Iodine is essential for the production of maternal and fetal thyroid hormones that regulate the development of the fetal brain and nervous system (1). A woman’s iodine requirements increase substantially during pregnancy to ensure adequate supply to the fetus (2). Globally, although nearly a third of school-age children (246 million) are estimated to have insufficient iodine intake (3), this commonly-used surrogate measure likely greatly underestimates the number of pregnant and lactating women with inadequate iodine nutrition status (4). Depending on the timing and severity, insufficient iodine intake increases the risk of negative reproductive outcomes, such as perinatal and infant mortality, and intellectual impairment, the most extreme form of which is cretinism (5).

Data indicates that while iodine status has improved among pregnant and lactating women in Europe, the eastern Mediterranean, Southeast Asia, and the Western Pacific regions, there has been little progress in the African region (3). Furthermore, mild gestational iodine deficiency can still be found in some European countries (6), and iodine intake may be low in pregnant women in the US based on median urinary iodine concentration readings just below the WHO cutoff of 150 μg/L (7). In nearly all regions affected by iodine deficiency, salt iodization is the most cost-effective way of delivering iodine (5, 8, 9). Global population coverage with iodized salt increased from 20% in 1990 to approximately 70% in 2013 (3). The annual costs of salt iodization are estimated to be US$0.02–0.05 per child covered, with the costs per child death averted at US$1,000 and US$34–36.6 per disability adjusted life year (DALY) gained (5). WHO and UNICEF recommend iodine supplementation for pregnant and lactating women in countries where less than 20% of households have access to iodized salt, until the salt iodization programme is scaled up. Countries with a household access to iodized salt between 20 and 90% should make efforts to accelerate salt iodization or assess the feasibility of increasing iodine intake in the form of a supplement or iodine fortified foods by the most susceptible groups (2).

There is some evidence that routine iodine supplementation in pregnancy may not be without risk (10). The safe upper limit in pregnancy is uncertain because the fetal thyroid is vulnerable to iodine excess. Congenital hypothyroidism in newborns has been reported in mothers who had an excessive dietary intake of iodine during pregnancy (11). Despite this, oral iodine supplementation is associated with infant survival (12) and reduced risk of cretinism (5). Results of randomized controlled trials currently under way in geographic areas of mild to moderate iodine deficiency should contribute to clarification of the issue (1, 2).

Salt iodization programmes are highly cost-effective when properly managed and compliant with legislation and/or regulations, although the quality and compliance vary by national programme and over time (5, 9). Where salt is not processed centrally in large factories, iodization is constrained by the use of relatively impure, locally sourced and prepared salt. Concerns have been raised, that salt iodization programmes may clash with efforts to reduce sodium intake for reducing the risk of elevated blood pressure and cardiovascular diseases. However, the public health goals of reducing sodium consumption and increasing iodine intake through salt iodization are compatible as the concentration of iodine in salt can be adjusted as needed.

Active monitoring is needed to ensure that the global public health gains made in improving iodine levels among pregnant and lactating women are maintained. Iodine supplementation is recommended as complementary to salt iodization programmes where indicated.

References

1. De-Regil LM, Harding KB, Peña-Rosas JP, Webster AC. Iodine supplementation for women during the preconception, pregnancy and postpartum period. Protocol. Cochrane Database of Systematic Reviews. 2015; Issue 6. Art. No.: CD011761.

2. WHO. Iodine supplementation in pregnant and lactating women. Geneva: World Health Organization; 2016. (http://www.who.int/elena/titles/iodine_pregnancy/en/)

3. Pearce EN, Andersson M, Zimmermann MB. Global Iodine Nutrition: Where Do We Stand in 2013? Thyroid. 2013; 23, Number 5, 1-6.

4. Wong EM, Sullivan KM, Perrine CG, Rogers LM, Peña-Rosas JP. Comparison of median urinary iodine concentration as an indicator of iodine status among pregnant women, school-age children, and nonpregnant women. Food and Nutrition Bulletin.2011; S32 (3): 206-212.

5. Zimmermann MB. The effects of iodine deficiency in pregnancy and infancy. Paediatric and Perinatal Epidemiology. 2012; 26(Suppl1): 108-117.

6. Trumpff C, De Schepper J, Tafforeau J, Van Oyen H, Vanderfaeillie J, Vandevijvere S. Mild iodine deficiency in pregnancy in Europe and its consequences for cognitive and psychomotor development of children: a review. J Trace Elem Med Biol. 2013; 27(3):174-83.

7. Gahche JJ, Bailey RL, Mirel LB, Dwyer JT. The prevalence of using iodine-containing supplements is low among reproductive-age women, NHANES 1999-2006. J Nutr. 2013; 143(6):872-7.

8. WHO and UNICEF. Reaching optimal iodine nutrition in pregnant and lactating women and young children. Joint statement by WHO and UNICEF. Geneva: World Health Organization; 2007. (www.who.int/nutrition/publications/micronutrients/WHOstatement_IDD_pregnancy.pdf)

9. Guideline: fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders. Geneva: World Health Organization; 2014. (http://www.who.int.elena/en/)

10. Zhou SJ, Anderson AJ, Gibson RA, Makrides M. Effect of iodine supplementation in pregnancy on child development and other clinical outcomes: a systematic review of randomized controlled trials. American Journal of Clinical Nutrition. 2013; 98:1241-1254.

11. Connelly KJ, Boston BA, Pearce EN, Sesser D, Snyder D, Braverman LE, Pino S, LaFranchi SH. Congenital hypothyroidism caused by excess prenatal maternal iodine ingestion. Journal of Pediatrics. 2012; 161:760–2.

12. Cobra C, Muhilal, Rusmil, K, et al. Infant survival is improved by oral iodine supplementation. Journal of Nutrition. 1997; 127: 574–578.

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Conflict of interest statements were collected from all named authors and no conflicts were identified.