In people with peripheral artery disease (PAD), L-carnitine and propionyl-L-carnitine can help reduce a symptom called intermittent claudication (leg pain during exercise) and improve exercise capacity.[1][2][3] However, in healthy people, supplementation with L-carnitine does not appear to improve exercise capacity or performance.[4][5] That said, L-carnitine may help reduce exercise-induced muscle soreness and muscle damage, particularly following resistance exercise.[6]
Supplementation with L-carnitine or acetyl-L-carnitine may improve sperm quality in males with infertility.[7][8] Similarly, L-carnitine may improve ovulation and rate of pregnancy in women with polycystic ovary syndrome.[9][10] However, there are very few studies examining the effect of carnitine on fertility; further high-quality randomized controlled trials are needed.
Supplementation with L-carnitine and acetyl-L-carnitine can lower liver enzymes[11][12][13] in people with nonalcoholic fatty liver disease (NAFLD). Furthermore, L-carnitine may also have minor beneficial effects on metabolic syndrome. For example, supplementation with L-carnitine can improve blood pressure,[14][15] blood glucose,[16] blood lipids (including triglycerides,[11][14][17][18] total cholesterol,[17][18][19] LDL-c,[18][19] and HDL[18]), and markers of oxidative stress and chronic inflammation.[20] Some meta-analyses have also found a small (on the order of 1 kg) beneficial effect of supplementation with L-carnitine, acetyl-L-carnitine, or propionyl-L-carnitine on weight loss.[21][22][23] However, because studies often also include weight loss drugs or lifestyle interventions (exercise and/or diet-induced weight loss),[24][21][22][23] further high-quality studies are needed to isolate the effect of carnitine supplements on weight loss and other aspects of metabolic syndrome.