Anything that seems too good to be true almost always is. It’s hard for me to believe that taking anything can cure or prevent a huge number of conditions.

That’s why I have kept changing my mind about arginine (also known as L-arginine). I have known about its powers for years. In 1998 a leading endocrinologist, Dr. Joe Prendergast, brought it to my attention for its ability to reverse the most common complication of diabetes, heart disease.

Arginine is one of the 20 amino acids that make...