L-carnitine and acetyl-L-carnitine, also known as ALCAR, fall under the generic term carnitine. Carnitine is derived from an amino acid and is found in almost all the cells in the body. Carnitine is responsible for transporting fatty acid chains to the mitochondria, where they are oxidized to produce energy. Carnitine is also responsible for removing waste products from the mitochondria.
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Structure of Carnitines
L-carnitine's official name is L-3-hydroxy-4-trimethylammonio-butanoate, and acetyl-L-carnitine's official name is 3-acetyloxy-4-trimethylammonio-butanoate. The difference in structure between the two is that acetyl-L-carnitine has an acetyl, or CH3C=O group, attached to the oxygen atom that is attached to the carbon atom next to the nitrogen atom of the ammonio group, whereas a hydrogen atom is attached to that oxygen atom in L-carnitine.
Natural Sources of L-Carnitine
According to the Linus Pauling Institute, "meat, poultry, fish, and dairy products are the richest sources of L-carnitine, while fruits, vegetables and grains contain relatively little L-carnitine." According to the Office of Dietary Supplements of the National Institutes of Health, L-carnitine is also manufactured in the liver and kidneys.
Supplementation with L-Carnitine
According to the Office of Dietary Supplements, "Healthy children and adults do not need to consume carnitine from food or supplements," as the amount made in the body is sufficient for its needs. The Food and Nutrition Board of the National Academy of Sciences has determined that carnitine is not a necessary nutrient and has therefore not set a recommended dietary allowance for carnitine.
According to the Linus Pauling Institute, dietary supplements in the United States may contain either acetyl-L-carnitine or L-carnitine, while another form of carnitine, proprionyl-L-carnitine, is available for sale in Europe. Acetyl-L-carnitine offers a secondary benefit, namely the supply of acetyl groups, which are needed to manufacture acetylcholine, a neurotransmitter, according to the Linus Pauling Institute. Acetyl-L-carnitine is also more readily absorbed in the small intestine than is L-carntitine and also more readily crosses the blood-brain barrier, according to the Office of Dietary Supplements.
Medical Uses of L-Carnitine
Scientific evidence suggests that L-carnitine should be prescribed for those with either primary or secondary carnitine deficiency, according to the Office of Dietary Supplements. Primary carnitine deficiency is a genetic disorder, while secondary carnitine deficiency is found in people with chronic renal failure and those taking some antibiotics. Only L-carnitine is used to produce prescription carnitine pills or prescription IV-solutions of carnitine.