Abstract
There is increasing evidence that even mild gestational iodine deficiency (GID) results in adverse neurocognitive impacts on offspring. It’s unclear, however, if these persist long-term and whether they can be ameliorated by iodine sufficiency in childhood. We followed a unique cohort (Gestational Iodine Cohort, n = 266) where gestation occurred during a period of mild population iodine deficiency, with children subsequently growing-up in an iodine replete environment. We investigated whether associations between mild GID and reductions in literacy outcomes, observed at age 9-years, persisted into adolescence. Comparisons were made between offspring of mothers with gestational urinary iodine concentrations (UICs) ≥ 150 μg/L and < 150 μg/L. Educational outcomes were measured using Australian National Assessment Program—Literacy and Numeracy (NAPLAN) tests. Children whose mothers had UICs < 150 μg/L exhibited persistent reductions in spelling from Year 3 (10%, −41.4 points (95% Confidence Interval −65.1 to −17.6, p = 0.001)) to Year 9 (5.6%, −31.6 (−57.0 to −6.2, p = 0.015)) compared to children whose mothers had UICs ≥ 150 μg/L. Associations remained after adjustment for biological factors, socioeconomic status and adolescent UIC. Results support the hypothesis that mild GID may impact working memory and auditory processing speed. The findings have important public health implications for management of iodine nutrition in pregnancy.
Highlights
Insufficient iodine during gestation, in the first trimester, is a major cause of preventable neurological damage [1,2]
From the original Gestational Iodine Cohort, 266 singleton offspring were successfully linked to National Assessment Program—Literacy and Numeracy (NAPLAN) data
We demonstrate that some associations between mild gestational iodine deficiency (GID) and literacy outcomes observed at age 9-years [4] persist into adolescence, despite the children having completed more than ten years of formal education and having grown up in an iodine replete environment
Summary
Insufficient iodine during gestation, in the first trimester, is a major cause of preventable neurological damage [1,2]. In 2013, two landmark observational studies highlighted the consequences of mild gestational iodine deficiency (GID). Reported that 9-year-old Australian children had reduced educational performance in literacy, but not numeracy, assessments if their mothers had urinary iodine concentrations (UICs) < 150 μg/L during pregnancy compared to children whose mothers had UICs ≥ 150 μg/L [4]. Subsequent studies support these findings: Moleti et al [5] described defective cognitive function, verbal abilities, in Italian children (aged 6–12 years) whose mothers had mild GID and;
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