October 18, 2017
2 min read

Neurodevelopment unaffected by maternal iodine supplementation

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In iodine-deficient pregnant women, supplementation with daily oral iodine did not affect the neurodevelopment of offspring at age 5 to 6 years, according to findings from a randomized controlled trial.

“Controlled trials of iodine supplementation in mildly iodine-deficient pregnant women have shown no clear benefits on maternal or newborn thyroid hormone concentrations,” Sueppong Gowachirapant, PhD, a researcher at the Institute of Nutrition at Mahidol University in Nakhon Pathom, Thailand, and colleagues wrote. “Systematic reviews have concluded that the effects of mild iodine deficiency during pregnancy remain uncertain because no placebo-controlled intervention trial has measured child development.”

Gowachirapant and colleagues analyzed data from 832 pregnant women without thyroid disease living in Bangalore, India (n = 318), and Bangkok (n = 514), recruited between November 2008 and March 2011 at a mean gestational age of 10.7 weeks. The median urinary iodine concentration for the cohort was 131 µg/L, indicating mild iodine deficiency at baseline, according to researchers. Researchers randomly assigned participants to 200 µg oral potassium iodide tablets daily (Merck) or placebo until delivery. Primary outcomes were verbal and performance IQ scores on the Wechsler Preschool and Primary Scale of Intelligence-Third Edition (WPPSI-III) and the global executive composite score from the Behavior Rating Inventory of Executive Function-Preschool Version (BRIEF-P) in offspring at age 5 or 6 years. Apart from some unmasking at age 2 years for an interim analysis, the study was double-blind throughout. Analysis was by intention to treat using mixed-effects models.

During the trial, mean compliance with supplementation was 87%.

At a median 5.4 years, researchers did not observe differences between children in the iodine vs. placebo groups for any neurocognitive scores, nor were between-site differences observed. The prevalence of abnormal WPPSI-III composite scores, defined as a score of less than 85, did not differ between the iodine vs. placebo groups for verbal domain (30% vs. 29%, respectively) or performance IQ domain (19% vs. 16%). Abnormal, full-scale IQ scores also did not differ between the iodine and placebo groups (16% vs. 14%).

Additionally, the mean BRIEF-P global executive composite score was 90.6 in the iodine group and 91.5 in the placebo group, for a difference of –0.9 (95% CI, –6.8 to 5). There were no between-group differences in adverse events during gestation or delivery (24 in the iodine group vs. 28 in the placebo group), according to researchers.

Sarah Bath
Sarah C. Bath

In commentary accompanying the study, Sarah C. Bath, PhD, RD, a lecturer in public health and nutrition at the University of Surrey in Guildford, United Kingdom, noted that there is “still a question mark” over whether a supplement of 150 µg iodine per day in early pregnancy is beneficial to neurodevelopment in offspring in regions with mild iodine deficiency.

“Although the trial provides useful information, it cannot be considered as conclusive evidence that iodine supplementation has no benefit in mildly to moderately deficient pregnant women in terms of offspring neurodevelopment,” Bath wrote. “Increasingly, reports in the scientific literature suggest that prepregnancy iodine status is a crucial factor in interpreting the effects of iodine supplementation on thyroid function and offspring cognition, and this needs to be taken into account in any future trial.” – by Regina Schaffer

Disclosures: The Swiss National Science Foundation, Nestle Foundation, Wageningen University and Research and ETH Zurich funded this study. Bath reports she has received lecture fees from the Dairy Council.