Nitric oxide, or NO, supplements are highly popular among weight trainers. These products are often advertised as ergogenic, or muscle-building, agents that enhance workout performance and results by increasing blood flow to muscles and promoting protein synthesis. However, despite their popularity in the bodybuilding community, there is insufficient evidence to conclude that taking supplements of L-arginine, the active ingredient in most nitric oxide supplements, enhances resistance training efforts or outcomes in healthy people.
Sources and Supplements
Most dietary supplements sold as nitric oxide "boosters" contain as their active ingredient the amino acid L-arginine, which is thought to increase circulating nitric oxide levels in the blood, thereby increasing blood flow to muscles and facilitating the synthesis of protein in muscles. These supplements, typically sold in capsule form, also usually contain additional ingredients besides L-arginine, including other amino acids, niacin and inactive ingredients. The vendor of one popular nitric oxide supplement says taking the product will result in "a dramatic increase in muscle size, power output, load capacity and a perpetually pumped-up physique." L-arginine can also be obtained from dietary sources, including brown rice, gelatin, almonds, walnuts, pecans, sunflower seeds, raisins, chicken, chocolate and several other plant-based foods.
Effects of NO Supplementation
While nitric oxide, as a gas produced by the body, does play a role in delivering blood to muscles and other tissues, there is scant evidence to support claims that taking supplemental L-arginine or other types of nitric oxide supplements increases circulating levels of nitric oxide in the blood enough to enhance exercise performance. A 2010 study published in "The Journal of Nutrition" concluded that taking a popular L-arginine-based nitric oxide supplement did not increase nitric oxide synthesis or muscle blood flow in young men at rest or after resistance exercise. Another 2010 study, conducted at the University of Memphis, examined the effects of a nitric oxide supplement containing the molecule 2-[nitrooxy]thyl 2-amino-3-methylbutanoate. Researchers found that while the supplement caused a small increase in circulating nitric oxide levels, it produced no changes to blood flow in resistance-trained men.
Exercise-Induced NO Adaptations
Taking dietary supplements is not a reliable way to boost the function of nitric oxide in the body for weight training purposes, but the act of weight training itself, if performed regularly, may increase bioavailable nitric oxide stores. A review published in the journal "Clinical and Experimental Pharmacology and Physiology" concluded that regular exercise in healthy adults promotes adaptations in the body's nitric oxide systems that increase NO bioavailability and thereby enhance exercise capacity. Another study, published in the journal "Sports Medicine," concluded that chronic, repetitive bouts of exercise increase the bioactivity, or effects, of NO in the body.
NO Supplement Safety
Taking nitric oxide supplements can be dangerous when taken alongside certain medications or for people with certain health conditions. According to MedlinePlus, you should not take supplements containing L-arginine if you also take medications for high blood pressure or nitrate medications that increase blood flow to the heart, as dangerous interactions may occur. L-arginine has moderate interactions with the erectile dysfunction drug Viagra and supplements containing xylitol. L-arginine may also interact with anticoagulant medications and drugs to control blood sugar, according to Mayo Clinic. People with bleeding disorders should also exercise caution with L-arginine, warns Mayo Clinic. Furthermore, as dietary supplements are not regulated by the U.S. Food and Drug Administration, there is no guarantee that any dietary supplement is safe, effective or even contains the ingredients listed on the label.
References
- GNC.com: Force Factor Nitric Oxide Booster
- Bodybuilding.com: MuscleTech NaNOX9 Hardcore
- "Journal of Strength and Conditioning Research"; Acute Effect of Nitric Oxide Supplements on Blood Nitrate/Nitrate and Hemodynamic Variables in Resistance-Trained Men; R.J. Bloomer; October 2010
- "Journal of Nutrition"; Bolus Arginine Supplementation Affects neither Muscle Blood Flow nor Muscle Protein Synthesis in Young Men at Rest or After Resistance Exercis; J.E. Tang; December 2010
- "Clinical and Experimental Pharmacology and Physiology"; "Nitric Oxide as a Metabolic Regulator During Exercise: Effects of Training in Health and Disease"; B.A. Kingwell; April 2000
- "Sports Medicine"; "Exercise and the Nitric Oxide Vasodilator System"; A. Maiorana; 2003
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