Thyroid Hormone

The thyroid gland is one of the largest endocrine glands in the body located in the lower part of the neck. It produces thyroid hormones which play a major role in energy and metabolism. The thyroid does this by controlling the speed of energy usage, protein production, and sensitivity of all hormones in the body.
A healthy thyroid produces several hormones such as T1, T2, T3 (triiodothyronine), T4 (thyroxine) and calcitonin. In humans, the ratio of T4 to T3 is roughly 20 to 1. T4 is converted to the active hormone T3 which stimulates metabolism. The body, especially the liver, constantly converts T4 to Reverse T3 (RT3) to eliminate excess T4 in the body. In any given day, 40% of T4 is converted into T3 and 20% is converted to Reverse T3. But in any situation where the body needs to store energy and use it on something else such as in a stressful situation, these conversions can change – RT3 conversion can go as high as 50% or more and the T3 level goes down. When biological stress is excessive, the adrenal glands produce high amounts of the stress hormone called cortisol to help cope up with the situation and achieve balance or stability (homeostasis). The excess cortisol inhibits the conversion of T4 to T3 by affecting the ability of the pituitary gland to produce thyroid-stimulating hormone.