Iodine deficiency in pregnancy associated with poor cognitive development

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1. Women with mild-to-moderate iodine deficiency in their first trimester of pregnancy were more likely to have children in the lowest quartile of verbal and reading IQ tests at ages 8 and 9. 

2. The average woman studied was mild-to-moderately iodine deficient such that even in industrialized nations, iodine deficiency in pregnancy may remain an important public health concern. 

Evidence Rating Level: 2 (Good) 

Study Rundown: Researchers found that iodine deficiency during the first trimester of pregnancy was associated with lower verbal and reading IQ scores in offspring at age 8/9. Moreover, in the UK cohort studied, the average woman was mild-to-moderately iodine deficient according to the WHO criteria for iodine deficiency in pregnancy. The implications of these findings are two-fold: adequate iodine status during early gestation is critical for a child’s cognitive development and iodine deficiency may remain a public health concern, even in industrialized nations.

This study is the first to show an association between iodine status in pregnancy and cognitive outcomes. However, it is limited in its ability to assess certain important confounders, including the iodine status of the child at the time of IQ testing. Prospective, larger scale trials are merited to assess the role of iodine supplementation on child cognition and the degree of iodine deficiency in pregnant women in different populations.

Click here to read this article in The Lancet

Click to read an accompanying editorial in The Lancet

Relevant Reading: Uptodate: Iodine Deficiency Disorders

In-Depth [retrospective cohort study]: Researchers evaluated urinary iodine concentrations (corrected for urine volume with creatinine) in stored first-trimester (<13 weeks gestation) spot-urine samples of women from the UK’s Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. Women with iodine-to-creatinine ratios <150 μg/g were considered iodine deficient, whereas those with ratios >150 μg/g were considered iodine replete. Mothers were matched with offspring and the primary outcome evaluated was child IQ at age 8 years/reading level at age 9. Results were adjusted for socioeconomic, parental, and child-specific confounders.

Women with iodine insufficiency in the first trimester were more likely to have children with scores in the lowest quartile for verbal IQ (OR=1.58, p=0.02), reading accuracy (1.69, p=0.007), and reading comprehension (1.54, p=0.02) than women with sufficient iodine intake. As a whole, the cohort was found to be mild-to-moderately iodine deficient, with a median urinary iodine concentration of 91.1 μg/L. Of the 1040 mother-child pairs studied, 646 (67%) had an iodine-to-creatinine ratio <150 μg/g and 312 (33%) had an iodine-to-creatinine ratio >150 μg/g.

By Maren Shapiro and Leah Hawkins

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