As part of your endocrine system, the thyroid gland releases hormones into your blood. These hormones act like chemical messengers, influencing many things, including your body's metabolism rate, temperature, muscle strength, cholesterol levels, even your mood. A thyroid gland that releases too little or too much hormone can take a toll on your health. Too much hormone results in hyperthyroidism and produces the opposite effect. An overactive thyroid gland can accelerate your body's metabolism rate by 60 percent to 100 percent, causing sudden weight loss and a host of other symptoms.
Women are much more likely than men to have an overactive thyroid.
The condition is most common in young adulthood and middle age, although it can occur at any age. Hyperthyroidism is usually caused by Graves' disease, a condition where antibodies produced by your immune system can cause the thyroid to increase hormone output. Another but less common cause occurs when a portion of the thyroid gland acts on its own and produces too much thyroid hormone. The most typical symptoms include elevated heart rate, heat intolerance and a tendency during usual activity to become more tired. Your doctor can help you determine an appropriate treatment, depending on your physical condition, age and the severity of your hyperthyroidism.