Like all of our glands, the thyroid requires specific nutrients, either from food or supplements, for optimal functioning. These nutrients act as precursors to thyroid function. Thyroid-stimulating hormone must signal cells to synthesize thyroxine. Thyroxine, also known as T4, must be converted into active T3. For this cascade to occur properly, cortisol and insulin levels must be well controlled, and the necessary precursors and coenzymes must be available.