The thyroid's function is to regulate the metabolism of the body. How fast things go, or how slow things go. It does everything from the top of the head, all the way to the toes, in regard to how fine your hair is, how coarse your hair is. How fine or coarse your skin is, if you have diarrhea, or constipation on the extremes. It also will regulate your weight. If you're a fast metabolizer where you're burning calories, or if you're a slow metabolizer where you're going to gain weight. It also can affect your heartbeat, in terms of how fast or how slow it goes.