RDA-A minimum amount of each vitamin is needed in order for the biochemical systems of the body to function both correctly and efficiently. To simplify dose of each vitamin, we have come up with the term, recommended daily allowance (RDA). The recommended daily allowance of a vitamin, is an amount of a particular vitamin needed on a daily basis to function normally. We must not forget that each RDA for a particular vitamin is based on averages in the population. These are not always correct for each individual, but can be tailored accordingly. The RDA is only a guideline, and with good intentions. The RDA keeps things simple, assuming that we are not all well-versed in the sciences behind more accurate calculation of need. But as we learn, we shall see that RDA can vary considerably depending on body weight, sex (male, female), metabolism, lifestyle, genetics, and disease states. Strong variations in these variables can cause deficiencies leading to disease as will cover.