Iodine is an essential nutrient and an important component of thyroid hormones, which could not be formed without iodine. They are involved in the regulation of growth, bone formation, metabolism and brain development. Iodine is absorbed primarily via food and the iodine content of foodstuffs varies greatly depending on the region. Chronic iodine deficiency in older people may lead to the formation of nodules in the thyroid gland. Activating these with a sudden oversupply of iodine such as from seaweed products with extremely high iodine content can lead to hyperfunction of the thyroid gland (iodine-induced hyperthyroidism) which may have life threatening effects on the metabolism.
In a normally functioning thyroid, a sustained excess of iodine can inhibit the formation of thyroid hormones, a consequence of which can be an undersupply (iodine-induced hypothyroidism) and the formation of a goitre (Federal Institute for Risk Assessment (BfR), 2007).