Which of the following summarizes iodine's role and dietary sources?

• A. Iodine is not essential for thyroid function.
• B. Excess iodine intake is always harmless.
• C. Iodine is primarily stored in bones.
• D. Iodine is essential for thyroid function; common dietary sources include iodized salt, seafood, and dairy.

Answer: (D)

Iodine is essential for thyroid hormone production, which governs metabolism and supports growth and brain development. The thyroid concentrates iodine from the bloodstream to make thyroid hormones, mainly T4 and T3, that circulate to regulate energy use, temperature, and development. Iodine isn’t stored in bones; it’s taken up by the thyroid and used to build hormones. Common dietary sources include iodized salt, seafood, and dairy products, which help most people meet their daily needs. When iodine intake is inadequate, thyroid hormone production falls, leading to goiter and potential developmental issues if deficiency occurs during pregnancy. Although iodine is needed in proper amounts, excessive intake can also disrupt thyroid function in some individuals. This makes the statement describing iodine’s essential role and typical dietary sources the accurate summary.