Vitamin D and histologic severity of nonalcoholic fatty liver disease: A systematic review and meta-analysis

Background: NAFLD and vitamin D deficiency often coexist and epidemiologic evidence has shown that both of these conditions share several risk factors. Recent studies investigating the relationship between vitamin D levels and severity of NAFLD showed conflicting results. Thus we conducted a systematic review and meta-analysis to evaluate association between vitamin D and NAFLD histologic severity. Methods: A comprehensive search of the databases of the MEDLINE and EMBASE was performed from inception through November 2016. Observational studies compared serum vitamin D levels among NAFLD patients with high and low histologic severity, which was determined by NAFLD activity score (NAS) and fibrosis score. We calculated pooled mean difference (MD) of 25-hydroxyvitamin D levels with 95% confidence intervals (CI) using random-effects model. Results: Data were extracted from 6 studies involving 974 NAFLD patients. There was no difference in 25-hydroxyvitamin D levels among NAFLD patients with high NAS (score of >= 5) versus low NAS (pooled MD = -0.93, 95% CI -2.45 to 0.58, I-2 = 0%) and also high fibrosis score (score of >= 3) versus low fibrosis score (pooled MD = 0.88, 95% CI -2.65 to 4.42, I-2 = 64%). Conclusions: Despite evidence implicating vitamin D in NAFLD pathogenesis, serum 25-hydroxyvitamin D may not be associated with NAFLD histologic severity. (C) 2017 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.