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

Adults aged 18–85 years; mixed sexes; health status included liver disease, hemodialysis, hypothyroidism, obesity, thyroid conditions, cystic acne, and healthy individuals; 19 controlled clinical trials (randomized or non-randomized), mostly parallel design with one cross-over; total participants 1206.

L-carnitine, orally administered, 500–4000 mg/day, 2–48 weeks.

L-carnitine supplementation significantly lowers liver enzyme levels (ALT by ~11 U/L, AST by ~9 IU/L, GGTP by ~7.9 IU/L). Higher doses (≥2000 mg/day) and longer duration (>12 weeks) show greater reductions; liver-disease patients tend to benefit more. These findings suggest L-carnitine may improve liver enzyme profiles in adults, particularly with liver disease.

Heterogeneity across trials (varying populations, dosages, and durations); many studies with unclear or high risk of bias; mix of randomized and non-randomized designs; varying control conditions; adherence and bioavailability not consistently assessed; results may not generalize to primary/secondary carnitine deficiency.