Yet, research has yet to confirm their benefits in athletes. Also questionable are glutamine supplements. Glutamine, an amino acid that enhances immunity, has been touted to be the athletes' aid to stronger recovery and immune function. According to Dr. Nieman, blood levels of glutamine drop with exercise, but even marathon-type exercise does not sufficiently deplete the body's large stores of glutamine enough to diminish immune function and create a need for athletes to take glutamine supplements. The one nutritional practice that does enhance immune function is to consume carbohydrate during hard exercise that lasts longer than 90 to 120 minutes.
Carbohydrates break down into glucose, and glucose is the major fuel for immune cells.
Low blood glucose also triggers the release of stress hormones that suppress immune function. Hence, a drop in blood sugar during prolonged, intensive exercise can reduce immune function. A second immune booster is exercise itself. For example, exercise boosts the level of natural killer cells that suppress certain types of cancer. For example, runners who run more than 60 miles per week have double the risk of getting sick compard to those who run less.