Choline is an essential nutrient that is soluble in water . It has many complex tasks in the human body. It is needed for lipid transport from the liver, cell-membrane signalling, it is precursor molecule for the neurotransmitter acetylcholine and it serves as a major source of methyl groups (methyl-group metabolism) . It is often added to b-complex vitamins. Choline is not only derived from the diet but is synthesised in liver [by phosphatidylethanolamine N-methyltransferase (PEMT)] as well.
Can Choline Improve Exercise Performance?
Choline is marketed to improve physical endurance by increased fat lipolysis and acetylcholine production which may increase muscle contraction and prevent decrement in performance .
In a double-blind, cross-over study in cyclists, 2,34 grams of choline bitartrate showed no improvements in performance . Another well-designed study conducted on soldiers which involved exhaustive exercise also failed to show performance benefits . Although choline citrate (8.425 g) / choline bitartrate (2,34 g) supplementation increased plasma choline, it failed to delay fatigue [2,4,5]. A few other placebo-controlled trials also failed to show an increase in anaerobic or/and aerobic performance with choline supplementation [6,2].
However, studies suggest that lower than recommended choline intake (~50% of AI) for more than one month may negatively affect change in strength associated with resistance exercise . While higher (~118% of AI) intake does not provide additional benefits on strength gains.
An interesting find by Kohlmeier and Dong suggests that men susceptible to exercise-induced muscle damage are more likely to have low choline intake than men with more resilient muscles. Both very low choline intake and intense exercise in healthy men can trigger peak muscle soreness a few days later and a rise of creatine kinase activity in peripheral blood indicating muscle damage. 
It has also been promoted as a weight loss supplement. However, there are no human trials to support this claim . Evidence does not support claims that choline reduces body adipose tissue, neither does high dose increase fat metabolism in humans [2,3].
When choline deficient, most adults develop signs of organ dysfunction (fatty liver or muscle damage) . Choline deficiency also causes low levels of methionine, which increases homocysteine (a risk factor for cardiovascular disease) . Women are less likely to develop such dysfunctions because estrogen increases the PEMT gene which makes more of needed choline in the liver . Studies are also showing that subjects who developed signs of organ dysfunction had normal organ function restored after choline has been added to their diet .
Choline Side Effects
In studies conducted the side effects were mostly minor and included gastrointestinal upset and fishy body odour .
Zeisel, Steven H., and Kerry‐Ann Da Costa. “Coline: an essential nutrient for public health.” Nutrition reviews 67.11 (2009): 615-623.
- Castell, L. M., et al. “A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 9.” British journal of sports medicine 44.8 (2010): 609-611.
- Hongu, Nobuko, and Dileep S. Sachan. “Carnitine and chline supplementation with exercise alter carnitine profiles, biochemical markers of fat metabolism and serum leptin concentration in healthy women.” The Journal of nutrition 133.1 (2003): 84-89.
- Spector, Sidney A., et al. “Effect of cholne supplementation on fatigue in trained cyclists.” Medicine and science in sports and exercise 27 (1995): 668-668.
- Warber, John P., et al. The Effect of Cholin Supplementation on Physical and Mental Performance of Elite Rangers. Army Research Inst Of Environmental Medicine Natick MA, 1997.
- Warber, John P., et al. “The effects of cholin supplementation on physical performance.” International journal of sport nutrition and exercise metabolism 10.2 (2000): 170.
Zeisel, Steven H. Annual review of nutrition 26 (2006): 229.
- Fischer, Leslie M., et al. The American journal of clinical nutrition 85.5 (2007): 1275-1285.
Mason, Bryan C., and Mark E. Lavallee. “Emerging Supplements in Sports.” Sports Health: A Multidisciplinary Approach 4.2 (2012): 142-146.
- Lee, Chang Woock. The Effects of Dietary Choline on Muscle Responses to Resistance Exercise in Older Adults. Diss. 2016.
- Kohlmeier, Martin, and Olivia Dong. “Exercise-induced muscle damage in healthy men with low choline intake.” The FASEB Journal 30.1 Supplement (2016): 678-15.