Effects of l-carnitine supplementation on glucolipid metabolism: a systematic review and meta-analysis

Background: l-carnitine supplementation has been utilized against glucolipid metabolism disruption. However, to the best of our knowledge, no meta-analysis process has analyzed the effects of l-carnitine supplementation on insulin resistance, fasting blood glucose, lipid metabolism, and liver enzyme levels in adults. Methods: Through the analysis and screening of 12 221 studies, 15 studies were selected from eligible trials for meta-analysis. Meta-analysis was performed in a random effect model with heterogeneity determined by I-2, and subgroup analyses were used to further identify the source of heterogeneity. Result: The results showed significant effects of l-carnitine on FBG (MD = -4.94 mg dL(-1), 95% CI: -7.07 to -2.82), insulin (MD = -0.99 mu U mL(-1), 95% CI: -1.41 to -0.56), HOMA-IR (MD = -0.58, 95% CI: -0.77 to -0.38), TG (MD = -11.22 mg dL(-1), 95% CI: -19.21 to -3.22), TC (MD = -6.45 mg dL(-1), 95% CI: -9.95 to -2.95, LDLc (MD = -8.28 mg dL(-1), 95% CI: -11.08 to -5.47), and ALT (MD = -19.71 IU L-1, 95% CI: -36.45 to -2.96). However, no significant effect of l-carnitine supplementation was observed in HDLc (MD = -0.77 mg dL(-1), 95% CI: -0.10 to -1.63) or AST (MD = -11.05 IU L-1, 95% CI: -23.08 to 0.99). The duration of carnitine supplementation was negatively associated with mean differences in FBG, as assessed by meta-regression. Conclusion: The current meta-analysis revealed that l-carnitine may have favorable effects on glucolipid profile, especially insulin, FBG, HOMA-IR, TG, TC, LDLc, and ALT levels.