lCarnitine

L-carnitine is a naturally occurring quaternary ammonium compound involved in energy metabolism. The body synthesizes L-carnitine from the amino acids lysine and methionine, mainly in the liver and kidneys. It is also obtained from dietary sources, especially red meat and dairy products. D-carnitine is not used by human metabolism, and supplements typically provide the L-isomer or acetyl-L-carnitine.

Role in metabolism: L-carnitine transports long-chain fatty acids into mitochondria for beta-oxidation, enabling energy production, particularly in tissues with high fatty-acid oxidation such as the heart and skeletal muscle. It also aids in the removal of excess acyl groups from mitochondria and helps maintain the acetyl-CoA/CoA ratio. Acylcarnitine esters formed with carnitine participate in various metabolic processes.

Clinical use and evidence: L-carnitine is prescribed for primary carnitine deficiency and certain secondary deficiencies (for example, in some metabolic disorders or repeated hemodialysis). In other conditions, including cardiovascular disease, peripheral vascular disease, or cognitive disorders, evidence is mixed. Some studies report modest improvements in exercise capacity or fatigue, while others show little or no benefit. Acetyl-L-carnitine has been explored for cognitive function and aging with inconsistent results. Supplements are not a proven substitute for medical therapy.

Safety and regulation: L-carnitine supplements are generally well tolerated at recommended doses. Common side effects include nausea, vomiting, abdominal cramps, diarrhea, and a fishy body odor due to trimethylamine production. Rare allergic reactions can occur. Caution is advised in kidney disease and during pregnancy; consult a healthcare professional before use, particularly at high doses or with other medications.