Does L-carnitine supplementation affect serum levels of enzymes mainly produced by liver? A systematic review and meta-analysis of randomized controlled clinical trials

Background and aims: l-carnitine supplementation is proposed to reduce liver enzymes levels; however, previous findings were equivocal. The current systematic review and meta-analysis of randomized controlled clinical trials (RCTs) were performed to assess the effect of l-carnitine supplementation on serum levels of enzymes mainly produced by liver [alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transpeptidase (GGTP)]. Methods: Online databases as well as the reference lists of relevant studies were searched from inception up to June 2019. The risk of bias in individual studies was assessed using Cochrane Collaboration’s tool. Data were pooled using the random-effects model and expressed as mean differences (MDs) with 95% confidence intervals (CIs). Results: In total, 18 RCTs (1161 participants) met the eligibility criteria. l-carnitine supplementation dose ranged from 500 to 4000 mg/day. l-carnitine supplementation significantly reduced serum ALT (MD = − 8.65 IU/L, 95% CI − 13.40, − 3.90), AST (MD = − 8.52 IU/L, 95% CI − 12.16, − 4.89), and GGTP (MD = − 8.80 IU/L, 95% CI − 13.67, − 3.92) levels. The subgroup analysis showed that l-carnitine might be more effective in reducing the enzymes when supplemented in higher doses (≥ 2000 mg/day), for longer durations (> 12 weeks), and among patients with liver diseases. The meta-evidence was graded as “moderate” for ALT and AST, and “low” for GGTP according to NutriGrade scoring system. Conclusion: l-carnitine supplementation significantly improves circulating ALT, AST and GGTP levels; therefore, it might positively affect liver function, especially among patients with liver diseases. Further high-quality RCTs are recommended to confirm our results.