Choline is essential to eat, yet officially it is not a vitamin
Your liver makes choline, just not enough of it. The shortfall has to come from eggs, meat, fish, beans and similar foods, because the body needs choline to build cell membranes and the neurotransmitter acetylcholine. Despite that, it has never been formally classed as a vitamin.
Chemically, choline is a small positively charged ion: an ethanolamine unit carrying three methyl groups on one nitrogen atom. It forms salts such as choline chloride and choline bitartrate. As a free base it absorbs water from the air and turns into a colourless, syrupy liquid smelling of trimethylamine, the compound behind a fishy odour. Historically it was obtained by breaking down lecithin; industrially, choline chloride can be made by reacting trimethylamine with 2-chloroethanol.
In animals, choline-containing phospholipids are built into the membranes of cells and their internal compartments, and into very low-density lipoproteins. Choline also feeds two crucial molecules. One is acetylcholine, which carries signals for muscle control and many nervous-system functions. The other is S-adenosylmethionine, a general-purpose donor of methyl groups used throughout metabolism. It plays a part in early brain development, gene expression and cell signalling as well.
Humans make some choline from scratch, mainly in the liver through the PEMT pathway, where an enzyme transfers three methyl groups onto phosphatidylethanolamine to produce phosphatidylcholine. Plants take a different route, starting by stripping a carbon dioxide group from the amino acid serine. Because human production falls short, diet matters: liver, egg yolks, dairy, peanuts, nuts, seeds, poultry and cruciferous vegetables are good sources. Breast milk contains choline, and manufacturers routinely add it to infant formula.
Getting too little can cause non-alcoholic fatty liver disease and muscle damage. Getting far too much, above about 7.5 grams a day, can bring low blood pressure, sweating, diarrhoea and a fishy body odour, since metabolising choline releases trimethylamine.
Source: Choline
