By Stephen Daniells Nutra Ingredients USA
Supplements of the amino acid L-arginine may not produce metabolic or hormonal enhancement for fit young men at rest, says a new study from Canada.
Scott Forbes and Gordon Bell from the University of Alberta report that while low and high doses of the amino acid did raise blood levels in athletes at rest, neither dose appeared to impact levels of nitric oxide, growth hormone, insulin, or insulin-like growth factor-1.
L-arginine is a precursor for nitric oxide, a potent vasodilator (blood vessel dilator) that improves blood flow. The amino acid has also been reported to raise blood levels of growth hormone.
The new study, which involved 14, active, physically twenty-something men, is reported to be the first to assess the effects of L-arginine on various hormonal and metabolic markers.
“Despite the increase in L-arginine and the absence of side effects, the doses used in our study had little effect on certain metabolites or hormonal concentrations at rest,” wrote the researchers.
The study’s findings were described as “not surprising” by Douglas Kalman PhD, RD, FACN, director, BD - Nutrition & Applied Clinical Trials, Miami Research Associates.
Commenting independently on the results, Dr Kalman told NutraIngredients-USA that previous studies where a ‘blood effect’ of arginine has been reported have, for the most part, been done in people with vascular disease. “Studies in ‘normal healthies’ have not yielded the same,” he added.
Fourteen men described as active and physically fit, but who did not take nutritional supplements were recruited. The men were assigned to receive placebo, or a single low or high dose of L-arginine equivalent to 0.075 and 0.15 grams of L-arginine per kg of body mass, respectively.
Forbes and Bell report that both doses produced similar increases in blood levels of the amino acid, but neither affected the various hormonal and metabolic measures in healthy, young, physically active males at rest.
"There's a lot of money in nutritional supplements," said Forbes adds. "The industry might not be too happy when they see the results at rest, but who knows, it may be different with exercise."
Forbes told NutraIngredients-USA that he is just finishing two exercise studies with trained athletes. One study involves L-arginine supplementation prior to resistance exercise and the other study involves L-arginine supplementation prior to 60 minutes of sub-maximal cycling.
“L-arginine seems to be a very popular supplement and little is known about the effects of the supplement alone on exercise performance,” said Forbes. “Several studies and supplements combine L-arginine with other ingredients making causal claims difficult.”
Source: Applied Physiology, Nutrition and Metabolism
Volume 36, Issue 3, Pages 405-411
“The acute effects of a low and high dose of oral L-arginine supplementation in young, active males at rest”
Authors: S.C. Forbes, G.J. Bell