Which hormone imbalance can lead to an enlarged thyroid gland?

An enlarged thyroid gland, known as a goiter, is commonly associated with iodine deficiency. Iodine is essential for the synthesis of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). When the body lacks sufficient iodine, the thyroid cannot produce enough of these hormones. In an effort to compensate for the low hormone levels, the pituitary gland increases the secretion of thyroid-stimulating hormone (TSH). This overstimulation leads to the enlargement of the thyroid gland as it tries to produce more hormones, resulting in a goiter.

While high thyroxin levels can influence thyroid function, it typically does not lead to an enlargement; rather, it may result in atrophy or other dysregulatory symptoms. A T3 deficiency alone, while it can present its own set of issues, is less directly linked to physical enlargement of the gland compared to iodine deficiency. High estrogen levels may impact thyroid function in other ways but are not a primary cause of thyroid enlargement. Thus, iodine deficiency stands out as the most direct and well-understood cause of an enlarged thyroid gland due to its critical role in thyroid hormone production.