The thyroid -- a butterfly-shaped gland in the front of your neck -- makes hormones that control the way your body uses energy. Your thyroid controls your metabolism, which is how your body turns food into energy, and also affects your heart, muscles, bones, and cholesterol.
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While thyroid disorders can range from a small, harmless goiter (enlarged gland) to life-threatening cancer, the most common thyroid problems involve an abnormal production of thyroid hormones. If there is too much of these vital body chemicals, the result is a condition known as hyperthyroidism. Too little hormone production leads to hypothyroidism.
Although the effects of thyroid problems are unpleasant or uncomfortable, most thyroid conditions can be managed well if properly diagnosed and treated.
What Is an Overactive Thyroid?
Hyperthyroidism happens when the thyroid becomes overactive and produces too much of its hormones. Hyperthyroidism affects women five times to 10 times more often than men, and is most common in people younger than 40. People with hyperthyroidism have problems that reflect over activity of the body's organs, resulting in such symptoms as sweating, feeling hot, rapid heartbeat, weight loss, and sometimes eye problems.
Hyperthyroidism can occur in several ways:
Graves' disease: The release of excess hormones is triggered by an autoimmune disorder. For some unknown reason, the body attacks the thyroid, causing it to spill out too much hormone.
Toxic adenomas: Nodules (abnormal growths or lumps) develop in the thyroid gland and begin to secrete thyroid hormones, upsetting the body's chemical balance. Some goiters may contain several of these nodules.
Subacute thyroiditis: Painful inflammation of the thyroid causes the gland to enlarge and "leak" excess hormones, resulting in temporary hyperthyroidism, which resolves spontaneously. Subacute thyroiditis generally lasts a few weeks but may persist for months.
Pituitary gland malfunctions or cancerous growths in the thyroid gland: Although rare, hyperthyroidism can also develop from these causes.
Silent thyroiditis: This is usually a temporary state of excess thyroid hormone release causing mild hyperthyroidism. In some cases it can result in permanent damage to the thyroid and low thyroid hormone production by the gland.
Postpartum thyroiditis: This is a type of hyperthyroidism that occurs in a small percentage of women within months of delivery. It last only a few months, followed by several months of reduced amounts of thyroid hormone production by the gland. Typically these women fully recover normal thyroid function.
Ingestion of excess thyroid hormone can result in hyperthyroidism.
What Is an Underactive Thyroid?
Hypothyroidism, by contrast, stems from an underproduction of thyroid hormones. Since your body's energy production requires certain amounts of thyroid hormones, a drop in hormone production leads to lower energy levels, causing you to feel weak and tired.