Vitamin Requirements and Reference Intakes

A priori, it would appear to be a simple matter to determine requirements for vitcunins. In practice, a number of problems arise. The first of these is the definition of the word requirement. The U.S. usage (Institute of Medicine, 1997) is that the requirement is the lowest intake that will maintain a defined level of nutriture in an individual - i.e., the lowest amount that will meet a specified criterion of adequacy. The WHO (1996) defines both a basal requirement (the level of intake required to prevent pathologically relevant and clinically detectable signs of deficiency) and a normative requirement (the level of intake to mainttiin a desirable body reserve of tbe nutrient). 

We bave to define tbe purpose for which we tue determining the requirement (the criteria of adequacy), then determine the inttike required to meet these criteria. 

1 Criteria of Vitamin Adequacy and the Stages of Development of Deficiency 

For my nutrient, there is a range of inttikes between that which is clearly inadequate, leading to clinical deficiency diseeise, and that which is so much in excess of the body s metabolic capacity that there may be signs of toxicity. Between these two extremes is a level of inttike that is adequate for normed health md the maintenmce of metabolic integrity, md a series of more precisely definable levels of intake that are adequate to meet specific criteria md may be used to determine requirements md appropriate levels of inttike. These follow. 

Clinictd deficiency disease, with cleeu anatomictd and functiontd lesions, and severe metabolic disturbmces, possibly proving fatal. Prevention of deficiency disease is a minimtd goal in determining requirements and is the criterion of the WHO basal requirement (WHO, 1996). 

---