Consequences of iodine deficiency and excess in pregnant women: an overview of current knowns and unknowns,

Abstract

Severe iodine deficiency during development results in maternal and fetal hypothyroidism and associated serious adverse health effects, including cretinism and growth retardation. Universal salt iodization is the first-line strategy for the elimination of severe iodine deficiency. Iodine supplementation is recommended for vulnerable groups in severely iodine-deficient regions where salt iodization is infeasible or insufficient. A recent clinical trial has informed best practices for iodine supplementation of severely iodine-deficient lactating mothers. Because of successful programs of universal salt iodization in formerly severely iodine-deficient regions around the world, public health concern has shifted toward mild to moderate iodine deficiency, which remains prevalent in many regions, especially among pregnant women. Observational studies have shown associations between both mild maternal iodine deficiency and mild maternal thyroid hypofunction and decreased child cognition. Iodine supplementation has been shown to improve indexes of maternal thyroid function, even in marginally iodine-deficient areas. However, no data are yet available from randomized controlled trials in regions of mild to moderate iodine insufficiency on the relation between maternal iodine supplementation and neurobehavioral development in the offspring; thus, the long-term benefits and safety of such supplementation are uncertain. Although it is clear that excessive iodine intake can cause alterations in thyroid function in susceptible individuals, safe upper limits for iodine intake in pregnancy have not been well defined. Well-designed, prospective, randomized controlled trials that examine the effects of iodine supplementation on maternal thyroid function and infant neurobehavioral development in mildly to moderately iodine-deficient pregnant women are urgently needed. In addition, clinical data on the effects of iodine excess in pregnant and lactating women are needed to inform current recommendations for safe upper limits on chronic iodine ingestion in general and on iodine supplementation in particular.

Suboptimal Maternal Iodine Intake Is Associated with Impaired Child Neurodevelopment at 3 Years of Age in the Norwegian Mother and Child Cohort Study

“…2 Excludes iodine from supplements. 3 Mean 6 SD (all such values). 4 Any reported use of folic acid supplements from 4 wk before to 8 wk after conception reported in the general questionnaire (not in the FFQ).…”

“…Previous studies on iodine supplement use in pregnancy and child neurodevelopmental outcomes in areas with mild-to-moderate ID have shown inconsistent results (3,39,48), and to our knowledge there are no randomized controlled trials published to date. In this study we examined the associations in women with iodine intake from food below and above the EAR (160 mg/d) separately because the effect of supplemental iodine might depend on previous iodine status.…”

“…A recent systematic review estimated that introducing salt iodization in areas of chronic ID may increase mean intelligence quotients (IQs) by 8-10 points (2). Although the consequences of severe ID have been thoroughly investigated, less is known about the potential effects of mild-to-moderate ID during pregnancy (3). Results from 2 observational studies indicate that it might affect cognitive development negatively (4,5).…”

Iodine intake from supplements and diet during pregnancy and child cognitive and motor development: the INMA Mother and Child Cohort Study

“…Several studies have investigated the relationship between maternal thyroid function and child cognitive development,3 but this is not the same as studying the effect of iodine status, as maternal thyroid function may be affected by other factors apart from iodine intake, as it is the case for autoimmune disorders 4…”

Avaliação da suficiência de iodo e sua relação com a função tireoidiana materna em gestantes provenientes da cidade de São Paulo, SP

“…A deficiência grave de iodo durante a gestação pode resultar em hipotireoidismo materno e fetal com severas repercussões na prole, como cretinismo e retardo no desenvolvimento 82,83 . Mesmo deficiências leves de iodo podem cursar com disfunção tireoidiana materna e prejuízos no desenvolvimento neurológico das crianças 84 .…”