Choline, Inositol, and Related Nutrients
CHOLINE, INOSITOL, AND RELATED NUTRIENTS
CHOLINE, INOSITOL, AND RELATED NUTRIENTS. Choline (2-hydroxy-N,N,N -trimethylethanaminium) and inositol (cis -1,2,3,5-trans-4,6-cyclohexanehexol) are water-soluble chemicals common in animal tissues and seeds of plants. Both compounds have been designated as water-soluble vitamins, and have also been referred to as "quasi-vitamins." Choline and inositol, while having distinctly different chemical structures, are often discussed together because they are integral components of phospholipids, some of the most important lipids in both plants and animals. Two of the most important functions of phospholipids are as structural components of cellular membranes and as second messengers, transmitting signals through cell surfaces into the cell.
Choline and the phospholipid phosphatidylcholine (PC) are typically high in foods containing relatively high amounts of fat and cholesterol such as beef liver, beef steak, and eggs. Plant-based foods follow the same generalization in that those containing relatively high levels of fat also contain relatively high levels of PC (peanuts, soybeans, and so on). All foods contain some choline or PC. "Lecithin" is a term describing the commercially available phospholipids, which can contain a variety of compounds including free fatty acids, triglycerides, and most of the phospholipids. Estimates of lecithin intake in the American population are approximately 6 g/day and an accompanying 0.6 to 1.0 g/day of choline. Adequate levels of intake are 0.125 to 0.15 g/day choline for infants, 0.2 to 0.375 g/day for children, 0.55 g/day for adult males, and 0.4 to 0.55 g/day for adult females. However, intake of choline and PC is probably decreasing in the United States because of our changing food habits. As Americans decrease intake of fats from animals, their intake of choline and PC will also decrease. Maximum daily recommended choline is 16 to 20 g/day. No maximum intake level has been identified for lecithin, but 40 g/day has been tolerated. Reactions to excessive intakes of choline include nausea, perspiring, anorexia, and cardiac arhythmias. Adults involved in strenuous exercise (such as participating in marathons) can experience significant decreases in plasma choline concentration (up to 40 percent), and there appears to be an enhancement of performance with supplemental choline intake. Commercially available sources of choline, lecithin, and PC are considered GRAS (generally recognized as safe) by the U.S. Food and Drug Administration.
Choline interacts with several drugs including anti-cancer drugs and nonsteroidal anti-inflammatory drugs (NSAIDs). Methotrexate is a relatively common drug in the fight against cancer and it leads to a decrease in liver choline concentrations and resulting increase in liver lipid concentrations. NSAIDs are known to facilitate changes in the gastrointestinal tract mucosal surface including perforations. Intake of PC improves such lesions.
Insufficient intake of choline can affect both acetylcholine and PC concentrations. Significant decreases in acetylcholine can result in a condition known as tardive dyskinesia (impaired movement and defective neural transmission), which can be corrected by increasing choline intake. There is also interest in choline as an aid in alleviating short-term memory loss (for example, Alzheimer's disease) and some concern that chronic inadequate intake of choline may facilitate the onset of Alzheimer's. Deficiencies of PC can result in increased lipid concentrations in liver (hepatic lipidosis), which is an analogous condition to cirrhosis of the liver caused by chronic alcoholism. If the deficiency persists, cirrhosis eventually leads to carcinoma. Choline deficiency also leads to infertility, bone abnormalities, hypertension, impaired kidney function, and decreased hematopoiesis. Similarly, deficiencies of inositol in laboratory animals leads to hepatic lipidosis and alopecia (hair loss). An inability to break down PI (Niemann-Pick disease) leads to enlarged spleen and liver, as well as mental development abnormalities.
Phospholipids are antioxidants commonly used in food products to inhibit oxidation and as emulsifying agents. Phosphatidylcholine can bind minerals such as iron and copper that are considered prooxidant minerals, or those that facilitate oxidation of lipids. Phosphatidylcholine can also help degrade hydroperoxides, or partial breakdown products of lipids and is commonly used for this purpose. The nitrogen-containing phospholipids phosphatidylethanolamine and phosphatidylserine (PI) are even more active than PC in protecting against oxidation of lipids. The two most common sources of phospholipids are soybeans and egg yolk. Lecithin from soybeans is more commonly used in commercial applications because of its lower cost. Soybean lecithin contains 50 to 70 percent phospholipid and is extracted with other prooxidants in vegetable oil processing. This process separates the oil from phospholipids, vitamin E, and other potentially beneficial nutrients. An older mechanism of lipid separation has been revived in the United States using simple pressing of soybean seeds to remove the oil instead of solvents. This results in oil with high levels of vitamin E and phospholipids. Lecithins containing higher concentrations of phospholipids and PC are also becoming available.
See also: Antioxidants ; Fats ; Lipids ; Minerals ; Soy ; Vitamins: Overview ; Vitamins: Water-soluble and Fat-soluble Vitamins.
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Paul B. Brown