Which statement about iodine and thyroid hormones is true?

Which statement about iodine and thyroid hormones is true?

• A. Iodine deficiency has no effect on thyroid function
• B. Iodine is used only in parathyroid function
• C. Iodine reduces TSH production
• D. Iodine is essential for the synthesis of thyroid hormones

Answer: (D)

Iodine is essential for the synthesis of thyroid hormones. The thyroid traps iodide, oxidizes it, and incorporates it into thyroglobulin to form MIT and DIT, which then couple to make T3 and T4. Without iodine, these steps cannot proceed, so thyroid hormone production drops and the pituitary responds by increasing TSH to stimulate the gland. This direct link means iodine deficiency clearly impairs thyroid hormone production. The other statements aren’t correct: iodine isn’t used in parathyroid function, and iodine doesn’t directly reduce TSH; thyroid hormone levels themselves regulate TSH through negative feedback.

Iodine is essential for the synthesis of thyroid hormones. The thyroid traps iodide, oxidizes it, and incorporates it into thyroglobulin to form MIT and DIT, which then couple to make T3 and T4. Without iodine, these steps cannot proceed, so thyroid hormone production drops and the pituitary responds by increasing TSH to stimulate the gland. This direct link means iodine deficiency clearly impairs thyroid hormone production. The other statements aren’t correct: iodine isn’t used in parathyroid function, and iodine doesn’t directly reduce TSH; thyroid hormone levels themselves regulate TSH through negative feedback.