Introduction

A trace element, by definition, contributes less than 0.01% to the total body weight. It is a term that, by common usage, applies to those elements that are consistently present in human tissues and have one or more definite, probable, or possible physiologic roles. The total body content of trace elements is small, but concentrations in individual tissues can range up to many parts per thousand. For example, the high iron concentration in erythrocytes results frequently, but mistakenly, in categorizing it as a major mineral. Trace elements that have a known or probable/possible role in human nutrition are listed in Table 17.1. This list may vary a little according to the author, reflecting the extent of current uncertainty, and it may not yet be complete. Since the publication of the last edition of this book, there has been progress, in some instances remarkable progress, in our understanding of the biology and clinical importance of those minerals that had already attracted clinical interest, while relatively little or no progress has been made with those of marginal or uncertain clinical relevance. Iron, zinc, and iodine and, to a lesser extent at this time, selenium and copper are the minerals that merit most attention in this chapter.

Though the trace elements are present in the human body in such small quantities, they are analogous to their organic counterparts, the vitamins, in that they have multiple, indispensable roles in a variety of important metabolic pathways.