Choline: an essential dietary nutrient?

Choline (trimethyl-beta-hydroxyethylammonium) is a quaternary amine which is widely distributed in plants and animals. It contains three methyl groups which are important in a number of metabolic reactions, including the synthesis of methionine and carnitine. Choline is also a component of the phospholipids phosphatidylcholine and sphingomyelin, important constituents of all cell membranes. Finally, choline is necessary for the synthesis of the neurotransmitter acetylcholine. Although this compound is considered an essential nutrient in numerous mammalian species, this has not been established for humans.