Carnitine: an overview of its role in preventive medicine.

Carnitine (beta-hydroxy-gamma-N-trimethylaminobutyric acid) is required for transport of long-chain fatty acids into the inner mitochondrial compartment for beta-oxidation. Widely distributed in foods from animal, but not plant, sources, carnitine is also synthesized endogenously from two essential amino acids, lysine and methionine. Human skeletal and cardiac muscles contain relatively high carnitine concentrations which they receive from the plasma, since they are incapable of carnitine biosynthesis themselves. Since the discovery of a primary genetic carnitine deficiency syndrome in 1973, carnitine has become the subject of extensive research. It is now recognized that carnitine deficiency may also occur secondary to genetic disorders of intermediary metabolism as well as to a variety of clinical disorders, including renal disease treated by hemodialysis, the renal Fanconi syndrome, cirrhosis, untreated diabetes mellitus, malnutrition, Reye's syndrome, and certain disorders of the endocrine, neuromuscular, and reproductive systems. Administration of the anticonvulsant valproic acid and total parenteral nutrition may also induce hypocarnitinemia. In many instances, the physiological implications of secondary carnitine deficiency have not been resolved. However, evidence for a specific carnitine requirement for the newborn, especially if preterm, is accumulating. Moreover, carnitine administration may have a favorable effect on some forms of hyperlipoproteinemia. Carnitine, now recognized as a conditionally essential nutrient, is a significant factor in preventive medicine.