The thyroid is a small, butterfly-shaped gland in your neck that produces hormones controlling how fast your body uses energy. You can't see it from the outside, but you can sometimes feel it if you gently touch the front of your neck just below your Adam's apple.

Think of your thyroid as your body's thermostat and engine controller combined. It releases chemical messengers called hormones that travel through your bloodstream, telling your cells how quickly to work. When your thyroid produces the right amount of hormones, your heart beats at a normal pace, you maintain a healthy body temperature, and you have steady energy levels. If it produces too much, you might feel jittery, anxious, and overheated, like your body is racing. If it produces too little, you might feel sluggish, cold, and tired, like everything's moving in slow motion.

Doctors can check if someone's thyroid is working properly with a simple blood test. Some people need to take medicine to help their thyroid function correctly. The thyroid needs a mineral called iodine to make its hormones, which is why table salt often has iodine added to it.