Zinc supplementation in patients with cirrhosis and hepatic encephalopathy: a systematic review and meta-analysis

BACKGROUND: Low serum zinc level is associated with hepatic encephalopathy (HE), but the efficacy of zinc supplementation remains uncertain. This study aimed to investigate the effects of zinc supplementation on HE treatment in patients with cirrhosis. METHODS: We searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials (Cochrane CENTRAL) and Scopus from inception to December 2018; without publication date or language restrictions. Randomized controlled trials of zinc supplementation versus placebo or other treatment for the management of HE in adult patients with cirrhosis were selected. The primary outcome was the degree of HE as assessed by clinical signs or specialized psychometric tests. The secondary outcomes included serum ammonia levels, adverse events, or the length of hospital stay and costs. We carried out a meta-analysis with random effects model and summarized continuous outcomes using standardized mean differences (SMD) or mean differences (MD) with 95% confidence intervals (95% CI). The risk of bias was assessed using the Cochrane risk of bias tool, and the certainty of evidence for each outcome was evaluated with the Grading of Recommendations, Assessment, Development, and Evaluation approach. RESULTS: Four trials with 247 patients were included. In patients with cirrhosis who had mild HE (≤ grade II), the available evidence suggested that the combination treatment of zinc supplementation and lactulose over 3 to 6 months significantly improved performance in the number connection test (SMD: -0.97; 95% CI: − 1.75 to − 0.19; P = 0.01; moderate certainty), reported in three trials (n = 227). However, compared with lactulose therapy alone, additional zinc supplementation demonstrated no significant difference in the digit symbol test (SMD: 0.44; 95% CI: − 0.12 to 1.00; P = 0.12; very low certainty) or serum ammonia levels (MD: -10.86; 95% CI: − 25.73 to 4.01; P = 0.15; very low certainty), reported in two trials (n = 137). None of the included trials reported adverse events or effects on hospitalization. CONCLUSIONS: In conclusion, a combination of zinc supplementation and lactulose over 3 to 6 months may improve the number connection test in cirrhotic patients with low grade HE, compared with lactulose only. TRIAL REGISTRATION: PROSPERO: CRD42017080955. Registered 23 November 2017 ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12937-019-0461-3) contains supplementary material, which is available to authorized users.