Vitamin D supplementation decrease ALT levels, with pooled mean difference of − 4.44 (p = 0.02; 95% CI − 8.24 to − 0.65). No effect was observed for AST levels. Vitamin D supplementation provides beneficial effects on the improvement of insulin resistance in NAFLD patients. This supplementation may reduce HOMA-IR in such patients. It may serve as a potential adjunctive treatment for NAFLD patients.