Hello there and thanks for the question!
On this page, I answered an earlier question on enriched and fortified foods that might be good to refer to. One thing you should understand about the vitamins and minerals that are added back or enriched is that they are usually not 100% of the recommended daily amount for each of those minerals and vitamins. For example, a serving of a toasted whole grain oat cereal, which has been enriched, has only 25% of the recommended daily amount for vitamin D when including milk. You would need to eat at least 4 servings in a day of that cereal to get the recommended daily amount.
There are some supplements that can pose a risk of reaching the upper limit for use. Vitamins A, E and D are fat-soluble vitamins which means they are stored in our fat. Since fat is more difficult to get rid of from our body, these vitamins can accumulate in our fat which may lead to some adverse side effects.
The best way, of course, to get these types of vitamins is by eating whole foods. By eating a rainbow of colors everyday, you will definitely get your recommended daily amount of vitamin A and E. You can find vitamin D, which has been fortified, in most milk products.
It sounds as if you are interested in learning to eat healthy. Have you thought about enrolling in EatFresh.org's Mini Course? It is a great way to learn how to eat healthy, get some nutritious and delicious recipes and it's FREE! Why not give it a try?
Hope that helps!