Iodine (Elemental I)

Direct Answer

Iodine is an essential halogen trace element required exclusively as an essential structural component of thyroid hormones thyroxine (T4) and triiodothyronine (T3), regulating metabolic rate, cellular respiration, and fetal neurodevelopment. Adult RDA is 150 µg, with an Upper Limit of 1,100 µg/day.

Source: NIH ODS / WHO / EFSA · Last reviewed Aug 28, 2026

Specs

Nutrient Type	Essential Trace Halogen Element
Adult RDA / RDI	150 µg / day (220 µg pregnancy / 290 µg lactation)
Tolerable Upper Limit (UL)	1,100 µg / day (Avoid Wolff-Chaikoff thyroid autoregulatory shutdown)
Chemical Forms	Iodide (I- / Potassium Iodide KI, Potassium Iodate KIO3 in iodized salt), Molecular Iodine
Primary Biological Function	Constituent of Thyroxine (T4, 4 iodine atoms / 65% by weight) and Triiodothyronine (T3, 3 iodine atoms / 59% by weight)
Deficiency Condition	Endemic Goiter (Compensatory thyroid enlargement), Congenital Hypothyroidism / Cretinism (Permanent neurodevelopmental impairment), Maternal miscarriages
Top Whole Food Sources	Kombu Kelp, Nori Seaweed, Atlantic Cod, Eastern Oysters, Iodized Table Salt, Greek Yogurt, Dairy Milk, Eggs
Iodized Salt Public Health Impact	Universal salt iodization (45–75 mg KI / kg salt) is hailed as one of the greatest global public health achievements, eradicating cretinism worldwide

Thyroid Sodium-Iodide Symporter (NIS)

Thyroid follicular cells actively concentrate iodide from blood plasma at a 20:1 to 40:1 ratio against electrochemical gradients via the basolateral Sodium-Iodide Symporter (NIS), coupling 2 Na+ ions per 1 I- ion.