Choline is a basic constituent of lecithin that is found in many plants and animal organs. It is important as a precursor of acetylcholine, as a methyl donor in various metabolic processes, and in lipid metabolism. Choline is now considered to be an essential vitamin. While humans can synthesize small amounts (by converting phosphatidylethanolamine to phosphatidylcholine), it must be consumed in the diet to maintain health. Required levels are between 425 mg/day (female) and 550 mg/day (male). Milk, eggs, liver, and peanuts are especially rich in choline. Most choline is found in phospholipids, namely phosphatidylcholine or lecithin. Choline can be oxidized to form betaine, which is a methyl source for many reactions (i.e. conversion of homocysteine into methionine). Lack of sufficient amounts of choline in the diet can lead to a fatty liver condition and general liver damage. This arises from the lack of VLDL, which is necessary to transport fats away from the liver. Choline deficiency also leads to elevated serum levels of alanine amino transferase and is associated with increased incidence of liver cancer.