L - Carnitine : Therapeutic Applications of a Conditionally - Essential Amino Acid . by

A trimethylated amino acid roughly similar in structure to choline, carnitine is a cofactor required for transformation of free long-chain fatty acids into acylcarnitines, and for their subsequent transport into the mitochondrial matrix, where they undergo beta-oxidation for cellular energy production. Mitochondrial fatty acid oxidation is the primary fuel source in heart and skeletal muscle, pointing to the relative importance of this nutrient for proper function in these tissues. Although L-carnitine deficiency is an infrequent problem in a healthy, well-nourished population consuming adequate protein, many individuals within the population appear to be somewhere along a continuum, characterized by mild deficiency at one extreme, and tissue pathology at the other. Conditions which seem to benefit from exogenous supplementation of L-carnitine include anorexia, chronic fatigue, coronary vascular disease, diphtheria, hypoglycemia, male infertility, muscular myopathies, and Rett syndrome. In addition, preterm infants, dialysis patients, and HIV positive individuals seem to be prone to a deficiency of L-carnitine, and benefit from supplementation. Although available data on L-carnitine as an ergogenic aid is not compelling, under some experimental conditions pretreatment has favored aerobic processes and resulted in improved endurance performance. Altern Med Rev 1998;3(5):345-360. Introduction Although L-carnitine was originally discovered in 1905, its crucial role in metabolism was not elucidated until 1955, and primary L-carnitine deficiency was not described until 1972. The most significant source of L-carnitine in human nutrition is meat, although humans are also capable of synthesizing L-carnitine from dietary amino acids. It has generally been assumed that a well-balanced diet contains both a significant amount of carnitine, and all of the essential amino acids and micronutrients needed for carnitine biosynthesis; however, increasingly investigators have identified conditions and individuals for which L-carnitine appears to be a conditionally-essential nutrient. Thus, although L-carnitine deficiency is an infrequent problem in a healthy, well-nourished population consuming adequate protein, many individuals within the population appear to be somewhere along a continuum characterized by mild deficiency at one extreme and tissue pathology at the other. Gregory S. Kelly, N.D.—Associate Editor, Alternative Medicine Review; Private Practice, Greenwich, CT. Correspondence address: 56 Lafayette Place, Suite C, Greenwich, CT 06830.