Harvard Health Letter

By the way, doctor: Is it okay for me to take L-arginine?

Q. I am 92 and have poor blood circulation and an irregular heartbeat. Is it okay for me to take 500 milligrams of L-arginine a day?

A. L-arginine is an amino acid, one of the building blocks of proteins. It's essential for life, but most of us have enough in our bodies. Sometimes it is given as a supplement, but usually to people recovering from serious burns, battling a major infection, or recovering from severe protein malnutrition. It's also given to patients on peritoneal dialysis, an option for kidney failure patients that uses the peritoneum — the membrane that lines the abdomen — to filter out waste products instead of depending on a machine to filter the blood.

L-arginine produces nitric oxide, a gas that helps relax and widen small blood vessels. Small, preliminary studies have suggested that the nitric oxide from L-arginine supplements might help conditions related to narrow blood vessels and low blood flow, such as angina, erectile dysfunction, heart failure, and peripheral artery disease (the narrowing of the arteries in the legs). So, theoretically, it might be helpful to someone like you. But hints and theories don't add up to proof. Most experts don't recommend routine use of L-arginine.

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