Vitamins are organic substances, needed in small amounts, that are essential for processes that occur in the human body. Essential means that we cannot manufacture these substances at all or in amounts necessary to sustain normal health and life. We must acquire these substances from our diet or other outside source (usually supplementation if diet falls short). The functions affected by a particular vitamin will be impaired in a deficiency state (chronic lack of the nutrient) and can lead to predictable health consequences and ultimately death in severe instances (which is very rare).