My original karate sensei, also a certified nutritionist, said that the one thing that vitamins are certain to do is to increase the dollar value of your urine.
One problem with "multi" vitamins is that they usually contain iron, and the (male) body has no way to get rid of it. Modern diets are quite rich and most of us probably get far more iron than we need anyway. I donate a pint of blood several times a year, and eliminating excess iron is a significant part of the reason.