title: 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.
authors.affiliation: Section of Endocrinology, Diabetes, and Nutrition, Boston University School of Medicine, Boston, MA; elizabeth.pearce@bmc.org.
authors.forename: Elizabeth N
authors.identifier: 0000-0003-3799-0354
authors.initials: EN
authors.lastname: Pearce
authors.affiliation: Thyroid Research Group, Institute of Molecular and Experimental Medicine, Cardiff University, University Hospital of Wales, Cardiff, United Kingdom;
authors.forename: John H
authors.initials: JH
authors.lastname: Lazarus
authors.affiliation: Department of Nuclear Medicine, Hôpital Erasme, Université Libre de Bruxelles, Brussels, Belgium; and.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Moreno-Reyes
authors.affiliation: Human Nutrition Laboratory, Institute of Food, Nutrition, and Health, ETH Zurich, Zurich, Switzerland.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Zimmermann
mesh_terms: D002657:Child Development / Q000187:drug effects*; D003677:Deficiency Diseases / Q000150:complications / Q000517:prevention & control; D019587:Dietary Supplements / Q000009:adverse effects; D005260:Female; D006801:Humans; D007223:Infant; D007455:Iodine / Q000008:administration & dosage* / Q000009:adverse effects / Q000172:deficiency / Q000627:therapeutic use; D044343:Overnutrition / Q000150:complications; D011247:Pregnancy; D011248:Pregnancy Complications; D013961:Thyroid Gland / Q000187:drug effects*
chemical_list: D007455:Iodine
keywords: clinical trials; intervention outcomes; iodine supplementation; prenatal nutrition; public health