Glutamine (usually in the form of L-glutamine) is the most abundant free amino acid in human muscle . It is a non-essential amino acid because body can make enough glutamine for its regular needs, but may become conditionally essential in certain situations .
During various catabolic states glutamine homeostasis is placed under stress and can be impaired. Such states include starvation, prolonged exercise, infection, surgical trauma,… However, during short-term and high intensity exercise plasma glutamine levels remain unchanged or even elevated.
As we mentioned before athletes undergoing prolonged exercise (such as endurance races) are in danger because of increased risk of infection due to apparent immunosuppression. Lower plasma glutamine concentration due to prolonged exercise may contribute to impairment of the immune system.  It is used as a fuel by some cells of the immune system . It’s quite common for athletes to catch a cold after an event . Linda M. Castell et al.  investigated the effects of feeding glutamine after exhaustive exercise. Plasma glutamine levels were decreased by about 20% in runners 1 hour after marathon running. Oral supplementation of glutamine after exercise appeared to have a beneficial effect. Furthermore, in samples of those who received glutamine the ratio of T-helper/T-suppressor cells appeared to be increased.
Glutamine sources, RDA and precautions
Good sources of glutamine are beef, pork, milk, yogurt, cheese, cottage cheese, raw spinach, raw parsley, and cabbage. Doses of 500 grams up to 3 times daily, are generally considered safe. People with liver or kidney disease should not supplement with it.
- Brosnan JT (June 2003). “Interorgan amino acid transport and its regulation”. J. Nutr. 133 (6 Suppl 1): 2068S–2072S
- Walsh, Neil P., et al. “Glutamine, exercise and immune function: links and possible mechanisms.” Sports Medicine 26.3 (1998): 177-191.
- Castell, Linda M., and Eric A. Newsholme. “The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise.” Nutrition 13.7 (1997): 738-742.
- Castell, Linda M. “Glutamine supplementation in vitro and in vivo, in exercise and in immunodepression.” Sports Medicine 33.5 (2003): 323-345.
- Glutamine”. University of Maryland Medical Center. 2011-05-24. Retrieved 15 March 2013.