Abstract
Responses to essential micronutrient deficiencies fall into two categories. A Type I nutrient deficiency leads to depletion of body stores and then to a reduction in those metabolic functions dependent on the nutrient. A Type II deficiency, because there are no stores other than normal tissue, evokes preservation of plasma and tissue levels, even at the expense of growth, repair and immune function. Catabolism of normal tissue to release depleted nutrients can lead to deficits of many or all Type II nutrients. Treatment requires balanced supplementation of all these, not only of the limiting nutrient. Animal and human studies demonstrate the need for different approaches to the two types of deficiency.