Insomnia and risk of nonalcoholic fatty liver disease: A systematic review and meta-analysis

AIM This sudy aims to investigate the association between insomnia or excessive daytime sleepiness (EDS) and risk of nonalcoholic fatty liver disease (NAFLD). METHODS We searched published studies indexed in MEDLINE and EMBASE database from inception to December 2015. Studies that reported odds ratios (ORs), risk ratios, hazard ratios or standardized incidence ratio with 95% confidence intervals (CI) comparing the risk of NAFLD among participants who had insomnia or EDS versus those without insomnia or EDS were included. Pooled ORs and 95% CI were calculated using a random-effect, generic inverse variance method of DerSimonian and Laird. Cochran's Q test and I2 statistic were used to determine the between-study heterogeneity. RESULTS Our search strategy yielded 2117 potentially relevant articles (781 articles from MEDLINE and 1336 articles from EMBASE). After comprehensive review, seven studies (three cross-sectional studies and four case-control studies) were found to be eligible and were included in the meta-analysis. The risk of NAFLD in participants who had insomnia was significantly higher with the pooled OR of 1.13 (95% CI, 1.00-1.27). The statistical heterogeneity was moderate with an I2 of 62%. Elevated risk of NAFLD was also observed among participants with EDS even though the 95% CI was wider and did not reach statistical significance (pooled OR 2.21; 95% CI, 0.84-5.82). The statistical heterogeneity was moderate with an I2 of 62%. CONCLUSIONS Our study demonstrated an increased risk of NAFLD among participants who had insomnia or EDS. Whether this association is causal needs further investigations.