Iodine Deficiency and Infant and Child Cognitive Development: A Review of the Evidence and Some Baseline Findings

Iodine deficiency is an important cause of impaired infant and child development around the world. We searched for trials and observational studies where iodine supplements were provided in any form to women of reproductive age, pregnant women, infants or children and which reported on infant or child cognitive outcomes. We identified 27 studies in total; 9 randomized placebo-controlled trials (RCT) and 16 other designs including non-randomized controlled trials and observational studies which compared supplementation vs. placebo/no intervention, timing of supplementation, or both. Studies in which children 6 to 12 years were randomized to receive an iodine capsules tend to show mixed cognitive outcomes, where 25% showed an advantage for those receiving iodine. No randomized trials were available for children under 6 years; despite confounds, the general finding is an advantage for those who themselves or their mothers received iodine.  Overall, positive results were seen most often in non-verbal domains of cognitive functioning (e.g. reasoning).  Ethiopia lacks natural sources of iodine. Consequently, recent research on Ethiopian children aged 6 to 12 years has yielded high rates of goiter and low levels of urinary iodine.  To examine levels of iodine deficiency and cognitive development in children under 6 years, we collected data from a representative sample of children 8, 20, and 60 months of age in the Amhara region of Ethiopia.  Cognitive measures included the Bayley Scales of Infant and Toddler Development for the 8- and 20-month-olds, and verbal and non-verbal reasoning along with school readiness measures for 60-month-olds. Nutritional indicators included iodine and iron sufficiency, weight, height and diet.  Findings provide insight into how iodine deficiency affects the cognitive development of children in relation to contextual variables such as parental education, home stimulation, and overall nutrition.