Why is the element iodine necessary for vertebrates?

Iodine is necessary for vertebrates primarily because it is an essential element of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a critical role in regulating metabolism, growth, and development in the body. Without sufficient iodine, the thyroid cannot produce these hormones effectively, which can lead to conditions such as goiter (enlargement of the thyroid gland) and various metabolic disorders.

The importance of iodine in hormone production underscores its role in maintaining overall health and metabolic function, making it a vital nutrient for vertebrates.