Choline is an essential nutrient and a major methyl donor that supports physiological processes from normal metabolism to neurological development in the fetus. Human beings obtain choline from two major sources: diet and endogenous production in the liver. The level of choline in the American diet varies substantially, with one study reporting a median intake of 284 mg/day compared with the recommended daily intake of 550 mg/day. Low-choline diets have been associated with health problems in humans and in mouse models, including non-alcoholic fatty liver disease, neural tube defects, hepatic cancer and an increased risk of breast cancer. Furthermore, common single nucleotide polymorphisms (SNPs) in several genes have been shown to affect choline production and metabolism. One notable example is the gene, PEMT, which is important in the endogenous de novo synthesis of phosphatidylcholine.