Choline is an essential nutrient for humans and many other animals. Choline occurs as a cation that forms various salts (X− in the depicted formula is an undefined counteranion). To maintain health, it must be obtained from the diet as choline or as choline phospholipids, like phosphatidylcholine. Humans and most animals make choline de novo, but production is insufficient in humans and most species. Choline is often not classified as a vitamin, but as a nutrient with an amino acid–like metabolism. In most animals, choline phospholipids are necessary components in cell membranes, in the membranes of cell organelles, and in very low-density lipoproteins. Choline is required to produce acetylcholine – a neurotransmitter – and S-adenosylmethionine, a universal methyl donor involved in the synthesis of homocysteine.Symptomatic choline deficiency – rare in humans – causes nonalcoholic fatty liver disease and muscle damage. Excessive consumption of choline (greater than 7.5 g/day) can cause low blood pressure, sweating, diarrhea and fish-like body odor due to trimethylamine, which forms in its metabolism. Rich dietary sources of choline and choline phospholipids include hen egg yolk, wheat germ, and meats, especially organ meats, such as beef liver.