Nitric oxide supplements are hot in the bodybuilding supplement world. Most are based on the amino acid arginine, which is the immediate precursor of nitric oxide synthesis in the body. How much arginine converts to NO depends on several factors, including enzyme activity. Another factor is how much arginine gets absorbed into the body. Taking large doses of oral arginine increases the activity of an enzyme in the liver called arginase, which breaks down arginine, thus blunting it’s uptake into the blood.
Some studies show that you need 18 grams or more for arginine to be effectively converted into NO. In contrast most NO supplements contain a modest dose of three to four grams. The larger doses of arginine require intravenous infusion to bypass the arginase barrier in the liver. Attempting to swallow 12 grams of arginine or more at a time usually results in nausea. That’s probably why most NO supplements contain smaller doses.
Several studies have shown that some bodybuilders who’ve used NO supplements experience symptoms indicating excess NO production in the body. One typical side effect is a drop in blood pressure, since NO widens, or dilates, blood vessels. Though it may not be welcome, it does show that the NO supplements are working as advertised. Other studies, however, show that no oral dose of arginine has any effect on blood vessels. As researcher Richard Bloomer, Ph.D., has pointed out, you wouldn’t want a huge sudden release of NO. Excess amounts are implicated in septic shock—sometimes called blood poisoning—which has a 50 percent mortality rate. Keep in mind that NO is a double-edged biochemical sword. It’s a free radical, which, when combined with hydrogen peroxide released during normal metabolism, becomes peroxinitrate, one of the more potent and damaging free radicals.
NO offers vital benefits besides the well-known expansion of blood vessels. Studies show that NO generation in the heart is involved in important cell-signaling reactions. In the brain NO regulates transmissions across neurons. It’s also involved in release of hormones, including both testosterone and growth hormone. Various diseases have a characteristic NO deficiency—for example diabetes, high blood pressure and pulmonary hypertension.
The most popular method for increasing NO is through the use of Viagra, which lowers blood pressure. Diabetics, who often lack NO, don’t respond as well to Viagra. Nitric oxide combined with vitamin B12 is proving effective for treating dogs that have cancer. The B12 disguises the NO, enabling it to penetrate and destroy tumors through its free-radical action.
Arginine is not the only means of boosting NO synthesis. Another type of supplement combines L-carnitine with propionate, a salt compound, and the amino acid glycine. Taking 4.5 grams of it daily boosts NO by an average of 18 percent. Taking antioxidants also protects against the premature breakdown of NO in the blood.
Perhaps the most overlooked method of boosting NO is also the cheapest and most available—eating vegetables. Why would vegetables boost NO synthesis? They naturally contain nitrate and nitrites, which are the end products of NO metabolism. While they’re usually inert, the body can recycle them into active NO. The best nitrate-rich foods include lettuce, spinach, beetroot and pomegranate. Another option is to drink vegetable juices. Those foods supply a sustained-release alternative to taking large doses of arginine and may prove helpful to those who have defects in the enzymes that convert arginine into NO.
Butler, A.R.,et al. (2008). Therapeutic uses of inorganic nitrite and nitrate: From the past to the future. Circulation. 117:2151-2159.