What you should know about: Magnesium

Many Americans take magnesium supplements, which are sometimes marketed as super pills that help a long list of ailments including muscle tension, low energy, and trouble sleeping. But think twice before you reach for this mineral in pill form. "The main reason to take this is a documented low body magnesium, usually identified by a low blood level," says Dr. Bruce Bistrian, chief of clinical nutrition at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School.