Iodine: Beyond the Thyroid — Breast Tissue, Goitrogens & More

Iodine is best known as the mineral the thyroid needs to produce thyroid hormones (T3 and T4). But iodine receptors exist in other tissues too — including breast tissue, salivary glands, the gastric mucosa, and the choroid plexus — suggesting broader biological roles that are still being explored.

Thyroid Hormone Production

The thyroid gland concentrates iodine to about 30 times blood levels, using it to synthesize thyroxine (T4, with four iodine atoms) and triiodothyronine (T3, with three). Selenium-dependent deiodinase enzymes then convert T4 to the active T3 in peripheral tissues. Both iodine and selenium must be adequate for proper thyroid function.

Goitrogens

Goitrogens are compounds that interfere with iodine uptake or thyroid hormone production. They're found in cruciferous vegetables (broccoli, cabbage, kale), soy products, and some root vegetables. Cooking reduces goitrogenic activity significantly. In people with adequate iodine intake, normal consumption of these foods is not a clinical concern.

Food Sources

Seaweed (especially kelp, but beware of excess), iodized salt, cod, dairy products, shrimp, and eggs provide dietary iodine. Iodine content in plant foods depends entirely on soil iodine levels, which vary geographically.

External resources: NIH — Iodine Fact Sheet