ABSTRACT
Glutamine was originally classified as a nonessential amino acid. However, since the 1990s there has been increasing evidence that glutamine becomes “conditionally essential” in specific conditions of stress, including strenuous exercise. During physiological stress such as exercise, an increase in the concentration of cortisol in the blood can initiate proteolysis of muscle proteins, transamination of amino acids to glutamate, and the synthesis and increased release of glutamine. The normal resting, fasting plasma concentration of glutamine in humans is 500–600 µM. Different glutamine assays can produce different data, and it is unwise to compare the absolute values of one research group with another unless they have used identical assays. Several exercise studies using glutamine supplementation have found no, or limited, effects on specific aspects of immune function. Some of the effects on the immune system observed are reduced neutrocytosis and increased circulating interleukin-6.
