Goiter, or enlargement of the thyroid gland, is usually the earliest visible symptom of iodine deficiency. (Goiter can occur for many other reasons as well, but iodine deficiency is among the most common causes worldwide.) The enlargement of the thyroid results from overstimulation of the thyroid gland by thyroid stimulating hormone (TSH), as the body attempts to produce increased amounts of thyroid hormone.Goiter is more common in certain geographical areas of the world where iodine is lacking in the diet and where selenium is lacking in the soil. (Selenium is directly involved with certain activities of the thyroid gland.)