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.