Why are seaweeds important sources of iodine?

Seaweeds are important sources of iodine because they are capable of accumulating the element from their environment. While iodine is present in seawater only in sparse concentrations—approximately 50 mg per metric ton—seaweeds effectively concentrate this element within their tissues.1

Historically, this biological accumulation made seaweed a significant commercial source of iodine. The production process involved drying and burning the seaweed to create ash, which was then leached with water. Through a series of chemical treatments, including evaporation and the addition of manganese dioxide, the concentrated iodine could be released, vaporized, and purified via sublimation.2

Because the ocean is a primary reservoir for iodine, marine-based organisms like seaweed, as well as oysters and cod, serve as reliable dietary sources of this essential nutrient, which the human body requires for the production of thyroxine in the thyroid gland.123