Originally Posted by moon8466
Every time I research this issue, it comes back to a probable thyroid problem. Can anyone provide any information or where else to look for the cause?
It's a little bit like the chicken and the egg, Moon, when it comes to where do you look.
Low thyroid function causes a lowered metabolic rate, which means that everything slow down, including body temperature. And then a low body temperature makes everything stay down.
T3 is the hormone that drives metabolism at a celluar level. The body makes a little T3 via the thyroid, however, most of the body's T3 production occurs in the peripheral tissues of the body through conversion of T4 to T3 by a deiodinating enzyme called 5-prime-deiodinase. The body also has the option to turn T4 peripherally into Reverse-T3 which is completely inactive. Metabolic rate is therefore determined by how much T4 gets converted to T3 and how much gets converted to Reverse-T3. And the metabolic rate determines how much heat the cells of the body produce, which in turn determines body temperature.
In times of stress conversion of T4 into T3 lowers and conversion into Reverse T3 increases - causing metabolims to slow and body temperature to lower. Conversely, in patients who are hyperthyroid the body produces too much T3 which increases metabolism and body temperature. Your Reverse T3 and your T3 are usually in direct relation to each other; if one is high the other is low. Hypos tend to have low FT3, and thus a slowed metabolism.