THE VITAMIN D RIDDLE I take a vitamin D supplement every day—800 international units (IU). Why? Because it’s what I’ve been hearing for years that a senior should be taking. Until now, I didn’t much question this beyond doing some research for my post Dietary Supplements—Do They Work? last February. Vitamin D is necessary for building strong bones. Your body can only absorb calcium, the main component of bone, when this vitamin is present. Your body forms vitamin D naturally after exposure to direct sunlight; When ultraviolet (UV) rays hit your skin it triggers production of a chemical in your...