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Am Fam Physician. 2017;95(11):online

See related article on subclinical hyperthyroidism.

What is subclinical hyperthyroidism?

The thyroid gland is located in the front of your neck. It makes hormones that tell your body how to use energy. Hyperthyroidism happens when there is too much thyroid hormone in the body. This speeds up your body functions. Subclinical hyperthyroidism is a mild form of hyperthyroidism. Subclinical means that you do not have any symptoms, or that your symptoms are mild.

What causes it?

Several things can cause your body to have too much thyroid hormone. Your thyroid gland may be making too much. A virus can temporarily increase thyroid hormone levels. Taking too much thyroid medicine or getting too much iodine in certain medicines can cause subclinical hyperthyroidism. Some people have benign (not cancer) growths on their thyroid that can make too much thyroid hormone. These are called toxic nodular goiters.

Who gets it?

Only about three people out of 100 have subclinical hyperthyroidism. It is more common in older adults and in people who live in areas where there is not enough iodine in the food.

What are the symptoms?

People with subclinical hyperthyroidism usually do not have any symptoms. If you do have symptoms, they may include:

  • Frequent bowel movements

  • Feeling tired

  • Feeling nervous

  • Unable to tolerate heat

  • Increased sweating

  • Increased appetite

  • Racing heart

  • Losing weight without trying

  • Hair loss

  • Shaking hands

  • Lack of menstrual periods in women

  • Sleep problems

The more symptoms you have, or the worse they are, the more likely you are to have hyperthyroidism.

What problems can it cause?

People older than 65 years who have subclinical hyperthyroidism have a higher risk of a type of irregular heartbeat called atrial fibrillation (AY-tree-ul fibrill-AY-shun). Women who have gone through menopause and who have subclinical hyperthyroidism may have more bone loss than other women.

Should I be tested for it?

Most doctors do not test patients for subclinical hyperthyroidism unless they have symptoms. It's not clear whether treating it will improve your health.

Where can I get more information?

Your doctor

AAFP's Patient Information Resource

American Association of Clinical Endocrinologists

American Thyroid Association

Endocrine Society (Hormone Health Network)

National Institutes of Health

National Library of Medicine

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