Associations between maternal urinary iodine assessment, dietary iodine intakes and neurodevelopmental outcomes in the child: a systematic review

Abstract

Objective Mild to moderate iodine deficiency during pregnancy has been associated with adverse neurodevelopmental outcomes in offspring. Few research studies to date combine assessment of urinary iodine (UIC and/or ICr), biomarkers that best reflect dietary intake, with reported dietary intake of iodine rich foods in their assessment of iodine deficiency. Thus, a systematic review was conducted to incorporate both these important measures. Design Using PRISMA guidelines, a comprehensive search was conducted in three electronic databases (EMBASE®, MedLine® and Web of Science®) from January 1970–March 2021. Quality assessment was undertaken using the Newcastle Ottawa Scale. Eligible studies included reported assessment of iodine status through urinary iodine (UIC and/or ICr) and/or dietary intake measures in pregnancy alongside neurodevelopmental outcomes measured in the children. Data extracted included study author, design, sample size, country, gestational age, child age at testing, cognitive tests, urinary iodine assessment (UIC in μg/L and/or ICr in μg/g), dietary iodine intake assessment and results of associations for the assessed cognitive outcomes. Results Twelve studies were included with nine reporting women as mild-moderately iodine deficient based on World Health Organization (WHO) cut-offs for urinary iodine measurements < 150 μg/l, as the median UIC value in pregnant women. Only four of the nine studies reported a negative association with child cognitive outcomes based on deficient urinary iodine measurements. Five studies reported urinary iodine measurements and dietary intakes with four of these studies reporting a negative association of lower urinary iodine measurements and dietary iodine intakes with adverse offspring neurodevelopment. Milk was identified as the main dietary source of iodine in these studies. Conclusion The majority of studies classified pregnant women to be mild-moderately iodine deficient based on urinary iodine assessment (UIC and/or ICr) and/or dietary intakes, with subsequent offspring neurodevelopment implications identified. Although a considerable number of studies did not report an adverse association with neurodevelopmental outcomes, these findings are still supportive of ensuring adequate dietary iodine intakes and urinary iodine monitoring throughout pregnancy due to the important role iodine plays within foetal neurodevelopment. This review suggests that dietary intake data may indicate a stronger association with cognitive outcomes than urinary iodine measurements alone. The strength of this review distinguishes results based on cognitive outcome per urinary iodine assessment strategy (UIC and/or ICr) with dietary data. Future work is needed respecting the usefulness of urinary iodine assessment (UIC and/or ICr) as an indicator of deficiency whilst also taking account of dietary intakes.

Iodine: Physiological importance and food sources

“…Studies on the association between maternal iodine in urine, dietary intake, and neurodevelopmental consequences on the offspring show no uniform approach in the investigation, as was reviewed by Monaghan et al (2021). Urin is sampled at different gestational ages (13th-28th week), children are also examined at different ages (4-14 years) and different methodologies are applied to assess their development, behavior, and skills.…”

The Impact of Iodine Concentration Disorders on Health and Cancer

“…In pregnant women, iodine deficiency may result in severe neurological deficits and the formation of goiter in their offspring. Lower degrees of iodine deficiency may also cause significant neurodevelopmental deficits in infants and children [ 44 , 46 ]. The most serious consequence of iodine deficiency is damage to the fetus.…”

Results of the national biomonitoring program show persistent iodine deficiency in Israel

“…Iodine deficiency (ID), particularly during early childhood, may result in the development of one or multiple iodine deficiency disorders (IDD). These range from impaired thyroid function and lost intellectual potential (in mild to moderate cases), to goiter, hypothyroidism, and cretinism (in more severe cases) [ 2 – 4 ]. Iodine intake is especially critical for pregnant women, as fetal brain development is vulnerable to even mild iodine deficiency.…”