enlargement of the thyroid gland Goiter is one of the earliest and most visible signs of iodine deficiency The thyroid enlarges in response to persistent stimulation by TSH (see Function) In mild iodine deficiency, this adaptation response may be enough to provide the body with sufficient thyroid hormone However, more severe cases of iodine deficiency result in hypothyroidism Thyroid enlargement may also be caused by factors other than iodine deficiency, especially in iodine sufficient countries, such as the U S