Glutamine is the most abundant amino acid (building block of protein) in the body. The body can make enough glutamine for its regular needs. But during times of extreme stress (the kind you experience after heavy exercise or an injury), your body may need more glutamine than it can make. Most glutamine is stored in muscles, followed by the lungs where much of the glutamine is made.
Glutamine is important for removing excess ammonia (a common waste product in the body). It also helps your immune system function and may be needed for normal brain function and digestion.
You can usually get enough glutamine without taking a supplement because your body makes it and you get some in your diet. Certain medical conditions, including injuries, surgery, infections, and prolonged stress, can lower glutamine levels. In these cases, taking a glutamine supplement may be helpful.
Athletes who train for endurance events (like marathons) may reduce the amount of glutamine in their bodies. It is common for them to catch a cold after an athletic event. Some experts think that may be because of the role glutamine plays in the immune system. For this select group of athletes, one study showed that taking glutamine supplements resulted in fewer infections. The same is not true, however, for exercisers who work out at a moderate intensity.
Infomation provided by the University of Maryland Medical Center, Read more at the following link http://umm.edu/health/medical/altmed/supplement/glutamine