Nonalcoholic fatty liver disease (NAFLD) is the most common cause of liver disease worldwide. If this disease is not appropriately controlled, it can eventually cause chronic liver damage, including cirrhosis and hepatocellular carcinoma. Accordingly, the adoption of appropriate interventions to control NAFLD is important for any healthcare system. The aim of the present systematic review and meta-analysis was to clarify the effect of vitamin D supplementation on NAFLD. PubMed, Scopus, Science Direct, ISI Web of Science, and Google Scholar were systematically searched up to March 2019 to find clinical trials that examined the effects of vitamin D supplementation on liver enzyme levels in NAFLD patients. Means for liver enzymes and potential sources of heterogeneity were extracted. A subgroup analysis was performed to detect potential sources of interstudy heterogeneity. Nine trials (10 arms) comprising 467 participants were eligible for meta-analysis. The results from a pooled analysis did not reveal a significant effect of vitamin D intake on alanine aminotransferase (-2.88 U/L; 95% CI, -6.03 to 0.27; I2 = 85%), aspartate aminotransferase (-0.10 U/L; 95% CI, -1.18 to 0.97; I2 = 26%), and γ-glutamyltransferase levels (0.12 U/L; 95% CI, -5.94 to 6.18; I2 = 38%). The meta-analysis suggested a significant reduction in alkaline phosphatase (-13.79 U/L; 95% CI, -22.13 to -5.45; I2 = 72%) following vitamin D supplementation. This effect was robust in the subgroup in which > 3,000 IU/day vitamin D was administered (-19.74 U/L; 95% CI, -25.36 to -14.12; I2 = 0.0%). The present meta-analysis does not suggest the efficacy of vitamin D supplementation on NAFLD treatment.
Keywords: NAFLD; meta-analysis; nonalcoholic fatty liver disease; vitamin D.