What are the advantages and disadvantages of using the supplement nitric oxide?
Nitric oxide is a gas naturally found in the body; its function is conveying information between cells. One of its main jobs is increasing blood flow by dilating blood vessels, and that's why it's sometimes given in supplement form to heart patients, orally and intravenously. In at least one study it's been shown to be effective for lowering blood pressure.
The supplement one takes is not nitric acid but arginine (or L-arginine), an amino acid that's a building block for the production of the gas. (Arginine is in foods such as spinach, sesame seeds, crab, shrimp, and white meat turkey.) Since some studies have linked taking arginine supplements to increased blood flow and human growth hormone production, some athletes — especially bodybuilders — are convinced that taking oral arginine supplements will improve their performance and strength.
The supplements don't appear to have any serious side effects, says Dr. Gary Green, a clinical professor in the UCLA School of Medicine's division of sports medicine (although he cautions that other supplements combined with arginine could cause a reaction). But some studies, he adds, beg to differ about those performance-enhancing abilities.
One, published in 2005 in the International Journal of Sports Medicine, examined 30 male endurance athletes, giving one group high levels of arginine and aspartate (another amino acid), another low levels of both and a third group a placebo. All executed cycling tests. There were no major differences in endurance performance or blood levels of human growth hormone in either of the arginine-aspartate groups.
Another study, published in the Journal of Applied Physiology in 2006, found that oral arginine supplements had no effect on growth hormone levels. Levels were checked in eight men after they took either arginine or a placebo, plus or minus exercise. Although arginine alone did stimulate the release of growth hormone, a greater release was found after exercise alone.
Arginine did prove effective in another study, but only when combined with other dietary amino acids, including branched-chain amino acids and glutamine. The research, published in The Journal of Nutrition, found that elite rugby players who were given the supplement mixture for 90 days showed improvements in their blood's oxygen-carrying capacity.
"People make the leap that if you provide dietary arginine, you're going to get increased synthesis of nitric oxide, says Janet Walberg Rankin, a professor in the department of human nutrition, foods & exercise at Virginia Tech in Blacksburg. "Arginine is a precursor to nitric oxide, but the body has a way to degrade things like this" before it has a chance to use it.
"I don't think it will help athletes at all," Green says. He adds that supplements can help if someone has a deficiency in the diet, but he's never seen someone with an arginine deficiency. "People want easy solutions, and they don't question who's trying to sell them this. They have dubious claims and dubious benefits."
— Jeannine Stein