Vitamins are organic compounds that are vital for the normal functioning of the body. Each vitamin has different functions and has various effects on general health. While vitamin A has important effects on eye health, vitamin D on bone health, and vitamin C on skin health, all three vitamins also play a very important role on the immune system. The body's vitamin needs may vary from person to person. In addition to looking at the vitamin levels in the blood when determining the body's vitamin needs, we also examine the enzymes involved in the digestion, absorption and activation of these vitamins; It is necessary to take into account the status of the genes that encode the proteins that carry the vitamins taken into circulation in the blood and the receptors to which the vitamins bind for their cellular functions. In this way, it is possible to use healthier and harmless vitamin supplements with a personalized approach.