Any of a class of phospholipids (also called phosphatidyl cholines) important in cell structure and metabolism. They are composed of phosphate, choline, glycerol (as the ester), and two fatty acids. Various fatty acids pairs distinguish the various lecithins. Commercial lecithin, a wetting and emulsifying agent used in animal feeds, baking products and mixes, chocolate, cosmetics and soap, insecticides, paint, and plastics, is a mixture of lecithins and other phospholipids in an edible oil.

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Organic compound related to vitamins in its activity. It is important in metabolism as a component of the lipids that make up cell membranes and of acetylcholine. It is also important as a source of chemical raw materials for cells and in transport of fats from the liver. It is usually classified with the B vitamins (see vitamin B complex) because it resembles them in function and in its distribution in foods. In humans it is interconvertible with certain other compounds, such as methionine, so deficiency does not lead to disease, but some other animals need it in their diet. Choline has various uses in medicine, nutrition, and the processing of foods and feeds.

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