While severe iodine deficiency of the pregnant mother imposes well-documented impairment of mental development and function of her offspring, the effect of mild iodine deficiency in cognitive function is less-studied...until now. A study from Erasmus University in The Netherlands found that children born of pregnant women consuming 49-136 µg iodine/creatinine showed significant effects in inhibition and working memory. The study was published The Journal of Nutrition jn.nutrition.org/content/early/2012/10/16/jn.112.161950.abstract.

A strength of our study is that we examined the relationship between mild iodine deficiency during early pregnancy and executive functioning in children at 4 y of age, thereby including maternal nutrition and thyroid function as determinants of the same pathway. In addition, the large population-based prospective cohort enabled us to control for important confounding factors, including lifestyle factors, socioeconomic factors, and known determinants of fetal and infant development. However, this does not completely exclude residual confounding. Because data were more complete in more highly educated mothers, we cannot rule out that selective nonresponse influenced our findings.

The effect sizes in our study were rather small because executive functions were measured instead of clinical diagnosis of behavioral problems. Nevertheless, the continuous traits of executive functioning provide better statistical power because exposure and outcome are rare. More importantly, the BRIEF-P scale converges with a variety of clinical groups including traumatic brain injury, autism spectrum disorders (60), ADHD, and Tourette syndrome (61).

In conclusion, low maternal urinary iodine status during early pregnancy is associated with impairment of executive functioning in children at 4 y of age.