Glucose is required to convert thyroxin (T4) to its active form, triiodothyronine or liothyronine (T3). This occurs mainly in the liver, if glucose is adequate. Why? Glucose activates sulfhydryl enzymes that convert T4 to T3. What happens when T3 is not produced, whatever the cause — stress, radiation, environmental toxins, excess dietary estrogen or liver problems? When T3 decreases, the respiratory or mitochondrial enzymes do not work. T3 is essential for activating the electron transport chain down to the production of oxygen. When T3 is inadequate, sugar (glucose) is burned inefficiently to lactic acid instead of all the way to carbon dioxide. So, the body gets less energy from the same amount of glucose. When the liver runs out of stored sugar (glycogen), it stops converting T4 to T3.
The overall effect of this is low blood sugar, leading to increased adrenalin to compensate for the deficiency of energy, glucose and oxygen. Low thyroid patients excrete 10-40 times the normal amounts of adrenalin metabolites. At first, adrenalin attempts to mobilize glycogen and stored fat. Then progesterone is converted to cortisol in the adrenal cortex by a complex pathway involving a pituitary hormone (ACTH), which is released in response to adrenalin. Cortisol increases blood sugar via the catabolism of protein. Increased cortisol can decrease adrenalin and lead to a low pulse, common in hypothyroid people. But, if the adrenal cortex becomes exhausted and cannot produce enough cortisol, adrenalin will rise. Adrenalin-dominant people may have a high pulse around 120-150 but are still hypothyroid. In either case, proper thyroid therapy will normalize the resting pulse to the optimum, 85 beats per minute. The production of cortisol is a life-saving response to stress, but in the hypothyroid person, it occurs abnormally in an attempt to keep the blood sugar up. Cortisol, like estrogen, inhibits the thyroid, creating a vicious cycle that can only be broken by proper hormone balancing, such as thyroid therapy, and by opposing cortisone and/or estrogen with pregnenolone and progesterone, respectively. In addition, excess cortisol can lead to hot flushes or night sweats, diabetes, bone loss and glaucoma.