He wonders if the tests are wrong and feels he should be taking more thyroid hormone. Although Mrs. Smith and Mr. Jones are fictitious, they are typical of many patients that are referred to endocrinologists. Fatigue and weight gain are two of the most common symptoms that bring people to see their family doctor. Before we try to answer these questions it would be best to review the role of the thyroid and the tests we use to determine if the thyroid is functioning normally. The thyroid gland's role in the body is very similar to cruise control in the car.
Cruise control keeps a car running at a constant steady speed.
When we do not want to worry about having to keep a steady foot on the accelerator we turn on cruise control and the car maintains a normal speed without any effort. Thyroid hormone keeps the rest of the body working at the right speed. If thyroid hormone levels decrease, cells throughout the rest of the body decrease in activity. As a result the cells need less energy and thus more energy is available to be stored and the weight increases even though the appetite decreases. Less heat is produced, the person becomes cold, and the sweat glands do not keep the skin moist anymore.