Suboptimal Maternal Iodine Intake Is Associated with Impaired Child Neurodevelopment at 3 Years of Age in the Norwegian Mother and Child Cohort Study.

Severe iodine deficiency in pregnancy has major effects on child neurodevelopment, but less is known about the potential consequences of mild-to-moderate deficiency and iodine supplement use. We explored the associations between maternal iodine intake and child neurodevelopment at 3 y of age and the potential impact of maternal intake of iodine from supplements on the same outcomes. This population-based prospective observational study included 48,297 mother-child pairs recruited during pregnancy from 2002 to 2008. Maternal iodine intake was calculated based on a validated food-frequency questionnaire answered during midpregnancy that covered mean intake since the beginning of pregnancy. Associations between iodine intake and maternal-reported child language and motor development and behavior problems were explored by multivariable regression analyses. In 33,047 mother-child pairs, excluding iodine supplement users, maternal iodine intake was associated with child language delay ( = 0.024), externalizing and internalizing behavior problems (both < 0.001), and fine motor skills ( = 0.002) but not gross motor skills or the risk of not walking unaided at 17 mo of age. In 74% of the participants who had an iodine intake <160 μg/d (Estimated Average Requirement), suboptimal iodine intake was estimated to account for ∼5% (95% CI: -5%, 14%) of the cases of language delay, 16% (95% CI: 0%, 21%) of the cases of externalizing behavior problems >1.5 SD, and 16% (95% CI: 10%, 21%) of the cases of internalizing behavior problems >1.5 SD. In 48,297 mother-child pairs, including iodine supplement users, we found no protective effects of supplemental iodine during pregnancy on neurodevelopment. Maternal iodine intake below the Estimated Average Requirement during pregnancy was associated with symptoms of child language delay, behavior problems, and reduced fine motor skills at 3 y of age. The results showed no evidence of a protective effect of iodine supplementation during pregnancy.