Choline is an essential nutrient for humans, providing the structural integrity of cell membranes, methyl metabolism, cholinergic neurotransmission, transmembrane signaling, and lipid and cholesterol transport and metabolism. Humans can synthesize choline in small amounts from ethanolamine and a methyl group donor such as methionine, folate, or vitamin B12, but synthesis rates are not adequate to meet the demand for choline in the body. Thus, choline was classified as an essential nutrient by IOM in 1998. Choline provides structure to cell membranes and facilitating transmembrane signaling as well as synthesis and release of acetylcholine. Choline functions as a component of phosphatidylcholine for intracellular signaling and hepatic export of very low-density lipoproteins and sphingomyelin for structural and signaling functions.
It is a precursor for the synthesis of acetylcholine, which is an important neurotransmitter involved in memory, muscle control, and many other functions. Choline functions as a precursor for the methyl group donor betaine, used as an organic osmolyte to adapt to osmotic stress by renal glomerular cells. Choline is required for the transport of fat from the liver; thus, symptoms of choline deficiency may include fat accumulation in the liver, “fatty liver”, and liver damage. Decreased choline stores and liver damage were indicated in healthy men fed choline-deficient diets containing adequate amounts of methionine, folate, and vitamin B12. In adults, choline-deficient diets for 42 days induced DNA damage and apoptosis in peripheral lymphocytes. For a recommendation of choline intake, AIs have been established based on dietary intake data from healthy individuals. The AIs for adult men and women are 550 and 425 mg/d, respectively. All natural fats contain some choline; thus, choline is found in a wide variety of foods. Dietary sources of choline include meats, whole grains, egg yolks, peanuts, and legumes. The vitamin occurs mostly in the form of phosphatidylcholine, also known as lecithin. Phosphatidylcholine is frequently added to foods as an emulsifier during processing by the food industry. Large quantities of choline have been associated with several adverse effects including a fishy body odor, nausea, vomiting, diarrhea, salivation, and increased sweating.
The fish body odor results from the increased presence of a breakdown product of choline called trimethylamine. Doses of choline in the 5–10 g/d range105 have been reported to reduce blood pressure (hypotension), which could result in faintness or dizziness. In 1998, the IOM established the UL for choline at 3.5 g/d for generally healthy adults, based on primarily preventing decreased blood pressure and secondarily preventing the fishy body odor. Decreased plasma choline concentrations have been reported after prolonged exercise; however, the mechanism that might account for a decrease in plasma choline is unknown. There are no conclusive results for beneficial effects of choline supplementation on exercise performance. Because choline is required for the synthesis of acetylcholine involved in muscle control during physical activity, choline deficiency or supplementation might have some effects on exercise performance. Therefore, more research is needed to investigate choline status of athletes and roles in physical activity.
