Introduction:L-carnitine is an amino acid that is synthesized from the amino acids lysine and methionine. Because it can be synthesized in the body, L-carnitine is usually not considered to be an essential nutrient. However, it could be classified as an essential nutrient for premature infants and other individuals who are not able to synthesize it in sufficient amounts. In addition to its use in clinical conditions, L-carnitine is used with exercise programs to reduce muscle soreness.
Active Forms: L-carnitine, L-acetylcarnitine (LAC), and L-propionylcarnitine (LPC).
Absorption: There are two mechanisms for L-carnitine absorption in the duodenum: active transport process and passive diffusion.
Functions in the Body: Branched Chain Amino Acid Conversion: L-carnitine also helps convert the branched chain amino acids to their keto-acid analogues. This enables the branched chain amino acids to be utilized for energy in conditions where there is a lack of carbohydrates such as fasting, starvation, or people who are on low carbohydrate diet.
Energy Production: One of L-carnitine’s primary functions is to transport long-chain fatty acids into the mitochondria where they undergo beta-oxidation in the production of energy.
Clinical Applications: Alcoholic Liver Disease: The lipid-lowering effect of L-carnitine helps prevent alcohol-induced hyperlipemia and accumulation of fat in livers.
Angina Pectoris: Studies report that both L-carnitine and L-propionylcarnitine prolong exercise time and increase exercise tolerance in patients with angina.
Cardiomyopathy: A subpopulation of patients with cardiomyopathy respond well to L-carnitine treatment.
Diabetes Mellitus: Both plasma and urine levels of L-carnitine are reported to be substantially reduced in diabetic patients and treatment with L-carnitine significantly improved insulin sensitivity in insulin-resistant patients with Type 2 diabetes.
Hyperthyroidism: Studies have been published that indicate L -carnitine antagonizes thyroid hormone in some tissues. A study by Benvenga, et al evaluated the clinical impact of these findings on hyperthyroid patients. This double-blind, placebo-controlled trial evaluated 50 hyperthyroid women for six months. The women were randomized to one of 5 groups ranging from strictly placebo to either 2 or 4 grams of carnitine per day for a period alternating with placebo use for a period. The trial concluded that the use of L-carnitine is effective in preventing and reducing the nine hyperthyroid related symptoms evaluated and has a beneficial effect on bone mineralization based on biochemical parameters evaluated.
Intermittent Claudication: L-propionylcarnitine was reported to be more effective than L-carnitine at improving walking capacity in patients with peripheral vascular disease.
Kidney Dialysis: L-carnitine losses contribute to hyperlipidemia during long-term dialysis and L-carnitine supplementation is reported to help in the management of this condition in patients undergoing regular dialysis.
Male Infertility: 47 men with low sperm counts for longer than two years were given one gram of L-carnitine 3 times daily for three months. 79 percent responded favorably with approximately a doubling of both sperm counts and sperm motility. In slightly larger studies, l-carnitine supplementation increased semen quality in men with lower baseline levels.
Toxicities and Precautions: There is no known toxicity associated with L-carnitine. However, the use of D-carnitine should be avoided. It competes with L-carnitine and can cause a depletion of L-carnitine in the heart and skeletal muscles, which can result in muscle pain, decreased exercise tolerance, and loss of muscle function.
