Carnitine, in the form of L-carnitine, is a trimethylated amino acid that is essential for the transformation of fatty acids into energy for muscular activity. This transformation occurs in the mitochondria, producing coenzyme A.

A typical daily diet contains from 5 to 100 mg of carnitine. Most of the carnitine in the human body is synthesized from the essential amino acid lysine with the aid of methionine, another essential amino acid. The normal rate of carnitine synthesis in humans is approximately 1.2 micromoles per kg body weightper day.

Deficiency or depletion can occur secondary to various genetic and acquired disorders and conditions that impair the efficiency of carnitine reabsorption or increase the rate of excretion. Primary carnitine deficiency usually results from genetic disorders in carnitine transport. Such deficiency usually presents before age 5, and may be manifested by progressive cardiomyopathy, skeletal muscle weakness, and episodes of fasting hypoglycemia. Dietary deficiencies are rare, but occur most often in vegetarians, preterm infants, and during pregnancy or lactation. However, as vegetarians often have low-fat diets, they often have less risk of cardiovascular disease. Deficiencies may increase symptoms of fatigue, angina, muscle weakness, or confusion.

For supplementation, the L-carnitine form, alone or bound either to acetic or propionic acid, should be used. The D-carnitine form has produced undesirable side effects and should not be used.

The primary dietary sources of L-carnitine are red meats. Secondary sources include other animal-based food products such as fish, poultry, and milk products. Lesser sources include tempeh (fermented soybeans), wheat, and avocados.

Carnitine is a zwitterionic quaternary amine with a molecular weight of 161.2 g/mol. The chemical name is beta-hydroxy-gamma-N,N,N-trimethylaminobutyric acid. The body produces carnitine, primarily in the liver and kidneys, from lysine with the help of vitamin C, pyridoxine, niacin, iron, and methionine. It is stored primarily in the skeletal muscles and heart; it is also concentrated in sperm and in the brain.

• Carnitine is available in several commercial preparations. The L-carnitine form is most often recommended. It is available alone, or linked with acetic acid or propionic acid.
• L-carnitine (LC) is the most widely available form, is least expensive, and has been studied the most.
• L-acetylcarnitine (LAC) appears to be best for Alzheimer's disease and brain defects.
• L-propionylcarnitine (LPC) may be best for angina and other cardiac problems.

• Prevention of cardiovascular diseases: Carnitine facilitates oxidation of glucose in working hearts by relieving inhibition of pyruvate dehydrogenase by fatty acids.
• Congestive heart failure: L-propionylcarnitine (LPC) improves cardiac function.
• Early administration in patients with heart attacks has been found to reduce heart damage.
• Reduction of pain of angina; may be an effective alternative to other anti-anginal agents.
• One study has suggested that carnitine may be as beneficial as quinidine in treating cardiac arrhythmia without depressing blood pressure.
• Reduction of blood triglycerides and cholesterol levels; increase in HDL levels.
• Alcoholism: May inhibit alcohol-induced fatty liver.
• Alzheimer's disease: L-acetylcarnitine (LAC) may delay progression of the disease; also may be beneficial in treating senile depression and age-related memory defect.
• Anorexia: Supplementation may be beneficial.
• Diabetes mellitus: Supplementation with carnitine assists in glucose tolerance, stimulating immune defenses, and reducing the risk and severity of some secondary complications.
• Down's syndrome: Treatment with L-acetylcarnitine (LAC) improves visual memory and attention.
• Epilepsy (childhood): intravenous L-carnitine is indicated for valproate (VPA)-induced hepatotoxicity and overdose. Oral supplementation is suggested for VPA-associated hyperammonemia or renal-associated symptoms in infants and young children, and for individuals with epilepsy using the ketogenic diet who have hypocarnitinemia.
• Chronic fatigue syndrome: L-carnitine supplementation is beneficial in the treatment of CFS.
• Hemodialysis: Relatively low doses of L-carnitine supplementation may be beneficial for hypertriglyceridemic hemodialysis patients.
• Immune system response: Even at low concentration levels, L-carnitine has been shown to neutralize lipid-induced immunosuppression; it has also been shown to increase the proliferative response of human lymphocytes following mitogenic stimulation.
• Infertility, male: In one study, supplementation was shown to increase sperm count and motility in 80% of men with abnormal sperm mobility.
• Weight loss: In addition to aiding in weight loss, or perhaps as a consequence of weight loss, carnitine has been linked to improvement of exercise capacities and endurance.

• To improve fat metabolism and muscular performance, supplementation levels of 1,000 to 2,000 mg per day, usually divided into two doses
• For treatment of ischemic heart disease and hyperlipid states (specifically, Type IV hyperlipidemia): doses of 600 to 1,200 mg tid or 750 mg bid
• For treatment of alcoholic fatty liver: 300 mg tid
• For treatment of male infertility: 300 to 1,000 mg tid

Supplements in large quantities (approximately 5 g/day by an adult) may cause diarrhea or fish odor syndrome.

• Not recommended for individuals with active liver or kidney disease.
• Supplementation for improvement of fat metabolism and muscular performance should probably be stopped one week each month.
• Additional research into long-term safety as a supplement is needed.

In an in vitro study with human muscle tissue, the addition of L-carnitine (5 mM) to muscle cultures pretreated with AZT (0.0027 to 135 mcg/mL) preserved the integrity and volume of mitochondria (Semino-Mora et al. 1994). Coadministration of L-carnitine to AIDS patients on AZT therapy may prevent the development of myotoxicity typically associated with this drug.

In one study, isolated cardiac myocytes and rat mitochondria perfused with doxorubicin (5 mM) treatment with L-carnitine reversed the cardiotoxic affects associated with the drug without affecting therapeutic effects (Sayed-Ahmed et al. 1999). In another study with mice, carnitine significantly decreased cardiac toxicity at both acute high and chronic intermittent low doses (Alberts et al. 1978). The cardiotoxic effects of doxorubicin were not observed in children treated with a combination of doxorubicin (30 to 60 mg/kg) and carnitine (1 to 2 g) (Chavez et al. 1997).

Alberts DS, Peng YM, Moon TE, Bressler R. Carnitine prevention of adriamycin toxicity in mice. Biomed. 1978;29(8):265-268.

Brass EP, Hiatt WR. The role of carnitine and carnitine supplementation during exercise in man and in individuals with special needs. J Am Coll Nutr. 1998;17:207-215.

Chavez GA, Hernandez IM, Ollarve CF, Natera YM. Myocardial protection by L-carnitine in children treated with adriamycin. Rev Lat Cardiol. 1997;18:208-214.

De Vivo DC, Bohan TP, Coulter DL, et al. L-Carnitine supplementation in childhood epilepsy: current perspectives. Epilepsia. 1998;39:1216-1225.

Elisaf M, Bairaaktari E, Katopodis K, et al. Effect of L-Carnitine supplementation on lipid parameters in hemodialysis patients. Am J Nephrol. 1998;18:416-421.

Haas EM. Staying Healthy with Nutrition. Berkley, California: Celestial Arts Publishing; 1992:65-79.

Kelly GS. L-Carnitine: therapeutic applications of a conditionally-essential amino acid. Alt Med Rev. 1998;3:345-60.

Murray MT. Encyclopedia of Nutritional Supplements. Rocklin, Calif: Prima Publishing; 1996:283-295.

Murray MT, Pizzorno JE. Encyclopedia of Natural Medicine. 2nd ed. Rocklin, Calif: Prima Publishing; 1996:206, 216, 246-247, 424, 505-506, 584.

Newstrom H: Nutrients Catalog. Jefferson, NC: McFarland & Co., Inc.; 1993:103-105.

Plioplys AV, Plioplys S. Amantadine and L-carnitine treatment of chronic fatigue syndrome. Neuropsychobiology. 1997;35(1):16-23.

Sayed-Ahmed MM, Shaarawy S, Shouman SA, Osman AM. Reversal of doxorubicin-induced cardiac metabolic damage by L-carnitine. Pharmacol Res. 1999;39(4):289-295.

Semino-Mora MC, Leon-Monzon ME, Dalakas MC. Effect of L-carnitine on the zidovudine-induced destruction of human myotubes. Part I: L-carnitine prevents the myotoxicity of AZT in vitro. Lab Invest. 1994;71(1):102-112.

Shils ME, Olson JA, Shike M, Ross AC. Modern Nutrition in Health and Disease. 9th ed. Baltimore, Md: Williams & Wilkins; 1999: 90-92; 1377-1378.

Werbach MR. Nutritional Influences on Illness. 2nd ed. Tarzana, Calif: Third Line Press; 1993:13-22, 655-671.