Choline Dietary Supplements To Help Prevent Cancer And Improve Memory

Choline is an essential B vitamin that functions as a precursor for the neurotransmitter acetylcholine and as a bull ding block for phospholipids in cellular membranes and lipoproteins and for the methyl donor betaine. It can be manufactured in the body (from the amino acid methionine), although whether it can be made in sufficient amounts for optimal health is a matter of some debate. Folk acid and vitamin B12 are also needed to process choline. Choline plays a role in liver function, cardiovascular health, and brain development {as an amine precursor for the neurotransmitter acetylcholine). In 1998, the Food and Nutrition Board (FNB) of the National Academy of Sciences established adequate intake (AI) levels for choline of 550 mg/day for men and 425 mg/day for women. In setting AI levels for choline, the FNB also noted that "there are few data to assess whether a dietary supply of choline is needed at all stages of the life cycle and it may be that choline requirement can be met by endogenous synthesis at some of these stages" (National Academy of Sciences, 1998).

Nevertheless, numerous choline-based dietary supplements are marketed with claims for improving memory, protecting the cardiovascular system, preventing cancer, and delaying fatigue.

Choline is found in the diet in milk, liver, eggs, peanuts, and soybeans, where it is available as free choline or is bound as esters such as phosphocholine, glycerophosphocholine, sphingomyelin, or phosphatidylcholine. Choline can also be found in various "brain support" supplements, including lecithin (phosphatidylcholine). Although adequate maternal choline intake has been shown to be important for fetal brain development during pregnancy, dietary sources of choline (eggs and peanuts) are the preferred method of increasing choline intake for pregnant women. Among endurance athletes, choline supplements may be warranted because intake of choline is presumed low (owing to reliance on a high-carbohydrate diet for energy) and loss of choline following exercise is greater. Although it is important to ensure an adequate daily intake of choline to support normal nerve function and cell membrane structure, it is unlikely that additional choline in supplement form will boost mental acuity or endurance exercise performance (common product claims).

Choline is required to make essential membrane phospholipids, as a precursor for the biosynthesis of the neurotransmitter acetylcholine, and as an important source of labile methyl groups in numerous methylation reactions throughout the body (Zeisel et al., 1991). The AI levels for choline (425-550 mg/day) are based on the prevention of liver damage as assessed by serum alanine aminotransferase levels. Healthy humans fed a choline-deficient diet develop impaired methylation capabilities and liver dysfunction within 3 weeks, suggesting that choline is an essential nutrient (Jacob et al., 1995; Zeisel etal., 1991). Choline participates in lipid (fat) transport in the body and may reduce accumulation of fat in the liver (Zeisel et al., 1991). As a dietary supplement and ergogenic aid, however, claims surrounding choline are mostly the result of its role as a component of acetylcholine (the neurotransmitter needed for conduction of nerve signals and brain function). Claims in this area typically involve mental performance, memory, and reaction time.

During pregnancy, the mother's choline intake may influence memory and brain development in the growing fetus. Studies on choline and lecithin supplementation clearly show an increase in blood choline levels following supplementation with 1-5g of choline (or5~15 g of lecithin). Despite the wide range of commercial products claiming choline as a memory aid, no studies support that role. Studies of choline supplementation for fat metabolism have shown that choline does not increase fat metabolism; moreover, choline appears to reduce serum and urinary carnitine levels an effect that could be expected to reduce overall fat metabolism (Daily and Sachan, 1995; Hongu and Sachan, 2003).

Choline has also been studied in humans as an aid to endurance exercise. Because plasma choline levels are known to fall after strenuous exercise, it has been suggested that choline supplementation might delay fatigue and enhance performance by increasing the synthesis of acetylcholine for muscle contractions (Spector et al., 1995; Warber et al., 2000). Studies of choline supplementation in athletes, however, have been disappointing. In one study of soldiers, 8.425 g of choline citrate given before and midway through a 4-hour treadmill exercise increased plasma choline levels by 128% but had no significant effect on any performance measurement (Warber et al., 2000). In another study, trained cyclists were supplemented with 2.43 g of choline bitartrate 1 hour before either a brief supramaximal (150% maximum power) or prolonged submaximal (70% maximum power) exercise test. Choline supplementation increased plasma choline levels 37-52%, but no significant changes were noted for measures of fatigue or exercise performance for either test (Spector et al., 1995).

The AI levels for choline are 550 mg/day for men and 425 mg/day for women. The upper limit (UL) for adults is 3.5 g/day. Choline has a high margin of safety as a dietary supplement, and consumers can select foods with higher choline by looking for FDA-approved nutrient content claims on products with preexisting or added choline, such as this: "Good source of choline. Contains 55 mg of choline per serving, which is 10% of the daily value for choline (550 mg)." No adverse effects of choline supplements have been noted at levels of 1-2 g, whereas doses closer to 3-5 g {above the UL of 3.5 g/day) may be associated with side effects such as diarrhea, nausea, and abdominal discomfort. Anecdotal reports have been made of "fishy body odor" in people consuming high daily doses of choline or lecithin.

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