Insufficient iodine intake can lead to intellectual developmental delays, goitre, hypothyroidism and other conditions collectively known as iodine deficiency disorders (IDD). Mild iodine deficiency can result in chronic thyroid hyperfunction. Correcting mild iodine deficiency can reduce the prevalence of hyperthyroidism, a condition that can be life-threatening. Chronic iodine deficiency may lead to compensatory hyperplasia of the thyroid gland accompanied by goitre, caused by elevated TSH concentrations. Goitre is initially diffuse but may progress to a nodular form in later stages, with the development of autonomous nodules. Goitre increases the risk of thyroid cancer. Iodine is essential for the biosynthesis of thyroid hormones, which influence all metabolic processes in the body from the foetal stage through to old age. Iodine deficiency is the most significant risk factor for thyroid disease and is the leading cause of preventable brain damage worldwide.