Choline is a water-soluble essential nutrient that is usually grouped with the B-complex vitamins. Choline appears in the head groups of phosphatidylcholine and sphingomyelin, two classes of phospholipid that are abundant in cell membranes. Choline is the precursor molecule for the neurotransmitter acetylcholine, which is involved in many functions including memory and muscle control.
Inositol is a carbohydrate, though not a classical sugar. It was once considered as a member of the vitamin B complex, however\ because it is produced by the human body from glucose, it is not classified as an essential nutrient. Inositol, like choline, is a constituent of phospholipids and is involved in electrical signal transduction through cell membranes.
Choline was discovered by Adolph Strecker in 1864 and chemically synthesized in 1866. In 1998, choline was classified as an essential nutrient by the Food and Nutrition Board of the Institute of Medicine (USA). Choline's importance as a nutrient was first appreciated in the early research on insulin functions when choline was found to be the necessary nutrient in preventing fatty liver. In 1975, scientists discovered that the administration of choline increased the synthesis and release of acetylcholine by neurons. These discoveries lead to the increased interest in dietary choline and brain function.
Choline has four main functions in the body: as phosphatidylcholine, it works as a structural element in biological membranes and promotes lipid transport through cell membranes. As acetylcholine, it is a neurotansmitter and can also be involved in transmethylation reactions (source of methyl groups).
All natural fats contain some choline. Meat, eggs, cereal grains and legumes are best sources of choline. Inositol is usually synthesized by the liver but is also found in fruits, beans, grains and nuts.