150 µg/day (adults); 220–290 µg/day in pregnancy and breastfeeding. Iodized salt covers most people.
Corrects the deficiency and prevents goiter and developmental damage (cretinism).
View the study (review) →Deficiency during pregnancy harms the baby's brain development.
View the study (systematic review) →⏱ 3 min read
Iodine is a trace mineral whose only known biological function is to serve as a structural component of the thyroid hormones (thyroxine T4 and triiodothyronine T3), which are responsible for regulating basal metabolism, thermogenesis, bone growth, fetal brain development, and the maturation of the nervous system in the first years of life; this unique but critical function explains why iodine deficiency is one of the most important preventable causes of cognitive delay and brain damage worldwide, a 20th-century public health emergency that universal iodization of table salt reduced drastically without eliminating entirely.
Spain is a country with traditionally insufficient iodization: although iodized salt has been available since the 1980s, its penetration in the population is suboptimal and consumption of oily fish (another important source) has declined in recent decades; population urinary iodine studies show average figures at the lower limit of the optimal range and, in certain groups (pregnant women, young children, women of childbearing age), a prevalence of mild to moderate iodine deficiency that justifies specific public health interventions.
The indication with the greatest clinical relevance is supplementation during pregnancy and breastfeeding: iodine needs increase by 50 percent during gestation because the mother must provide the iodine needed for hormone synthesis by her own hyperactivated thyroid and for fetal brain development; moderate to severe deficiency during the first trimester is associated with reductions in intelligence quotient in the offspring, a robust association documented in large cohorts.
International guidelines (WHO, the Spanish Society of Endocrinology and Nutrition) recommend supplementation with 150-200 micrograms per day of potassium iodide throughout gestation and breastfeeding, ideally starting before conception; this recommendation applies universally except in people with active autoimmune thyroiditis, in whom supplementation must be individualized because of the risk of exacerbation.
In non-pregnant adults with adequate iodine, supplementation provides no clinical benefit and, in people with autoimmune thyroiditis or autonomous thyroid nodules, may precipitate thyroid dysfunction (hypothyroidism or hyperthyroidism); iodine supplementation in adults is indicated only if there is a deficiency documented by urinary iodine or by a specific clinical situation.
There are preliminary data that supplementation with molecular iodine (not iodide) at doses of 3-6 milligrams per day could improve symptoms of fibrocystic breast disease in premenopausal women, a traditional indication supported by a small clinical trial but which has not entered conventional clinical guidelines because of the heterogeneity of the data and concerns about thyroid function with sustained high doses.
The nutritional doses are 150 micrograms per day in non-pregnant adults and 200 micrograms in pregnancy and breastfeeding (preferably as potassium iodide, the most studied and best-tolerated form); the established safe upper limit is 1,100 micrograms per day in adults, a figure that is very easy to exceed with non-standardized seaweed supplements (kelp, dulse), which can contain enormous and variable amounts of iodine.
The most important precaution is not to exceed high doses chronically: both deficiency and excess can precipitate thyroid dysfunction (the Wolff-Chaikoff or Jod-Basedow effect), especially in people with autoimmune thyroiditis, thyroid nodules, or a predisposition to thyroid disease; seaweed supplements are problematic because of their unpredictable content and should be avoided in favor of standardized potassium iodide; people with known thyroid disease should individualize supplementation with their endocrinologist; pregnancy is where it matters most to ensure adequate supplementation, ideally started before conception.
Information, not medical advice. Scientific evidence reflects the quality of the studies.