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=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=64%).

Conclusions: Despite evidence implicating vitamin D in NAFLD pathogenesis, serum 25-hydroxyvitamin D may not be associated with NAFLD histologic severity.