A systematic review and meta-analysis of the use of oral zinc in the treatment of hepatic encephalopathy

Background and aim: Because low serum zinc levels precipitate hepatic encephalopathy, zinc supplementation is considered a potential therapeutic option. The aim of this study was to assess the effects of oral zinc supplementation in the treatment of hepatic encephalopathy. Methods: For this systematic review and meta-analysis, data sources included electronic databases (CENTRAL, MEDLINE, EMBASE) and manual searching. Randomized clinical trials of adult patients diagnosed with liver cirrhosis and hepatic encephalopathy were included. The types of interventions considered were any oral zinc supplementation versus no intervention, placebo, or other interventions for the management of hepatic encephalopathy. The data were analyzed by calculating the RR for each trial and expressing the uncertainty as 95% CI. Continuous data were analyzed by calculating the standard mean differences (SMD) between groups within each trial and their 95% CI. Statistical heterogeneity was defined as a P-value > 0.10 (chi(2)) or I-2 > 25%. Results: Four trials with a total of 233 patients were included. Oral zinc supplementation was associated with a significant improvement in performance on the number connection test (SMD -0.62; 95% CI -1.12 to -0.11) reported in three trials (n = 189), but not with encephalopathy recurrence reduction (RR 0.64; 95% CI 0.26 to 1.59) reported in two trials (n = 169). Other clinically significant outcomes (mortality, liver related morbidity, quality of life) were not reported. Conclusion: Oral zinc supplementation improved performance on the number connection test, but no evidence about other clinical or biochemical outcomes was available.