# item.guide
Side-by-Side Comparison Essential Vitamins & Minerals

Iodine (Elemental I) vs. Selenium (Elemental Se)

Comparing 2 standards across 9 specifications. 9 key differences identified.

Comparing:
Iodine (Elemental I)
Selenium (Elemental Se)

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.

View full Iodine (Elemental I) spec sheet →

Selenium is an essential trace element incorporated as Selenocysteine (the 21st amino acid) into 25 human selenoproteins including Glutathione Peroxidases (GPx) and Iodothyronine Deiodinases (T4->T3 conversion). Adult RDA is 55 µg, with a Tolerable Upper Limit of 400 µg/day.

View full Selenium (Elemental Se) spec sheet →

Specification Comparison Table

9 Parameters
Parameter / Spec
Nutrient Type
Essential Trace Halogen Element Essential Trace Element
Adult RDA / RDI
150 µg / day (220 µg pregnancy / 290 µg lactation) 55 µg / day (60 µg pregnancy, 70 µg lactation)
Tolerable Upper Limit (UL)
1,100 µg / day (Avoid Wolff-Chaikoff thyroid autoregulatory shutdown) 400 µg / day (Avoid selenosis / garlic breath, hair/nail brittleness)
Chemical Forms
Iodide (I- / Potassium Iodide KI, Potassium Iodate KIO3 in iodized salt), Molecular Iodine Selenomethionine (Plant organic), Selenocysteine (Animal selenoprotein), Sodium Selenite / Selenate (Inorganic)
Primary Biological Function
Constituent of Thyroxine (T4, 4 iodine atoms / 65% by weight) and Triiodothyronine (T3, 3 iodine atoms / 59% by weight) Glutathione Peroxidase (GPx1-4) lipid hydroperoxide neutralization, Iodothyronine Deiodinases (Converts thyroid T4 into active T3), Thioredoxin Reductase (TXNRD)
Deficiency Condition
Endemic Goiter (Compensatory thyroid enlargement), Congenital Hypothyroidism / Cretinism (Permanent neurodevelopmental impairment), Maternal miscarriages Keshan Disease (Endemic juvenile cardiomyopathy), Kashin-Beck Disease (Deforming osteoarthropathy), Impaired thyroid metabolism
Top Whole Food Sources
Kombu Kelp, Nori Seaweed, Atlantic Cod, Eastern Oysters, Iodized Table Salt, Greek Yogurt, Dairy Milk, Eggs Brazil Nuts (1 single nut provides ~70–90µg / 130–160% RDA), Eastern Oysters, Yellowfin Tuna, Halibut, Sardines, Beef Liver, 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
Soil Selenium Geographical Variability
Plant selenium reflects regional soil content; volcanic soils (South America, Great Plains) are rich, while parts of China, Scandinavia, and New Zealand are depleted