Trace Elements in Infancy: A Supply/Demand Perspective

Abstract

The rapidly growing newborn is particularly vulnerable to imbalances in nutrient supply. In early life, milk or infant formula will be the sole diet for long periods of time, putting strong demands on the particular diet to provide adequate but not excessive quantities of each nutrient. Later in life, the variety of the diet, as well as better homeostatic regulation, diminish this risk. While we know the protein and energy requirements of infants reasonably well, our knowledge regarding the micronutrients is more limited. This is particularly evident for the trace elements, which are present in milk in comparatively low concentrations (1). For this reason, infant formulas intended to replace human milk are supplemented with trace elements, with the possibility of excesses to occur (2). Thus, both deficiency and toxicity of trace elements may occur during infancy (3). This situation is further complicated by the interactions that occur among trace elements, i.e., while a need for supplementation with one trace element is recognized, the possibility of this element reducing the absorption of another element is less commonly taken into account. This is illustrated by the fact that the Committee on Nutrition of the American Academy of Pediatrics have established minima for the level of several trace elements in formulas, while a maximum has only been recommended for iron (4). On the other hand, it is difficult to issue strong recommendations before an incidence of trace element deficiency or toxicity is documented. This is a difficult task since there are established clinical tools to detect only iron deficiency. Zinc, copper, manganese and selenium status are much more difficult to assess and blood or serum levels are not tested as a clinical routine. Further compounding the lack of tests is the vague nature of symptoms of trace element deficiency/toxicity in their less pronounced forms. General failure to thrive and possibly slower than normal growth are known consequences of trace element deficiency in human infants, but are too nonspecific to trigger a suspicion of trace element deficiency. While the mentioned signs may not be of serious concern, the recent findings of marginal trace element deficiency causing impairment in immune competence (5), in turn leading to a higher risk for infection, should be of concern.