There are 2 major types of vitamines: B vitamines and C are hydrosoluble and the other type are liposoluble (A, E, D, K). The liposoluble vit. need fat to be absorbed and can be toxic because they acumulate in fat tissue.
diet with organic foods (not preocessed) is also of max importance with supplementation of natural sources extracted vitamins, i found black rice mixed with vegetables very very rich in nutritional antioxidants/vitamins
it is not the vitamins dose we need to take but the serum levels we need to achieve.the dose must be personalized according to deficency, this is to achieve the best of possible results
some vitamins like liposoluble can be taken without checking levels like for example vit b complex, vit c, glutathione and vit E
http://www.lef.org/news/LefDailyNews.htm?NewsID=13380&Section=VITAMINS