Yes, multi vitamins do work. You are taking Centrum though, which is not the best. This is just a very basic brand that absorbs semi well. Try this experiment...drop you vitamin into a glass of vinegar and watch how it dissolves. Vinegar is close to the same PH as the stomach.
The best is to take a 3 a day vitamin complex. This is due to the fact that even with a good vitamin, you don't absorb all you need in one pill. With a 3 a day you can take a vitamin with every meal. This increases your body's absorbency to 65% instead of 15%.
Excellent vitamin complex above.