Micronutrient supplementation is considered as a useful intervention in many cases. Zinc is one of these micronutrients and an essential cofactor for over 100 enzymes, both metalloenzymes and metal-enzyme complexes that are required in the metabolism of carbohydrates, fatty acids, proteins and nucleic acids. Zinc is considered as an essential element in neuronal development, synaptogenesis and synaptic transmission.
In experimental animal studies, zinc deficiency during early brain development is mainly related with malformations. In humans, neuropsychological and neurobehavioral effects of zinc deficiency are largely studied in severely zinc deficient groups or cases exposed to deficiency during early developmental stages. In addition zinc supplementation studies mainly occur in the gestational period or infancy and use zinc doses higher than the protective dosage. Limited numbers of interventional trials have been performed to demonstrate the effects of zinc supplementation on behavioral, cognitive and neuropsychological functioning in school-aged children. Some of these studies showed no significant effects on average attention span and short-term memory. On the other hand some found improvement in neuropsychological performance and decrease in the number of children with clinically significant parents' scores for attention deficit and hyperactivity. When searched for internalizing symptoms, no significant effect was revealed in parent-teacher rated scales.
In clinical cases with attention deficit hyperactivity disorder (ADHD) and autism low serum zinc levels were reported. Zinc supplementation studies in ADHD cases showed significant improvement reported in parents' and teachers' ratings of hyperactivity, impulsivity and socialization scores. Furthermore, one study found that improvement was mainly in parent-teacher-rated inattentive symptoms in ADHD cases. In a placebo controlled study, zinc supplementation in addition to ADHD treatment revealed a 37% reduction in d-amphetamine dose compared to placebo, though no significant superiority of zinc supplementation for ADHD symptoms was observed.
In conclusion, zinc supplementation studies suggest a special relationship to ADHD diagnosis. However it is not possible to establish either an etiological relation or an alternative treatment approach in ADHD.