If you eat various types of food containing a lot of fresh vegetables and fruits you don’t need a vitamin or mineral supplement. Some special physical conditions like pregnancy, dieting to treat obesity, babies that are not receiving enough nutrients, etc. require supplements of vitamins and minerals. The vitamins you mention can’t cause overdose or adverse effect because the body can easily excrete what it does not use. Vitamin A and D, however, can overload the body. Too much of these vitamins is not a good thing.