TL;DR

  • Iodine is essential not only for thyroid hormone production but also for brain development and cognitive function.

  • As of 2024, ~30% of the world’s population remains iodine-deficient (WHO).

  • Deficiency in children is linked to lower IQ, slower learning, and impaired motor and memory skills.

  • Newer studies show both too little and too much iodine can harm cognition — balance matters, especially in pregnancy and childhood.

Why Iodine Matters Beyond the Thyroid

We often think of iodine only in terms of thyroid health, but its role extends much further. A review in The Lancet (1998) estimated that 1.5 billion people were at risk of brain damage due to iodine deficiency.

One trial in the American Journal of Clinical Nutrition (2009) studied 184 children aged 10–13 with mild iodine deficiency. Those given 150 mcg of iodine daily for 28 weeks showed improved iodine status and better performance on two of four cognitive tests. This research highlighted that even mild deficiency can slow learning.

Newer Research on Iodine and Cognition

  • Iodine supplementation improves cognition in children
    A recent randomized controlled trial showed that iodine supplementation improved working memory, fine motor skills, and visual problem-solving in schoolchildren who were mildly deficient.(Biology (Basel). 2022 Oct 14;11(10):1507).

  • Too much is also a problem
    The study Association between Elevated Iodine Intake and IQ among School-Age Children found that children with very high iodine levels had lower IQs compared to those with moderate intake, suggesting a U-shaped curve of risk. (Nutrients. 2022 Oct 26;14(21):4493.)

  • Children under 5 years old
    A review confirmed that infants and young children in iodine-deficient areas show deficits in mental development, and that correcting deficiency is associated with gains in IQ and cognitive outcomes. (Nutrients. 2013 Apr 22;5(4):1384–1416).

Problems Can Start in the Womb

Iodine is particularly crucial during pregnancy. Both low and high maternal iodine levels can negatively impact child development.

  • Maternal iodine status & child cognition
    A recent Journal of Nutrition study found that children of mothers in the lowest or highest quartiles of iodine intake performed worse on language and cognitive tests than those of mothers in the mid-range. (Journal of Nutrition)

  • Public health impact
    UNICEF reports that even mild iodine deficiency during pregnancy can lead to measurable IQ losses in children (on the order of 8–10 points). (UNICEF)

Practical Takeaways

  • Adequate iodine is critical during pregnancy and early childhood.

  • Both deficiency and excess can impair brain function — balance is key.

  • Iodized salt, seafood, and dairy are common dietary sources; supplements may be appropriate under professional guidance.

FAQ

Q: How much iodine do adults need daily?
About 150 mcg/day for adults, 220 mcg/day in pregnancy, and 290 mcg/day while breastfeeding (NIH).

Q: Can too much iodine harm the brain?
Yes. Excessive iodine may cause thyroid dysfunction and is associated with lower IQ in children when intake is too high.

Q: Should all pregnant women take iodine supplements?
Many prenatal vitamins include iodine, but adequacy depends on diet and region. Best to confirm with a doctor trained in natural healthcare.