DAN Medical Frequently Asked Questions

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Thyroid Conditions

I'd like to learn to dive, but am concerned about my hyperthyroidism. What can you tell me?

Condition: The thyroid is a vital gland that secretes a hormone (thyroxin) that helps regulate body metabolism. In excess quantities (called hyperthyroidism), it can:


  • increase the heart rate,
  • produce cardiac problems,
  • affect respiratory rate,
  • decrease body weight and
  • interact with the central nervous system.


Symptoms of hyperthyroidism also include discomfort or anxiety. Cardiac effects include tachycardia (a fast heartbeat), serious dysrhythmias and heart failure. Hyperthyroidism can cause muscular weakness and periodic paralysis.

Lower-than-normal levels of thyroxin (called hypothyroidism) may cause fatigue as well as slow or absent reflexes. Hypothyroidism is also characterized by a slow heart rate and slow metabolism. It may even cause heart failure.

The thyroid gland's output can be controlled by medication, radiation, radioactive iodine or surgery. This helps to reduce the function of the thyroid, or it can diminish the amount of hormone released. Once the hormone level has been reduced to within normal range (assessed by blood tests), and the signs and symptoms of hyperthyroidism have resolved, then a diver with a thyroid condition may resume diving.

Note: This assessment assumes, however, that the diver has no other major health problems and can achieve a suitable level of physical performance. Individuals who are treated by medication, radiation, radioactive iodine or surgery may become truly hypothyroid (have reduced thyroid function) and may require supplemental thyroxine (Synthroid®) to actually raise their hormone level back into the normal range.

Fitness and Diving: Participation in recreational scuba diving is usually considered unsafe for an individual with active hyperthyroidism or hypothyroidism. In untreated hyperthyroidism, thyroid hormone can sometimes be suddenly released in large quantities, which could cause debilitating symptoms for a submerged diver.

After treatment of hyperthyroidism, thyroid hormone levels often drop below normal (hypothyroidism), but the missing hormone can easily be replaced with a synthetic substitute, Synthroid, restoring thyroid hormone levels in the blood to normal.

Divers with a history of thyroid disease should have their cardiovascular system critically assessed and have had their thyroid function checked within the previous three months prior to diving. Synthroid, the medication often used in treatment, has no known interaction with nitrogen.

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