L-carnitine (LC) and acetyl-L-carnitine (ALC) are naturally occurring compounds involved in energy metabolism, particularly in tissues with high energy demands—such as muscle and sperm cells.
A meta-analysis published in the Asia Pacific Journal of Clinical Nutrition (2007;16 Suppl:383–390) reviewed nine randomized, controlled clinical trials examining the effects of LC and ALC on male fertility. The analysis found that supplementation with either form of carnitine was associated with improved sperm motility and higher pregnancy rates.
There is also evidence suggesting a role for carnitine in erectile function. A placebo-controlled study published in Urology (2005;66(5):1080–1085) found that acetyl-L-carnitine (ALC) and propionyl-L-carnitine (PLC) enhanced the effectiveness of sildenafil in men with erectile dysfunction.
These findings suggest that carnitine may support male reproductive health and sexual function, particularly in men with underlying metabolic or vascular factors. However, the benefits appear to be adjunctive, not standalone, and further research is needed to define which men are most likely to benefit.
