Urinary iodine levels during pregnancy are associated with alterations in executive function in children

Low maternal urinary iodine status during pregnancy is related to impairment of executive functioning in children at 4 years of age but it could not be explained by low intake or maternal thyroid function. The observed impairments in executive function at an early age are considered to be subclinical symptoms so further studies are needed.

Iodine is critical for the synthesis of thyroid hormones, fatal and early postnatal growth and development of most organs, especially of the brain. During pregnancy, the production of thyroxin physiologically increases by 50%, so the need has to compensated with a 50% increases in daily iodine requirement. However, girls and women of reproductive age usually have deficient iodine consumption. During pregnancy, there is a severe iodine deficiency, which affects maternal thyroid function and child neurobehavioral development. However, it remains unclear whether mild-to-moderate iodine deficiency during pregnancy detrimentally affects maternal thyroid function and neurodevelopment in offspring. The aim of this study was to examine the association between maternal urinary iodine during early pregnancy and executive functioning in children at 4 years of age. Moreover, the modification of this association was investigated by maternal diet and thyroid function.

In this population-based cohort, 1156 women were chosen. During pregnancy, thyroid hormone concentrations and urinary iodine was measured. In 692 of their children, impairment of executive functioning was assessed by the Behaviour Rating Inventory of Executive Function. 500 mothers of Dutch national origin completed an FFQ. Analyses were performed by using regression models. Mothers with low levels of iodine in their urine during early pregnancy had 4 year-old children who scored significantly higher on the problem scales of inhibition [β = 0.05 (95% CI: 0.01, 0.10), P = 0.03] and working memory [β = 0.07 (95% CI: 0.02, 0.12), P = 0.003] than pre-schoolers born to mothers who had high urinary iodine. Although maternal dietary intake and thyroid hormone concentration did not significantly modify these associations, the associations between urinary iodine and problems of inhibition were attenuated after adjustment for maternal psychological symptoms. Moreover, consuming bread [β = 0.61 (95% CI: 0.27, 0.95), P < 0.001] and eggs [β = 1.87 (95% CI: 0.13, 3.62), P = 0.04] resulted in higher urinary iodine.

In conclusion, low maternal urinary iodine status during pregnancy is related to impairment of executive functioning in children at 4 years of age. However, it could not be explained by low intake or maternal thyroid function. The observed impairments in executive function at an early age are considered to be subclinical symptoms so further studies are needed.

References

  1. van Mil, N.H., et al., Low urinary iodine excretion during early pregnancy is associated with alterations in executive functioning in children. J Nutr, 2012. 142(12): p. 2167-74.