Choline, unlike other B vitamins, which are synthesized by intestinal bacteria, is synthesized in the liver.

Choline is needed for the proper transmission of nerve impulses and is a constituent of acetylcholine, the major neurotransmitter. Choline is a structural element of cell membranes (as the chemical phosphatidylcholine) that promotes lipid transport and acts as a source of methyl groups (after it is transformed into betaine) for various chemical reactions in the body. Choline acts like folic acid, TMG (trimethylglycine), and SAMe (S-adenosylmethionine) to promote methylation.

It appears that phosphatidylcholine is presumed to be responsible for the medicinal effects of choline supplementation.

Choline is also useful for proper functioning and regulation of the liver and gallbladder. This vitamin aids in hormone production and minimizes fat accumulation in the liver by regulating fat and cholesterol metabolism.

In people, choline (or lecithin) supplementation has been recommended for the treatment of a variety of disorders, including elevated blood cholesterol, liver disease, and psychological and neurological disorders (such as Tourette's syndrome, Alzheimer’s disease, and bipolar disorder). The evidence supporting the treatment of these disorders with choline is slim; since supplementation is safe and some studies have shown benefit, the use of choline is often recommended.

In pets, choline is used as a natural therapy for seizures and cognitive disorder. There is a good evidence for its use in dogs with seizures and cognitive disorder; anecdotal evidence suggests effectiveness in cats with these medical problems as well. Choline is also recommended for pets with liver and gallbladder disease, especially those resulting from fat accumulation in the liver) fatty liver disease called hepatic lipidosis). Pets with high levels of blood cholesterol (as seen in dogs with hypothyroidism and in the genetic disorder hyperlipidemia in Miniature Schnauzers) may also respond to choline supplementation, although controlled studies are lacking. However, choline and methionine should not be used if hepatic encephalopathy (acidosis and brain depression) is present.

Since choline is present in myelin sheaths (the sheath surrounding nerves) as sphingomyelin, supplementation of pets with demyelinating disorders (such as canine degenerative myelopathy) may be indicated, although once again controlled studies are lacking.

Choline is present in the diet as lecithin, choline, or sphingomyelin.

Choline can be found in egg yolks, lecithin, meat, milk, whole grains, soybeans, soy, and natural fats.

The AAFCO recommendation for choline is 1200 ppm for dogs and 2400 ppm for cats.

Choline supplementation is believed to be generally safe. While rarely reported, side effects such as anemia may be seen in dogs receiving three or more times the apparent choline requirement (anemia has been reported in dogs receiving 150 mg of choline). However, many holistic veterinarians use high levels of choline in pets with cognitive disorder without apparent ill effects. Monitoring pets receiving high levels of choline for anemia seems warranted.