I work for a Naturopathic Doctor and it is important to run any supplements past a professional. She has had no end of people taking a supplement because they saw an ad in a magazine or on TV, without knowing if it is even something they need. Often it is the wrong thing.
I take three supplements each and every day, because I know through blood tests that I am low in them. I have consulted with both my GP and ND to be sure I am taking an appropriate dose.