Arginine is a conditionally essential protogenic amino acid. Arginine is of interest to athletes because it is known to cause the release of significant amounts of growth hormone. Doses required for this effect are thought to be around 15 to 30 grams, a dose that can increase plasma levels of arginine five-fold. However, for arginine to be effective it must be administered intravenously. Similar doses of oral arginine are controversial because they only raise plasma levels around two-fold, and may therefore not cause significant release of growth hormone. Therefore the growth hormone releasing effects of oral arginine are not confirmed. However, arginine is also a building block of creatine and is required along with glycine for its synthesis. Some evidence supports a role for supplementary arginine and glycine in increasing the rate of creatine synthesis, which causes a small but significant increase in body stores of creatine. However, it is unclear if this brings with it a performance improvement. Oral arginine is also unlikely to be as effective as the supplementation with pure creatine monohydrate powder, which has a proven track record.
Other effects of arginine are known, and some may be of benefit to athletic performance and health. For example, evidence suggest that arginine is able to delay glucose disposal when taken concomitantly with oral glucose1. The amount of arginine (10g) administered was attainable in a high protein meal (equivalent to 0.78 kg of beef) and increased plasma concentrations of arginine by 64 %. It appears that this effect is not through a delay in gastric emptying, but may relate to the function of arginine as a precursor of nitric oxide. Nitric oxide is known to cause a reduction in gastrointestinal motility and this may account for the delayed glucose disposal. Nitric oxide also causes relaxation of blood vessels and can increase peripheral blood flow. Research supports a role for long-term oral arginine supplementation at improving insulin insensitivity in patients with type 2 diabetes2. Therefore arginine may delay glucose disposal through normalisation of endothelial dysfunction in peripheral tissues with concomitant improvements in insulin sensitivity.
