Future directions for establishing mineral/trace element requirements.

The amount of an element needed to prevent frank deficiency may not be sufficient to support optimal nutrition, but amounts to support optimal nutrition have not been established. Minerals and trace elements are toxic in excess and the interval between the required and toxic amount of some elements is narrow. Thus, lower and upper limits of an optimal range must be established. Before establishing dietary recommendations to support optimal nutriture for minerals, we need (1) sensitive and reliable methods for assessing status of most elements and (2) a better understanding of the influence of nutrient and non-nutrient components of diets upon requirements. Functions such as immune function, anti-oxidant status, muscle strength, glucose metabolism, and blood clotting can be affected by inadequate or excessive amounts of an element and may be more sensitive than specific status indices. Since such functions are not specific, studies must be designed so that a cause and effect relationship between the mineral and the functional index can be established. Two approaches to mineral status assessment may be both sensitive and specific: (1) tests of metalloenzyme function and (2) tracer studies using stable isotopes of minerals. Not only can stable isotopes be used to follow the metabolic fate of a mineral without exposure to radioactivity, they can be used in conjunction with compartmental modeling to predict kinetics and pool sizes in tissues not accessible in humans.