Supplement research

Glutamine

What is Glutamine?

Glutamine is a non-essential amino acid. It is the most abundant amino acid in muscle and plasma. Whereas most amino acids are metabolised in the liver, the majority of glutamine metabolism occurs in the muscle. Glutamine is considered important for many activities of the immune system.

Proposed Benefits of Glutamine

Glutamine is proposed to improve immune function.

Mechanism of Action of Glutamine

Glutamine is an important energy substrate for cells of the immune system.  It is also been proposed that the availability of glutamine regulates various aspects of the immune system.

Research on Glutamine

Plasma glutamine concentrations do fall as a result of prolonged exercise or other catabolic states such as trauma or surgery. It is controversial however, as to the clinical significance of the decline in plasma glutamine concentrations (1).

Glutamine supplementation for those with immunosuppression
Much of the research on glutamine has been carried out in individuals who are in an immunocompromised state e.g. burn trauma, following surgery. Many of these studies suggest that in situations where a patient's immune system is compromised the requirement for glutamine is increased and subsequent supplementation with glutamine can improve immune status and reduce the risk of infection (2-8). However, some of these studies are difficult to interpret because the treatment has included several potential "immunonutrients", making it difficult to contribute immune effects solely to glutamine (2,7).

Glutamine supplementation for physically active individuals
Although there is evidence to support glutamine supplementation to prevent or treat infection in immunosuppressed states, how this may translate to athletes is controversial.
As muscle provides an important source of glutamine and research has shown that plasma glutamine levels fall during prolonged exercise (9), it is thought that any acute reductions in muscle glutamine concentrations would reduce the rate of muscle protein synthesis and potentially limit glutamine availability to the immune system.
Also, some investigators have hypothesised that overtraining may reduce the release of glutamine from the muscle thus contributing to the lower plasma glutamine concentrations reported in athletes diagnosed with over-training syndrome (10,11). Also athletes showing symptoms of chronic fatigue may have low levels of plasma and muscle glutamine concentrations (12). However whether these alterations in glutamine levels directly affect immune function in athletes is unclear. Mackinnon et al showed that although overtrained swimmers had lower plasma glutamine concentrations, there was no difference in plasma glutamine concentration between swimmers who developed URTI and those who remained healthy (10).
The recommendation that glutamine is beneficial to athletes is based on the premise that glutamine concentration in the plasma and muscle limit the function of the immune cells. However there is evidence to suggest that the decrease in plasma and muscle glutamine as a result of exercise may not be physiologically significant. A study by Castell et al showed that oral glutamine supplementation (5g) consumed immediately after and two hours after the completion of a marathon reduced rates of upper respiratory tract infections (URTIs) (13). However many other studies have failed to find any beneficial effect of glutamine supplementation (10,14-18). There is not yet convincing evidence to support the hypothesis that the prevention of exercise-induced reductions in glutamine levels will alter immune changes.

Rating of Efficacy for Glutamine

7/10 Rating for efficiency for improving immune status in those with in an immunocompromised
state  e.g burn trauma

5 1/2 /10  Rating of efficiency for improving immune status in athletes and reducing risk of infection and disease is. More research is required.

References

1.  Buchman A.L. Glutamine: commercially essential or conditionally essential? A critical appraisal of the human data. Am J Clin Nutr. 74:25-32, 2001.
2.  Gottschlich M.M., Jenkins M. and Warden G.D. Differential effects of three enteral dietary regimes on selected outcome variables in burn patients. JPEN. 14:225-236, 1990.
3.  Houdijk A.P., Rijnsburger E.R. and Jansen J. Randomised trial of glutamine-enriched enteral nutrition on infectious morbidity in patients with multiple trauma. Lancet. 352:772-776, 1998.
4.  Morlon B.J., Stehle P. and Wachtler P. Total parenteral nutrition with glutamine dipeptide after major abdominal surgery. Ann Surg. 227:302-308, 1998.
5.  Ogle C.K., Ogle J.D. and Mao J.X. Effect of glutamine on phagocytosis and bacterial killing by normal and pediatric burn patient neutrophils. JPEN. 18:128-133, 1994.
6.  Parry-Billings M., Evans J., Calder P.C. and Newsholme E.A. Does glutamine contribute to immunosuppression after major burns? Lancet. 336:523-525, 1990.
7.  Saffle J.R., Wiebke G., Jennings K., Morris S.E. and Barton R.G. Randomized trial of immune-enhancing enteral nutrition in burn patients. J Trauma. 42:793-800, 1997.
8.  Yoshida S., Matsui M., Shirouzu Y., Fujita H., Yamana H. and Shirouza K. Effects of glutamine supplements and radiotherapy on systemic immune and gut barrier function in patients with advanced oesophageal cancer. Ann Surg. 227:485-491, 1998.
9.  Rennie M.J., Edwards R.H.T. and Krywawych S. Effect of exercise on protein turnover in man. Clin Sci. 61:627-639, 1981.
10.  Mackinnon L.T. and Hooper S.L. Plasma glutamine concentration and upper respiratory tract infection during overtraining in elite swimmers. Med Sci Sports Exerc. 28:285-290, 1996.
11.  Parry-Billings M., Budgett R. and Koutedakis Y. Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system. Med Sci Sports Exerc. 24:1353-1358, 1992.
12.  Rowbottom D.G., Keast D., Goodman C. and Morton A.R. The haematological, biochemical and immunological profile of athletes suffering from the overtraining syndrome. Eur J Appl Physiol. 70:502-509, 1995.
13.  Castell L.M., Poortmans J.R. and Newsholme E.A. Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol. 73:448-490, 1996.
14.  Antonio J., Sanders M.S., Kalman D., Woodgate D. and Street C. The effects of high-dose glutamine ingestion on weightlifting performance. Journal of Strength & Conditioning Res. 16:157-160, 2002.
15.  Rohde T., Asp S., MacLean D. and Pedersen B.K. Competitive sustained exercise in human, lymphokine activated killer cell activity - an intervention study. Eur J Appl Physiol. 78:448-453, 1998.
16.  Rohde T., Krywkowski K. and Pedersen B.K. Glutamine, exercise, and the immune system - is there a link? Exerc Immunol Rev. 4:49-63, 1998.
17.  Rohde T., MacLean D. and Pedersen B.K. Effect of glutamine supplementation on changes on the immune system induced by repeated exercise. Med Sci Sports Exerc. 30:856-862, 1998.
18.  Walsh N.P., Blannin A.K., Bishop N.C., Robson P.J. and Gleeson M. Effect of oral glutamine supplementation on human neutrophil lipopolysaccharide-stimulated degranulation following prolonged exercise. In J Sport Nut Exerc Metab. 10:39-50, 2000.