How does the thyroid gland respond when iodine intake is too low?

When iodine intake is insufficient, the thyroid gland cannot produce adequate amounts of thyroid hormones, as iodine is a critical component of their synthesis.123

In response to this decrease in circulating thyroid hormones, the pituitary gland increases its secretion of thyrotropin, also known as thyroid-stimulating hormone (TSH). This hormonal feedback mechanism triggers two primary responses:13

• Increased Iodine Uptake: The elevated thyrotropin levels stimulate the thyroid to capture available iodine more aggressively to facilitate hormone production.14
• Glandular Growth: Thyrotropin also stimulates the growth of thyroid cells. While this compensatory mechanism aims to restore normal hormone output, the persistent stimulation leads to the enlargement of the thyroid gland, a condition known as goitre.143

In children and adolescents, this goitre may regress if iodine intake is increased; however, in adults, the gland often becomes nodular and may not return to its normal size.13