Dose-response curve, essential elements

Every essential element follows a dose-response curve, shown in Figure 1.1, as adapted from reference 2. At lowest dosages the organism does not survive, whereas in deficiency regions the organism exists with less than optimal function. 

Figure 1.1 Dose-response curve for an essential element. (Adapted with permission from Figure 3 of Frieden, E. J. Chem. Ed., 1985, 62(11), 917-923. Copyright 1985, Division of Chemical Education, Inc.)...

The following discussion of heavy metals in infant foods is based on recent developments in trace element research that suggest that some elements presently recognized only as "toxic" may have essential functions in certain animal species and perhaps in man. The data discussed here are not intended to detract from the concern for the safety of infant foods they are meant to complement the concern for safety with the concern for adequacy of intake. Before the identification of selenium as an essential element in 1957 the presence of certain concentations of selenium in infant foods would have given rise to serious concern, had one been able to analyze them accurately, because selenium was known only as a carcinogen. Twenty-five years later, hundreds of thousands of children in China are protected by selenium supplements against an endemic cardiomyopathy, the Keshan disease (Chen et al., 1980). This example alone should alert us to the need for a comprehensive understanding of the action of trace elements, of their proven or inferred requirements and of their total dose-response curve. 

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