Abstract
BackgroundAdverse effects of severe maternal iodine deficiency in pregnancy on fetal brain development are well-established, but the effects of milder deficiency are uncertain. Most studies examine iodine status in pregnancy; less is known about iodine nutrition before conception. ObjectiveWe examined relations between maternal preconception iodine status and offspring cognitive function, within a prospective mother-offspring cohort. MethodsMaternal iodine status was assessed through the use of the ratio of iodine:creatinine concentrations (I/Cr) in spot urine samples [median (IQR) period before conception 3.3 y (2.2–4.7 y)]. Childhood cognitive function was assessed at age 6–7 y. Full-scale IQ was assessed via the Wechsler Abbreviated Scale of Intelligence, and executive function through the use of tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Analyses (n = 654 mother-child dyads) were adjusted for potential confounders including maternal intelligence, education, and breastfeeding duration. ResultsThe median (IQR) urinary iodine concentration was 108.4 µg/L (62.2–167.8 µg/L) and the I/Cr ratio 114 µg/g (76–164 µg/g). The preconception I/Cr ratio was positively associated with child IQ, before and after adjustment for potential confounding influences [β = 0.13 (95% CI: 0.04, 0.21)/SD, P = 0.003]. 8.9% of women had a preconception urinary I/Cr ratio <50 µg/g; compared with those with an I/Cr ratio ≥150 µg/g, the IQ of their offspring was 0.49 (95% CI: 0.79, 0.18) SD lower. There were no associations with the executive function outcomes assessed via CANTAB, before or after adjustment for confounders. ConclusionsThe positive association between iodine status before conception and child IQ provides some support for demonstrated links between low maternal iodine status in pregnancy and poorer cognitive function reported in other studies. However, given the negative effects on school performance previously observed in children born to iodine-deficient mothers, the lack of associations with measures of executive function in the present study was unexpected. Further data are needed to establish the public health importance of low preconception iodine status.
Highlights
Iodine is an essential nutrient, required for the synthesis of thyroid hormones, which are known to be critical for cellular metabolism, growth, psychomotor and physical development, and function at all stages of life [1]
The characteristics of 654 mothers and children in the subsample of Southampton Women’s Survey (SWS) for whom preconception maternal iodine status and cognitive function data were available are shown in Table 1, together with data for the remaining SWS mothers and children who were not included in the analyses
There were some differences when women in the subsample were compared with the rest of the cohort: they had slightly lower iodine intakes, were less likely to smoke in pregnancy, and more likely to have breastfed for longer
Summary
Iodine is an essential nutrient, required for the synthesis of thyroid hormones, which are known to be critical for cellular metabolism, growth, psychomotor and physical development, and function at all stages of life [1]. There is a growing body of evidence that links milder forms of thyroid dysfunction to adverse pregnancy outcomes [4], suggesting that there may be important effects of mild or moderate maternal iodine deficiency on fetal development. Adverse effects of severe maternal iodine deficiency in pregnancy on fetal brain development are wellestablished, but the effects of milder deficiency are uncertain. Objective: We examined relations between maternal preconception iodine status and offspring cognitive function, within a prospective mother-offspring cohort. Methods: Maternal iodine status was assessed through the use of the ratio of iodine:creatinine concentrations (I/Cr) in spot urine samples [median (IQR) period before conception 3.3 y (2.2–4.7 y)]. Conclusions: The positive association between iodine status before conception and child IQ provides some support for demonstrated links between low maternal iodine status in pregnancy and poorer cognitive function reported in other studies.
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