More vitamin doesn't mean better health. Water soluble vitamins saturate in your body, and the excess is excreted in urine. Fat soluble vitamins, however, build up, and taking more than you need may lead to various kinds of poisoning (particularly A, D, B3 and B6 [3]).
Generally speaking if you're not eating 100% of your meals at McDonalds, you're getting all the vitamins you need from your diet and more vitamins is at best neutral and at absolute worst fatal.
Here's a study from 2011 that shows no decrease in all cause mortality, no decrease in cancer risk [1]. Here's one that shows all cause mortality was 5% higher in multivitamin takers [2].
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3105257/