Discovered in 1905, L-carnitine is a nitrogen-containing, short-chain carboxylic acid. Technically, it is not an amino acid, but a water-soluble, vitamin-like compound that is readily synthesized in the body from the amino acids lysine and methionine and Vitamin C. In mammals, L-Carnitine is produced in liver, kidney and brain tissue and stored in skeletal and cardiac muscle. In the cell, L-carnitine functions in a three-part enzyme complex that is responsible for transporting long-chain fatty acids across the mitochondrial membrane into the interior where they are converted into energy for the cell.
Because it can be manufactured in the body, carnitine is not an essential nutrient. It is sometimes considered essential, however, because a dietary deficiency may cause adverse side effects under certain circumstances. Carnitine deficiencies are rare in most industrialized nations. When they do occur, they are generally due to a genetic disorder -- Carnitine Palmitoyl Transferase (CPT) deficiency -- that prevents the body from processing carnitine properly. In adults, this manifests as muscle weakness and low serum levels of ketones. In infants, this disorder often leads to heart arrhythmia resulting in death.
Dietary carnitine comes from sources such as meat, particularly beef, sheep, and lamb. Other animal products, such as milk, cheese, and poultry, contain lesser amounts, while fruits and vegetables have negligible amounts. A diet with sufficient quantities of lysine and methionine will provide the necessary building blocks for the body to synthesize and maintain sufficient levels of carnitine.
In recent years, a number of scientific studies have shown that supplements of carnitine may help slow the progression of Alzheimer's disease. These studies confirmed the promise for therapeutic applications of an ester form of carnitine, acetyl-L-Carnitine, a more potent form of carnitine. Researchers had observed that this compound readily crosses the blood- brain barrier and improves neuronal energetics and repair mechanisms while modifying acetylcholine production in the central nervous system.