According to the National Institutes of Health (NIH), nitric oxide is a molecule made in your body that provides key benefits, such as improved blood flow and increased energy. Sounds good right? But NIH also says that it's unlikely you'll get much benefit from nitric oxide supplements.
"We know that nitric oxide has lots of important functions in the body. It is important for muscle function and it helps you burn sugar for energy, but when it comes to supplements, there are more questions than answers," says Donald Ford, MD, a family medicine physician at the Cleveland Clinic, Mayfield Heights, Ohio.
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Who Takes Nitric Oxide Supplements?
NIH explains that you can't take an actual "nitric oxide supplement," but you can take supplements of the amino acids arginine or citrulline. These amino acids convert to nitric oxide in your body, and they are the active ingredients in supplements marketed as nitric oxide-boosting. The U.S. National Library of Medicine explains that amino acids are building blocks that your body uses to build proteins. You use amino acids to make proteins that help your body grow and repair tissues.
Because nitric oxide improves blood flow all throughout the body, Mayo Clinic says that people may also take these supplements to lower blood pressure, reduce angina or improve erectile dysfunction.
NIH notes that people may take nitric oxide supplements to try to increase athletic performance since they've heard that nitric oxide may increase blood flow to muscles, improve endurance and support muscle growth.
Do Nitric Oxide Supplements Work?
According to Mayo Clinic, research suggests that taking arginine may in fact decrease angina, lower blood pressure and improve erectile dysfunction. But caution is warranted: "Prescription erectile dysfunction drugs, like Viagra, use the effects of nitric oxide, and they are effective, but they are not the same as supplements," adds Dr. Ford.
NIH says that there is no strong research that shows taking arginine increases nitric oxide or blood flow, and that the ability of arginine to improve exercise or athletic improvement has little scientific support. NIH also says that research does not provide any strong evidence to support citrulline.
"All the studies on nitric oxide supplements have been small. Positive benefits in a few studies have not been replicated in other studies. As far as the benefits of these supplements, you would have to say that the jury is still out," says Dr. Ford.
What About Side Effects?
NIH says that the safety of citrulline is unknown, and that arginine may be safe at up to 9 grams per day for several days or weeks. Higher doses may cause diarrhea or nausea, and the safety of higher doses for more than three months is unknown. Mayo Clinic adds these warnings for arginine:
- Side effects that may include abdominal pain, bloating, gout, or allergic reactions.
- Worsening of a heart attack.
- Triggering of herpes virus.
- Interactions with medications that include medications for blood thinners, blood pressure, diabetes, diuretics, heart medications, and erectile dysfunction.
An alternative to supplements may be foods high in arginine or citrulline. Arginine is found in high protein foods like fish, red meat, soy, beans and dairy foods, says Mayo Clinic. NIH says arginine is also found in nuts, and that watermelon is the best-known source of citrulline.
Read more: Foods High in L-Arginine
There is little evidence to support this supplement as an athletic performance booster according to NIH. Mayo Clinic says arginine might be effective at lowering blood pressure, but you should not take it if you are on a high blood pressure medication, and that you should talk to your doctor first.
"If you want to take this supplement, be aware that supplements are not regulated and they may have other ingredients that can be harmful," Dr. Ford says. "Check with your doctor before you try supplementing on your own."