Jan 262017
Thyroxine T4 is made by the thyroid and uses Selenium, Zinc and Iodine. The Liver converts T4 to T3 triiodothyronine.
TSH causes the thyroid gland to make two hormones: triiodothyronine (T3) and thyroxine (T4).
A normal level of T4 on its own may not be an indicator of normal thyroid function, because if the thyroid can’t convert the T4 to T3, due to a mineral deficiency or problem thyroid, then the body is getting no benefit from the T4 in the blood stream.
Synthetic thyroxin such as Synthoid is T4, so if you are taking it, the T4 levels may show as correct even when the thyroid is not functioning properly.
Natural forms of desiccated thyroxin will normally contain a mix of both T4 and some T3.