Glutamine is the most common and important free amino acid in the human body. Given the body's ability to make glutamine, people might be expected to never run low on glutamine. Nonetheless, people sometimes have a glutamine deficit. There are at least two situations in which this occurs -- after serious damage to the body and after strenuous physical exercise. A third possibility is fighting a cold.
Glutamine is a major fuel for the immune system and the intestines, and a glutamine shortage impairs their functioning. In particular, bacteria are more likely to cross the intestinal walls into the blood during a glutamine shortage. Glutamine is a neurotransmitter in the brain, and it is a precursor to other neurotransmitters, so glutamine levels might affect the brain. When there is a glutamine shortage, the muscles are broken down to release glutamine to the rest of the body, so a glutamine shortage can also lead to muscle wasting. Finally, even though glutamine is not a component of glutathione, it appears to be needed in at least some cells to make glutathione. (Glutathione is an important antioxidant.)
As explained in the 1994 book Glutamine: The Ultimate Nutrient, people in a hospital setting benefit from glutamine supplements. This occurs for people who have experienced major surgery, multiple traumas, and burns. It also occurs for very low birth weight infants. Studies are not always consistent -- they differ in which benefits are found -- but glutamine has been found to reduce the probability of an infection or disease, to decrease the duration or expense of the hospital stay, and to decrease the amount of muscle wasting. In some studies, it has even increased the probability of survival. The advantage for glutamine occurs even though patients are receiving adequate protein.
Another factor increases the need for glutamine -- parenteral feeding, in which patients are fed intravenously rather than eating their food. This places a strain on the intestines, increasing the need for glutamine. Meanwhile, parenteral food usually does not contain glutamine.
When used in the hospital setting, people usually take about 20 grams of glutamine a day. This much glutamine might not be needed, but it seems to be safe.
Like any other rapidly growing cell, cancer cells tend to use glutamine. One attempted strategy for treating cancer is to deprive the cancer of glutamine. Unfortunately, the glutamine deprivation seems to be harder on the patient's body than on the cancer. There is no indication that glutamine supplements increase cancer, and in fact glutamine has been found to provide some protection for patients receiving chemotherapy.
Research, mostly on rats, suggests that glutamine decreases the metabolic breakdown of methotrexate, making it more powerful. Furthermore, glutamine causes cancer cells to absorb more methotrexate. In one study on humans, alas with no control group, glutamine apparently didn't improve the effectiveness of methotrexate but did substantially reduce the side effects.
Strenuous exercise lowers the blood concentration of glutamine. Sometimes the glutamine level does not recover before the next training session. Several studies have suggested that athletes in the overtraining syndrome have chronically low levels of glutamine. The overtraining syndrome occurs when an athlete's performance becomes worse, despite continued training. The athlete is more prone to infections and injuries and might have a variety of other problems, including digestive problems and a lack of motivation. Anaerobic exercise depletes glutamine more than aerobic exercise.
Most of the evidence concerning glutamine and athletes is circumstantial -- glutamine levels are known to be sometimes lower in athletes, and many of the problems athletes experience can be explained as a glutamine deficiency. Only one study has actually given glutamine to athletes to observe its effects, finding that taking glutamine after running a marathon leads to fewer upper respiratory infections.
Just 2 grams of glutamine produces a noticeable rise in glutamine blood levels. As a guess, athletes probably do not need as much glutamine as hospital patients.
People with a cold have lower levels of glutamine. Presumably glutamine levels are depleted by the increased activation of the immune system to fight the cold. This decrease might impair the effectiveness of the immune system, though there is no evidence to confirm this possibility.
Droge talks about two syndromes. The first is a deficit in cysteine (another amino acid), which leads to a deficit in glutamine. According to Droge, the pattern of low cysteine and glutamine occurs in major surgery, major trauma, infections, burns, cancer, Crohn's disease (a problem of the intestines), chronic fatigue, overtraining, and the "late asymptomatic" stage of HIV (which is just prior to the major outbreak of AIDS). The solution is to take cysteine.
The second syndrome starts with the production of lactate, which leads to normal cysteine but low glutamine. This pattern is found in cancer, old age, and athletes engaging in strenuous anaerobic exercise. Droge's theory is based on the production of urea versus glutamine in the liver.
Glutamine helps the symptoms of sickle cell anemia.
