There is a lot of scientific research that shows that a balanced diet is all that is required to provide all the vitamins the body requires and that supplements at best are a waste of money and at worst in large doses can cause harm.

The only exception would be for people that have specific conditions that a doctor suggests supplements for.

Edit: I though i would add one example i read recently about Omega 3 that really stands out: http://www.newscientist.com/article/mg20627601.400-omega3-fi...