Your thyroid produces thyroid hormone, which controls many activities in your body, including how fast you burn calories and how fast your heart beats. Diseases of the thyroid cause it to make either too much or too little of the hormone. Depending on how much or how little hormone your thyroid makes, you may often feel restless or tired, or you may lose or gain weight. Women are more likely than men to have thyroid diseases, especially right after pregnancy and after menopause.

Your thyroid is a small butterfly-shaped gland found at the base of your neck, just below your Adam's apple. This gland makes thyroid hormone that travels in your blood to all parts of your body. The thyroid hormone controls your body's metabolism in many ways, including how fast you burn calories and how fast your heart beats.