This amino acid was discovered by the Russian scientist W. Gulewitsch in 1905 as a nitrogenous substance. Its structure was established by two Japanese chemists M. Tomita and Y. Sendju in 1927.

Chemical structure of L-Carnitine


Chemical and physical properties

IUPAC Name: (3R)-3-hydroxy-4-(trimethylazaniumyl)butanoate
Molecular Weight (Molar Mass): 161.1989 g/mol
Molecular Formula (Structural Formula): C7H15NO3
SMILES: [O-]C(C[C@@H](O)C[N+](C)(C)C)=O
CAS Number: 541-15-1
MDL Number: MFCD00038747
Melting point: 197-212 °C
Solubility in water: 2500 g/L (20 °C)
2D Molfile: Get the molfile

Functions of L-Carnitine in the body

A variety of therapeutic roles have been attributed to this amino acid, which undergoes rapid conversion from both lysine and methionine. The process of conversion is dependent upon adequate vitamin C being present. The supply of carnitine is especially enhanced by lysine ingestion, as compared with other amino acid precursors of carnitine such as threonine and tryptophan.

It is suggested, based on recent studies, that men have a higher need for carnitine than women. Higher levels are found in blood in men than women, and men have high levels present in the epididymis of the testes. Lysine depletion in animals results in infertility as a result of the loss of sperm motility.

Some researchers suggest that although this amino acids is not a vitamin it may be an essential nutrient in newborn infants, due to inadequate ability to synthesize it; and in adults with genetic limitations in their ability to convert methionine or lysine to carnitine.

L-Carnitine has been shown to have a profound involvement in the metabolism of fat, and in the reduction of triglycerides. Oxidation of triglycerides occurs when 1 g to 3 g of carnitine are administered daily. This is of potential value in conditions as diverse as intermittent claudication; poor hand and foot circulation; myocardial infarction and kidney disease. It transfers fatty acids across the membranes of the mitochondria (energy producing centres in all body cells), where they can be utilized as sources of energy.

A variety of other conditions have been suggested as being potential beneficiaries of carnitine supplementation, including muscular dystrophy, myotonic dystrophy, and limbgirdle muscular dystrophy, since these lead to carnitine loss in the urine and therefore greater requirements.The application to the stimulation of fat metabolism leads to possible benefits in cases of obesity. Since fat is more readily mobilized, and clearance is more rapid, with the use of carnitine, there is every reason to expect that a clinical application in this direction will be forthcoming with further research.

Carnitine has been shown to be useful in conditions of ketosis (build up of acid wastes in the blood) in individuals on diets which produce the accumulation of ketone bodies, or fat waste products, in the blood. Such a build up can acidify the blood, resulting in calcium, magnesium and potassium loss, and can indeed be life-threatening. Fat metabolism requires carnitine to be adequately present. In scurvy the fat levels of the blood are high, and this is thought to be as a result of the relationship which exists between vitamin C and carnitine. A low level of vitamin C will result in apparent carnitine deficiency.

Dietary sources

Carnitine is synthesized in the liver by humans as well as being a part of the diet in the form of muscle and organ meats. It is not found in vegetable forms of protein. This amino acid is not essential

Carnitine is predominantly found in animal products, particularly in red meat. Poultry, fish, and dairy products also contribute to carnitine intake, whereas vegetables, fruits, and grains contain minimal amounts. The bioavailability of dietary carnitine ranges from approximately 63% to 75%, although the bioavailability of acetyl-L-carnitine has not been extensively researched.

Specific information on the carnitine content of various foods is limited. The U.S. Department of Agriculture’s (USDA’s) FoodData Centralexternal link disclaimer does not include the carnitine content of foods.

Below is a list of several foods along with their approximate carnitine content per serving, based on several small studies.

A 3-ounce serving of cooked beef steak - 42–122 mg.
Cooked ground beef, in a 3-ounce serving - 65–74 mg.
One cup of whole milk - 8 mg.
In a 3-ounce serving of cooked codfish - 3–5 mg.
Cooked chicken breast, in a 3-ounce serving - 2–4 mg.
Enjoying ½ cup of ice cream - 3 mg.
Cheddar cheese, in a 2-ounce serving - 2 mg.
Two slices of whole-wheat bread - 0.2 mg.
For a ½ cup of cooked asparagus - 0.1 mg.

Dietary supplements

This amino acids is available in dietary supplements containing only carnitine or a combination of carnitine and other ingredients. The two main forms of carnitine in dietary supplements are L-carnitine and acetyl-L-carnitine, and amounts range from about 3 mg to 5,000 mg. Absorption of supplemental L-carnitine is about 14% to 18%, much less than that of dietary L-carnitine.

Dietary supplements containing carnitine are available in two main forms: L-carnitine and acetyl-L-carnitine, either individually or combined with other ingredients. The dosage in these supplements typically varies from about 3 mg to 5,000 mg. It's worth noting that the absorption rate of supplemental L-carnitine is approximately 14% to 18%, considerably less than that of dietary L-carnitine.