Carnitin

Carnitin, often spelled carnitine in English, is a naturally occurring quaternary ammonium compound essential for energy metabolism. The predominant form in humans is L-carnitine. It is produced endogenously—primarily in the liver and kidneys—from the amino acids lysine and methionine—and is also obtained from the diet, especially red meat and dairy products. In the body, carnitine exists as free carnitine and as acylcarnitines, a balance that reflects metabolic state.

The primary biological role of carnitine is in the mitochondrial carnitine shuttle, which transports long-chain fatty acids into mitochondria for beta-oxidation. Fatty acyl-CoA in the cytosol is converted to fatty acylcarnitine by carnitine palmitoyltransferase I (CPT I) on the outer mitochondrial membrane; the fatty acylcarnitine is shuttled across the inner membrane and re-converted to acyl-CoA by CPT II for oxidation. This process supplies acetyl units for energy production, especially in tissues with high fatty acid oxidation like heart and skeletal muscle. Acylcarnitine balance also aids in removing excess acyl groups from mitochondria.

Clinical aspects: Carnitine deficiency can be inherited or acquired and impairs fatty acid oxidation, leading to symptoms such as weakness, hypoketotic hypoglycemia, cardiomyopathy, and muscle pain. Diagnosis commonly uses plasma acylcarnitine profiling, urine organic acids, and genetic testing. Treatment for deficiency involves carnitine supplementation under medical supervision; supplementation in healthy individuals has not proven benefits and may carry risks.

Additional notes: Carnitine is used in some metabolic disorders and in contexts such as dialysis to replenish losses. Side effects of supplementation can include gastrointestinal upset and a fishy body odor at higher doses.