If something is either essential or good for the health, surely more of it must be good for you? Such at any rate is the reasoning of half the American population who, between them spend more than $30 billion on dietary supplements, that is to say $200 a head per annum. All things considered, these supplements must be pretty safe, unlike prescription drugs, for few people die or have serious side-effects from them. Whether they do any good, other than as placebos, is another question entirely of course.According to an article in a recent edition of the New England...