Arginine is an amino acid (a building block of protein), produced in the body and found in many foods—especially those rich in protein, such as dairy products, meats, fish, nuts and soybeans.
Most of the time, we produce or consume all the arginine we need. It serves many purposes in the body, but one of its most important jobs is as a precursor for nitric oxide, which in turn is also vital, particularly to cardiovascular health and the healthy functioning of blood vessels.
Arginine is sold as a dietary supplement, usually in a form called L-arginine, and is found in many formulas claiming to promote heart health.
To clear the fog of claims and counter-claims, here’s a summary of what is known:
• Some preliminary studies have found that arginine supplements can improve the function of blood vessels, enhance coronary blood flow, lower blood pressure and even reduce angina and other symptoms in people with heart and/or vascular disease. It has been used to treat heart failure.
• However, two well-designed studies raised red flags about arginine supplements and the heart. One, conducted by researchers at Stanford University and published in Circulation in 2007, found that arginine supplements did not help people with peripheral arterial disease and may even have made matters worse. “Not useful” was the conclusion. And a study at Johns Hopkins Hospital in 2006 found that arginine supplements given to heart attack patients dramatically increased deaths. The study had to be halted; researchers warned strongly against using arginine for heart attack patients.
• Claims are made that arginine supplements can prevent or treat diabetes, but there’s no convincing evidence for this. Moreover, no evidence supports arginine as a muscle builder or performance enhancer, though it is in countless sports supplements.
• Arginine supplements (often containing other dubious ingredients) are marketed to improve erections and enhance libido, but it’s not known whether enough arginine gets to blood vessels in the penis to make a difference. Indeed, some studies have found little or no improvement, compared to a placebo.
• Arginine supplements have been shown to worsen asthma symptoms and increase lung inflammation.
Bottom line: The benefits of arginine supplements are uncertain, and their long-term safety is unknown. Briefly boosting nitric oxide may not actually benefit people with cardiovascular disease, let alone those hoping to avoid it. Excess nitric oxide could have adverse effects.
If you have heart disease or are at high risk, you should be under a doctor’s supervision; there are proven drugs that can help. Cardioprotective drugs such as statins and ACE inhibitors (for high blood pressure) increase nitric oxide availability.
If you have erectile problems, talk to your doctor. Drugs such as sildenafil (Viagra), which boost nitric oxide, may help. But your problem may not be a shortage of nitric oxide. Emotional factors can contribute to sexual problems.
Originally published January 2010. Updated January 2014.