An association between dyslexia and low concentrations of zinc in sweat has been demonstrated in a study of 26 children aged 6-14 yrs recruited from those attending the Dyslexia Institute, Staines, Middlesex, and the Hornsby Learning Centre, London. They were paired with their non-dyslexic school friends, who were matched for age and sex and had no obvious allergies, illnesses or behavior disorders. Sweat from the skin of the back and hair from the occipitonuchal region were collected for analyses of trace minerals at the Biolab Medical Unit, London W1N3FF (correspondence to Dr. Davies).
Zinc concentrations in sweat of dyslexic children (5.4 umol/1) was 66% that in controls (8.0 umol/1, P=.0001). Higher concentrations of copper, lead and cadmium and no differences in zinc concentrations were found in hair of dyslexics compared with controls. 
COMMENT. Zinc in sweat may be a more useful guide to clinical zinc deficiency than hair or serum concentrations [2 - quoted above). The authors propose that zinc deficiency in parents may possibly predispose to familial dyslexia. Zinc deficiency can be due to nutritional factors, inherited defects in zinc metabolism, and several disease states (Nutrition, Diet and Your Child's Behavior. C C Thomas, Springfield, 1986). The high phytate content of protein and the fiber in certain cereals decrease the availability of zinc in persons who eat primarily cereals and little meat. Alcoholism, malabsorption, kidney disease, and sickle-cell anemia predispose to zinc deficiency. The reported possible association of maternal zinc-deficient diets with developmental defects in fetal brain is of interest in relation to the brain malformations recorded on CT scans of occasional children with dyslexia. 
Hair zinc levels of urban toddlers were lower than rural toddlers, especially in summer and in those with frequent upper respiratory tract infections, in a study from North Rhine-Westphalia, Fed Rep Germany . Environmental and seasonal factors and age, sex and infection affect the variability in zinc hair content in addition to dietary factors. Caution in the interpretation of hair analyses is stressed.