Final answer:
Hypothyroidism occurs when the thyroid gland produces insufficient amounts of thyroid hormones. Iodine deficiency is the most common cause of hypothyroidism worldwide and can result in the development of goiter. The enlarged thyroid gland cannot increase hormone output due to the lack of iodine in the diet.
Step-by-step explanation:
Hypothyroidism occurs when the thyroid gland produces insufficient amounts of thyroid hormones. It can result from surgical removal of the thyroid. However, worldwide, the most common cause of hypothyroidism is dietary iodine deficiency. In cases of iodine deficiency, the negative feedback loop controlling the release of thyroid hormone causes repeated stimulation of the thyroid. This results in the thyroid gland growing in size and producing a goiter. Although the gland gets larger, it cannot increase hormone output because of the lack of iodine in the diet.