Overactive Thyroid Not Your Heart's Friend

Hyperthyroidism associated with increased risk of developing atrial fibrillation

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) An overactive thyroid may affect more than the body's metabolism. It also appears to be associated with a small increased risk of developing a common heart arrhythmia called atrial fibrillation.

Hyperthyroidism, commonly called overactive thyroid, occurs when the thyroid gland makes too much thyroid hormone, speeding up the body's functions. Symptoms include fatigue, difficulty concentrating, increased sweating, larger appetite and weight loss.

These researchers said patients with an underactive thyroid were found to have a lower risk of developing atrial fibrillation.

"Ask your doctor about screening options."

Christian Selmer, MD, a research fellow at Gentofte University Hospital in Copenhagen, Denmark, discovered an association not just between hyperthyroidism and atrial fibrillation, but also in slightly elevated thyroid and the risk of developing the arrhythmia. The study also found that a lower thyroid activity may offer the heart protection against developing the heart arrhythmia. Despite the findings, researchers stress that a direct cause and effect relationship could not be proved.

Previous research has demonstrated that hyperthyroidism is associated with an increased risk of the heart arrhythmia as compared to individuals with normal thyroid function, but it was unclear whether slightly overactive thyroid glands prompted the same risk. There also is little research available regarding arrhythmia risks in patients with underactive thyroid.

During the study, researchers used a nationwide Danish registry to study 586,460 patients who received a thyroid function blood test for the first time from a Copenhagen doctor between 2000 and 2010. Of the participants, 39 percent were men and the average age was 50.

This blood test reveals the amount of thyroid-stimulating hormone in the blood. It is typically high among those with hyperthyroidism and low in patients with an underactive thyroid.

After an average follow up of five and a half years, 17,154 patients, or 3 percent, had developed atrial fibrillation. Just over half of those who developed the heart rhythm disorder were women.

As compared to patients with a normally functioning thyroid, atrial fibrillation risk increased as levels of thyroid-stimulating hormone decreased. Patients with a slightly overactive thyroid were found to have a 30 percent increased risk of atrial fibrillation, while individuals with a high-normal thyroid had a 12 percent increased risk.

In addition, researchers found that thyroid dysfunction was highest among the younger patients and lower in elderly participants. This is because atrial fibrillation in older patients is less often attributed to a thyroid problem, while it is often the main cause of an arrhythmia in younger adults.

Investigators said the findings support long-term atrial fibrillation screenings for patients with thyroid disease. The study was recently published in the British Medical Journal.

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Review Date: 
December 6, 2012
Last Updated:
December 10, 2012