What Iodine Actually Does in Your Body

Thyroid function

The thyroid concentrates iodine 20–40 times higher than blood using the sodium-iodide symporter (NIS). Inside the gland, thyroid peroxidase (TPO) oxidizes iodide, attaches it to tyrosine, and couples those pieces into T3 and T4 — the hormones that set your metabolic rate, support brain development, drive heart output, and influence cholesterol, mood, and cognition.

Why selenium matters here: making thyroid hormone generates hydrogen peroxide, which can damage the gland. Selenium-dependent enzymes neutralize that peroxide and also convert T4 into active T3. Taking iodine without adequate selenium invites oxidative stress on the thyroid — which is why selenium comes first.

Beyond the thyroid

  • Breast: concentrates iodine via NIS; elemental iodine has antiproliferative effects, and deficiency is linked to fibrocystic breast disease.
  • Ovaries: hold the second-highest iodine concentration after the thyroid; cysts are associated with deficiency.
  • Prostate: concentrates iodine and may share the breast’s antiproliferative benefit.
  • Stomach & salivary glands: use iodine for antimicrobial defense.
  • Brain, eyes, thymus, placenta: all rely on iodine for development, immunity, and fetal supply.

This is the core insight: iodine isn’t only a “thyroid nutrient.” Many tissues want it, and that’s why whole-body sufficiency takes more than the goiter-preventing minimum.

Sources

Compiled by Dr. Jason Dean from open scientific literature and the reference above. Educational only — not medical advice, and not evaluated by the FDA. Consult a qualified healthcare provider before changing your supplement, diet, or health routine.