Many bodybuilders swear by nitric oxide supplements, crediting them for increased vascularity, better post-workout "pump" and quicker recovery time. Though bodybuilding benefits are largely unproven, these supplements may be beneficial for certain populations. Because there are pros and cons of using nitric oxide supplements, seek a physician's guidance before taking.
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Most nitric oxide supplements are made from L-arginine, an amino acid that helps build nitric oxide, or NO, levels in the blood. A 1994 study in the journal "Clinical and Experimental Immunology" found that HIV-positive patients in whom a positive nitrogen balance had been induced demonstrated normal NO synthesis, while severely underweight patients showed low levels of NO synthesis. This demonstrates nitric oxide's connection to weight maintenance. MedlinePlus characterizes L-arginine as "possibly effective" for inducing weight gain in HIV and AIDS patients when combined with glutamine and hydroxymethylbutyrate. It is unknown as of time of publication if the weight-gain benefits extend to healthy people as well.
MedlinePlus notes that the evidence is weak regarding athletic enhancements attributed to NO supplements. MayoClinic.com acknowledges that there is scant evidence showing that it may improve blood flow, but the data regarding it's usefulness to athletes is conflicting and more research is needed before it can be conclusively recommended or discounted. If nitric oxide does increase blood flow, that would account for the "pumped" look following a workout, but the extra definition is not permanent and will subside. Additionally, nitric oxide supplements have never been shown to reduce or delay fatigue.
Effects on Other Conditions
Although it may not necessarily be a benefit to athletes, nitric oxide may play a role in treating certain medical conditions. The basic ingredient L-arginine may be an effective adjunct to surgery recovery and treatment for heart failure and artery disease. According to MedlinePlus, it shows promise as a treatment for erectile dysfunction because of the possibility of improved blood flow. MayoClinic.com notes that it is commonly used to test growth hormone levels, and can be an effective part of treatment for inborn errors of urea synthesis.
May Be Risky
Because nitric oxide supplements are made from amino acids, they are relatively safe when used as directed short-term. But MedlinePlus says they may exacerbate herpes symptoms, lower blood pressure and increase your risk of death after a heart attack. These supplements interact negatively with nitrates and blood pressure medication, and may also interact with erectile dysfunction medication. Possible side effects include digestive discomfort, diarrhea, bloating, nausea, lower back pain, leg restlessness and changes in blood sugar. Consult your doctor before use, especially if you have a medical condition or are taking medication.