Vitamins

The vitamins are a disparate group of organic compounds that are required in small amounts (mg or µg per day) for the maintenance of normal health and metabolic integrity. Four vitamins (A, D, E, and K) are lipid soluble, while the others are water-soluble. Determining how much of any particular vitamin is required for health is not straightforward, a standard technique being to deprive volunteers of the vitamin in question until there is detectable metabolic change and then replete with graded doses of the vitamin until normal metabolism is restored, with the reference intake (recommended daily intake or amount or recommended dietary allowance) set at 2× standard deviation above the average requirement.