Micronutrient intake and psychological performance of schoolchildren: consideration of the value of calculated nutrient intakes for the assessment of micronutrient status in children.

Although the grosser clinical manifestations of micronutrient deficiency are now rare in Western society, biochemical and functional disturbances may occur before the onset of overt deficiency states. It has been argued that, since the vast majority of subjects with apparent biochemical abnormalities do not progress to classical, overt deficiency states, these abnormalities are relatively unimportant. However, such arguments take little account of evidence linking sub-optimal intakes of several micronutrients to increased susceptibility to chronic disease; nor do they allow for the potential positive benefits for well-being and improved quality of life which are likely to be associated with optimal body function. Recently, there has been considerable speculation about the role of marginal micronutrient deficiency in relation to optimal cognitive function in children and adolescents following the publication of four studies reporting a significant improvement in non-verbal IQ after a period of micronutrient supplementation (Benton & Roberts, 1988; Benton & Buts, 1990; Schoenthaler et al. 1991a,b). The implication of these studies is that a proportion of the subjects were not receiving a sufficient dietary supply of one or more of the micronutrients provided by the supplement, and that the correction of these dietary deficiencies resulted in improved performance in tests of intelligence. There are numerous papers in the literature implicating vitamin and mineral deficiencies in abnormal brain development and learning ability and, although the mechanisms responsible for these impairments are poorly understood, there is no doubt that micronutrients are essential for our mental well-being (Southon, 1990). However, where studies relating diet to cognitive performance do not present adequate information on the diet and nutritional status of subjects, the development of hypotheses is limited. In those studies where dietary assessment has been performed, conclusions about dietary adequacy are based on intake values calculated from tables of food composition. The present paper considers the value of food table data for estimating micronutrient intake and micronutrient status in young, growing individuals. It presents our own data from a group of 13-14-year-old volunteers, since a search of the literature revealed no study which combined dietary assessment, from both food table calculations and direct analysis of the diet, with a range of biochemical indices of micronutrient status. Dietary intake was measured using a 7 d weighed intake method and direct analysis of duplicate diets. Micronutrient status was assessed via a range of biochemical analyses performed on fasting blood samples.