“Muscle cramps—in the legs, feet, hands, and everywhere else—are often caused by a severe magnesium deficiency,” says Cramp Defense, a supplement that has 70 milligrams of magnesium per capsule. “Since magnesium is constantly lost, take Cramp Defense every day to build up and maintain an optimal magnesium supply,” it says. Does magnesium work, especially for the cramps that often strike older people in bed? Scott Garrison, associate professor of family medicine at the University of Alberta in Canada, may be the best person to ask. “When I was a family physician, I had a patient who was in hospital being treated for pneumonia, and she was magnesium deficient so we gave her a series of infusions of magnesium,” says Garrison.