When the body is deprived of iodine for a long period of time, thyroid hormone levels are reduced, which can cause an increase in the secretion of thyroid stimulating thyroid tissue cells to proliferate, increasing the size of the thyroid gland and resulting in an enlarged thyroid gland; the longer the iodine deficiency, the more pronounced the enlargement of the thyroid tissue. However, this enlarged thyroid gland can return to its normal size within a few months or years of iodine supplementation.