Chinese Association of Idaho State University (CAISU)
If you don't have a thyroid problem, you probably don't spend a lot of time thinking about that butterfly-shaped gland in your neck, which helps regulate metabolism and body temperature (among other things). But thyroid disorders are pretty common—some experts believe 30% of women will develop one in their lifetime. An autoimmune disorder can throw your gland out of whack, but it's thought that lifestyle factors (like stress or diet) also can play a role. Hyperthyroidism (aka an overactive thyroid) can cause rapid weight loss, an unusually fast heartbeat, and anxiety; while hypothyroidism (an underactive thyroid) can trigger constipation, weight gain, and extreme fatigue.