What is critical to the synthesis of thyroxin, the hormone that controls the rate of oxygen use by cells, and whose deficiency causes the condition known as goiter?

I believe that the mineral iodine is critical to the synthesis of thyroxine.  The hormone thyroxine is secreted in to the blood stream by thryroid hormone. It plays an important role in heart and digestive function, metabolism, brain development, bone health, and muscle control. This means it affects almost all of the body's systems and thus proper levels are vital for health.

Cbecause it is the only one describing a habitat