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Lifestyle and Environment · Nutrition and Metabolic Health

Association of Maternal Iodine Status With Child IQ: A Meta-Analysis of Individual Participant Data

Levie D, Korevaar TIM, Bath SC, Murcia M, Dineva M, Llop S, Espada M, van Herwaarden AE, de Rijke YB, Ibarluzea JM, Sunyer J, Tiemeier H, Rayman MP, Guxens M, Peeters RP

Published December 2019 The Journal of clinical endocrinology and metabolism
DOI 10.1210/jc.2018-02559 PMID 30920622 PMC PMC6804415

RRM Academy Synopsis

Lower iodine in early pregnancy was linked to lower child verbal IQ

A meta-analysis of 6180 mother-child pairs found that lower iodine status up to week 14 of pregnancy was linked to lower verbal IQ in children. The pairs came from three birth cohorts, and the analysis pooled their individual records. The link with verbal IQ was absent for iodine measured after week 14. Nonverbal IQ showed no statistically significant link.

Key Findings

  • Pooling all three cohorts, a higher urinary iodine/creatinine ratio went with a higher mean verbal IQ along a positive curvilinear line. The pooled association with nonverbal IQ was not statistically significant.
  • Verbal IQ in children of women with a deficiency-range ratio did not differ significantly from the sufficient range (−0.6 point; 95% CI: −1.3 to 0.1 points; P = 0.082).
  • Nonverbal IQ in children of women with a deficiency-range ratio did not differ significantly from the sufficient range (−0.6 point; 95% CI: −1.7 to 0.4 points; P = 0.246).
  • The verbal IQ association had an overall effect of ∼5 IQ points in the first 12 weeks and ∼3 IQ points in weeks 12 to 14. It was absent after week 14.

Interpretation

The study pooled the original records of mother-child pairs from three prospective birth cohorts. The cohorts ranged from adequate iodine status in the Dutch group to moderate deficiency in the British group. IQ was assessed between ages 1.5 and 8 years. The study excluded women with preexisting thyroid disease, multiple pregnancies, or fertility treatment. It also excluded women on drugs that affect the thyroid. Verbal IQ showed a possible interaction with week of pregnancy (P for interaction = 0.078), so the authors split the analysis by week. The authors note that one urine sample may not reflect a woman's overall iodine status.

RRM Context

RRM views health before conception and in early pregnancy as one picture. Nutrition and thyroid health belong to it. The authors suggest that iodine stores before conception may be critical, because early in pregnancy the fetus depends on thyroid hormone from its mother. Cycle charting tracks ovulation, so conception and the early weeks this study examines can be dated.

Our editorial summary of this paper, not the article's abstract.

Abstract

Context

Although the consequences of severe iodine deficiency are beyond doubt, the effects of mild to moderate iodine deficiency in pregnancy on child neurodevelopment are less well established.

Objective

To study the association between maternal iodine status during pregnancy and child IQ and identify vulnerable time windows of exposure to suboptimal iodine availability.

Design

Meta-analysis of individual participant data from three prospective population-based birth cohorts: Generation R (Netherlands), INMA (Spain), and ALSPAC (United Kingdom); pregnant women were enrolled between 2002 and 2006, 2003 and 2008, and 1990 and 1992, respectively.

Setting

General community.

Participants

6180 mother-child pairs with measures of urinary iodine and creatinine concentrations in pregnancy and child IQ. Exclusion criteria were multiple pregnancies, fertility treatment, medication affecting the thyroid, and preexisting thyroid disease.

Main Outcome Measures

Child nonverbal and verbal IQ assessed at 1.5 to 8 years of age.

Results

There was a positive curvilinear association of urinary iodine/creatinine ratio (UI/Creat) with mean verbal IQ only. UI/Creat <150 µg/g was not associated with lower nonverbal IQ (-0.6 point; 95% CI: -1.7 to 0.4 points; P = 0.246) or lower verbal IQ (-0.6 point; 95% CI: -1.3 to 0.1 points; P = 0.082). Stratified analyses showed that the association of UI/Creat with verbal IQ was only present up to 14 weeks of gestation.

Conclusions

Fetal brain development is vulnerable to mild to moderate iodine deficiency, particularly in the first trimester. Our results show that potential randomized controlled trials investigating the effect of iodine supplementation in women with mild to moderate iodine deficiency on child neurodevelopment should begin supplementation not later than the first trimester.

Topics

By this author

Related research

Lifestyle and Environment › Nutrition and Metabolic Health › Dietary Patterns
Deborah Levie, Tim I M Korevaar, Sarah C Bath, Mario Murcia, Mariana Dineva, Sabrina Llop, Antonius E van Herwaarden, Yolanda B de Rijke, Jesús M Ibarluzea, Jordi Sunyer, Henning Tiemeier, Margaret P Rayman, Mònica Guxens, Robin P Peeters
Debbie Levie, Deb Levie, D Levie, Timothy Korevaar, T Korevaar, S Bath, M Murcia, M Dineva, S Llop, A Herwaarden, Y Rijke, J Ibarluzea, J Sunyer, H Tiemeier, Maggie Rayman, Peggy Rayman, M Rayman, M Guxens, R Peeters
PMID 30920622 30920622 DOI 10.1210/jc.2018-02559 10.1210/jc.2018-02559 Levie et al. 2019, Levie 2019

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