TL;DR

• Iodine is required to produce thyroid hormones.
• Deficiency can lead to goiter, hypothyroidism, and impaired brain development.
• Even mild iodine deficiency may affect learning and cognitive performance in children.
• Both deficiency and excess iodine can disrupt thyroid function.
• Adequate iodine intake is especially important during pregnancy.

Iodine: Updated Context

Iodine is an essential nutrient required for the production of thyroid hormones, which are critical for growth, metabolism, and neurodevelopment. Severe iodine deficiency remains a global public health concern, particularly in regions without iodized salt programs.

Earlier reviews, including those published in The Lancet and the Journal of Clinical Endocrinology & Metabolism, documented the well-established consequences of iodine deficiency, such as goiter, hypothyroidism, impaired fetal and childhood brain development, and increased risks during pregnancy. These effects are most pronounced with moderate to severe deficiency. Read about how hypothyroidism is often missed.

More recent research has focused on mild iodine deficiency, which can still be relevant in certain populations. A randomized, placebo-controlled trial published in the American Journal of Clinical Nutrition (2009; 90(5):1264–1271) found that iodine supplementation in mildly iodine-deficient school-aged children improved iodine status and led to improvements on some cognitive performance measures. Other observational studies have linked low iodine status with slower learning in children.

Iodine status is particularly important during pregnancy and early childhood, when thyroid hormone is critical for brain development. At the same time, excess iodine intake can disrupt thyroid function in susceptible individuals, sometimes triggering hyperthyroidism or hypothyroidism. Read more about thyroid function during pregnancy.

Current recommended iodine intakes are approximately 150 mcg per day for non-pregnant adults and 220–290 mcg per day during pregnancy and lactation, depending on the guideline source. These values are designed to prevent deficiency at a population level, though individual needs may vary.

Selenium is also important for thyroid function, click to read more.