Iodine plays a major role in which bodily process?

Iodine is crucial for thyroid function because it is a key component in the synthesis of thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3). These hormones are essential for regulating various metabolic processes in the body, including growth, development, and energy metabolism. Without adequate iodine intake, the thyroid cannot produce enough hormones, which can lead to conditions such as hypothyroidism or goiter.

While the other options pertain to bodily processes that are important in their own right, they do not directly involve iodine. For example, vitamin absorption primarily involves the small intestine and various vitamins, while muscle recovery is influenced by protein, hydration, and rest. Calcium metabolism is mainly regulated by vitamin D and parathyroid hormone. Thus, iodine's specific and vital role in thyroid function makes it the correct answer for this question.