This article is from the Food Science FAQ, firstname.lastname@example.org (Paul E. J. King) with numerous contributions by others.
A balanced and varied diet -- not too much of anything -- will
normally supply enough from a nutrition point of view. There may be
problems for children, adolescents, the elderly, women during
pregnancy and lactation, and people on slimming diets. These people
would probably benefit from a vitamin and mineral supplement. There
is also increasing evidence that certain vitamins (i.e. vitamins C
and E) have additional beneficial properties as antioxidants.