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Fatigued or full throttle: Is your thyroid to blame?


WebMD Medical Reference
Medically Reviewed by Dr Rob Hicks

The thyroid is like a speed control or accelerator for the body.

An overactive thyroid can leave a person feeling 'revved up', even when they should be getting ready to sleep at bedtime.

An underactive thyroid slows a person down, and may cause symptoms of depression, fatigue, and weight gain. 

Thyroid conditions are relatively common, and can be treated.

What is an overactive thyroid?

Hyperthyroidism happens when the thyroid becomes overactive and produces too much of its hormones. Hyperthyroidism affects women 10 times more often than men, and is most common in people aged 20-40. People with hyperthyroidism have problems that reflect overactivity of the organs of the body, resulting in symptoms such as sweating, feeling hot, rapid heartbeats, 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 goitres 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: 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: A type of hyperthyroidism that occurs in a small percentage of women within months of delivery. It last only a few months, followed by a 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.

Hypothyroidism is more common in women and affects 15 in every 1,000 women and one in 1,000 men in the UK. Hypothyroidism also tends to run in families.

If hypothyroidism is not treated, it can raise your cholesterol levels and make you more likely to have a heart attack or stroke. During pregnancy, untreated hypothyroidism can harm your baby. Luckily, hypothyroidism is easy to treat.

Causes of hypothyroidism may include:

  • Hashimoto's thyroiditis: In this autoimmune disorder, the body attacks thyroid tissue. The tissue eventually dies and stops producing hormones. Other autoimmune disorders occur with this condition and other family members may also be affected by this condition.
  • Removal of the thyroid gland: The thyroid may be surgically removed or chemically destroyed as treatment for hyperthyroidism.
  • Exposure to excessive amounts of iodide: The heart medicine amiodarone may expose you to too much iodine. Radioactive iodine treatment for hyperthyroidism can also result in hypothyroidism. You may be at greater risk of developing hypothyroidism if you have had thyroid problems in the past.
  • Lithium: This drug has also been linked as a cause of hypothyroidism.

If left untreated for a long period of time, hypothyroidism can bring on a myxoedema coma, a rare but potentially fatal condition that requires immediate thyroid hormone replacement usually given intravenously.

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