The physical and cognitive health of the developing infant depends on adequacy of this essential mineral
Iodine – you may know it as the topical preparation used before surgery for the purpose of disinfecting, or as just another element learned in chemistry courses of high school or college (which you have long forgotten). However, iodine is of great importance to your body daily, and is a crucial mineral for the function of the thyroid gland. Iodine often comes to our body from iodized salt – which actually was something implemented in many regions around the globe when historically it was realized that there were high levels of iodine deficiency. And now, as many of us turn to non-iodized sea salt or avoid salt (and the sodium it contains) altogether, iodine deficiency once again is becoming a common cause of hypothyroidism.
A 2018 survey of 273 pregnant women in Brazil, a country which implements salt-iodization programs, found that 52% of the women were iodine deficient and that salt iodization did not maintain iodine status within adequate and recommended ranges for pregnant women.
Population surveys have shown a high rate of iodine deficiency, defined as urinary iodine concentration (UIC) levels below 100 mcg/L. In 2003, 9.8% of adults, and 10.1% of school-aged children in the US had UIC levels below this threshold, while in Europe statistics were far worse with 56.9% and 59.9% of these populations, respectively, below the 100 mcg/L threshold. A 2018 survey of 273 pregnant women in Brazil, a country which implements salt-iodization programs, found that 52% of the women were iodine deficient and that salt iodization did not maintain iodine status within adequate and recommended ranges for pregnant women. So, despite being in a region considered “iodine adequate,” deficiency rates were alarmingly high in this population. Of these women, only 4.5% had a goiter – a physical sign considered indictive of iodine deficiency. Even in Japan, a region particularly known for their consumption of seaweed which contains very high levels of iodine, a 2012 survey of 934 pregnant women found that 16.1% had UIC levels showing deficiency.
Why does the developing infant need iodine?
Iodine deficiency is a common cause of fetal and neonatal hypothyroidism and may lead to preventable brain damage. Although severe iodine deficiency and related complications such as cretinism, a condition typified by stunted physical growth and mental development, have been nearly eliminated in developed countries due to newborn screening for iodine deficiency and hypothyroidism, there still can be impaired cognitive function during childhood or adolescence if iodine intake (of the gravid and nursing mother as well as the child) is not adequate.
2016 study of 89 children with attention-deficit hyperactivity disorder (ADHD) found that a shocking 71.9% were iodine deficient, calling into question if this mineral deficiency plays a significant role in the development (and maintenance) of this condition.
Experimental studies have helped further our understanding of the role thyroid hormone and iodine plays in cognitive development, showing that development of the cerebral cortex, a part of the brain that plays a key role in memory, attention, cognition, and language, can be irreversibly disturbed in the setting of iodine deficiency. A 2016 study of 89 children with attention-deficit hyperactivity disorder (ADHD) found that a shocking 71.9% were iodine deficient, calling into question if this mineral deficiency plays a significant role in the development (and maintenance) of this condition. Even the children of women, who when pregnant were shown to have UIC of 150 mcg/L or less (with only those lower than 100 mcg/L being considered deficient by current standards), were found to have lower educational performance in subjects of spelling, grammar, and English-literacy at nine years of age than their peers whose mothers had higher levels of iodine during pregnancy. Hearing impairment in children also may be associated with iodine deficiency.
Iodine in pregnancy and lactation
There is an increased need for iodine during pregnancy and lactation for multiple reasons. Maternal thyroid hormone production increases by approximately 50% in early pregnancy. The fetus begins to produce thyroid hormone during the second half of pregnancy, which further contributes to increased maternal iodine requirements. Iodine is readily transferred by the placenta to meet the needs of the fetus. Similarly, after delivery, the maternal body continues to work hard to ensure the needs of the fast-growing infant are met – which includes diverting essential vitamins and minerals such as iodine into the supply of breast milk which is feeding the newborn child. The concentration of iodine in the breast milk is 20 to 50 times that of the maternal blood, reflecting the high need for iodine transfer to the infant. However, this fast draws from the maternal reserves and intake – a time when a new mother never wants to be feeling depleted (although often is).
Fetal and neonatal iodine deficiency can be prevented with adequate iodine supplementation prior to conception and during pregnancy and lactation.
Fetal and neonatal iodine deficiency can be prevented with adequate iodine supplementation prior to conception and during pregnancy and lactation. Iodine requirements in pregnancy and lactation are 220 mcg/day and 290 mcg/day, respectively. Deficiency in these crucial times can in part be prevented by ensuring adequacy of this mineral prior to becoming pregnant. As rates of deficiency population-wide are high, consideration should be given for requesting this screening (best performed using a 24-hour UIC assessment) when thyroid hormones are assessed.
Most iodine that is taken in orally, whether in supplement or food form, is effectively absorbed in the gut. The bioavailability of iodine from potassium iodide is very high (96.4%) while the bioavailability of iodine from other sources vary. Further information about the how iodine is used by the thyroid gland, dietary sources, and recommended intake can be found in the discussion of iodine here.
Click here to see References
 de Benoist B, et al. Prevalence of iodine deficiency worldwide. The Lancet. 2003 Nov 29;362(9398):1859-60.
 Mioto VCB, et al. High prevalence of iodine deficiency in pregnant women living in adequate iodine area. Endocr Connect. 2018 May;7(5):762-767.
 Fuse Y, et al. Iodine status of pregnant and postpartum Japanese women: effect of iodine intake on maternal and neonatal thyroid function in an iodine-sufficient area. J Clin Endocrinol Metab. 2011 Dec;96(12):3846-54.
 Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408.
 Velasco I, et al. Iodine as Essential Nutrient during the First 1000 Days of Life. Nutrients. 2018 Mar 1;10(3). pii: E290.
 Kanık Yüksek S, et al. Evaluation of Iodine Deficiency in Children with Attention Deficit/Hyperactivity Disorder. J Clin Res Pediatr Endocrinol. 2016 Mar 5;8(1):61-6.
 Hynes KL, et al. Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort. J Clin Endocrinol Metab. 2013 May;98(5):1954-62.
 van den Briel T, et al. Mild iodine deficiency is associated with elevated hearing thresholds in children in Benin. Eur J Clin Nutr. 2001 Sep;55(9):763-8.
 Roti E, et al. Placental inner ring iodothyronine deiodination: a mechanism for decreased passage of T4 and T3 from mother to fetus. Trans Assoc Am Physicians. 1981;94:183-9.
 Glinoer D. Pregnancy and iodine. Thyroid. 2001 May;11(5):471-81.
 Tazebay UH, et al. The mammary gland iodide transporter is expressed during lactation and in breast cancer. Nat Med. 2000 Aug;6(8):871-8.
 Leung AM, et al. Iodine nutrition in pregnancy and lactation. Endocrinol Metab Clin North Am. 2011 Dec;40(4):765-77.
 Panel on Micronutrients; Subcommittees on Upper Reference Levels of Nutrients and of Interpretation and Use of Dietary Reference Intakes; Standing Committee on the Scientific Evaluation of Dietary Reference Intakes; Food and Nutrition Board; Institute of Medicine. Iodine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. The National Academies Press, 2001. 258-289.
 Aquaron R, et al. Bioavailability of seaweed iodine in human beings. Cell Mol Biol (Noisy-le-grand). 2002 Jul;48(5):563-9.