Updated: May 8
Arginine plays so many roles in sports nutrition that I hesitate to give it another place, lest this simple amino acid sounds too good to be true. But the evidence is so strong that arginine improves immunity that I have to conclude it is one of its top benefits.
Some researchers may object that it was established 50 years ago that arginine is not even an essential nutrient in horses. True for pleasure horses, but not true for horses whose body is under the sort of stress that threatens nitrogen balance or immunity. In studies of stressed horses, with impaired immunity, arginine supplements improve the action of T-lymphocytes and the delayed hypersensitivity response.
Arginine also works with postoperative horses and critical care horses to improve immune responses. And in healthy horses, recent studies show that 30 grams of arginine per day for 3 days improved immune responses to various deliberate challenges. The unique action of arginine is not related to deficient levels of arginine in these horses but to another mechanism entirely.
Although not yet proven by controlled studies, I'll lay my money that arginine stimulates immunity by the same mechanism that it stimulates muscle growth, that is, its action in releasing growth hormone from the anterior pituitary. In several horse studies, arginine fails to stimulate immunity if the anterior pituitary is blocked. This is not the whole story, however, as new research also shows the unique actions of arginine in various immune pathways. These findings make arginine an important nutrient for optimum sports performance.
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