Iodine, found in seafood and iodized salt, is essential for healthy thyroid function. The thyroid uses iodine to produce thyroxine (T4) and triiodothyronine (T3), hormones that help regulate metabolism, growth, and development.
Iodine occurs naturally in foods including seaweed, fish, shellfish, dairy products, and eggs. Iodized salt was introduced as a public-health measure because soil iodine levels vary widely, and low-iodine diets can cause deficiency. Adding a small, standardized amount to table salt dramatically reduced deficiency-related thyroid disease in many countries.
A common mix-up is confusing iodine with iodide. Iodide is the chemically reduced form commonly present in foods and supplements, while “iodine” is the familiar nutritional name. Another misconception is that all sea salt supplies iodine; most specialty and sea salts are not iodized unless the label says so.
Too little iodine can reduce thyroid-hormone production and enlarge the thyroid, causing a goiter. The recommended intake for most adults is 150 micrograms per day, rising to 220 micrograms during pregnancy.