Overactive Thyroid Tied to Irregular Heart Rhythm

But other heart problems aren't linked to trouble with the gland, study suggests

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By Steven Reinberg
HealthDay Reporter

TUESDAY, Feb. 28, 2006 (HealthDay News) -- Having an overactive thyroid gland, with no symptoms of thyroid disease, is associated with an increased risk for atrial fibrillation -- an abnormal heart rhythm.

But, an overactive or underactive thyroid is not linked with a higher risk for other heart problems or an increased risk of death, researchers report.

The thyroid and its hormones play an important role in regulating the body's metabolism and calcium balance. And while thyroid problems are common, they are easily diagnosed and treated.

It has been thought that abnormal levels of thyroid stimulating hormone (TSH) may be a risk factor for heart disease. But this new study found no such association for asymptomatic thyroid problems in older patients.

The findings suggest that people don't have to be screened for abnormal levels of TSH or treated for an over- or underactive thyroid if they have no symptoms of trouble.

The finding appears in the March 1 issue of the Journal of the American Medical Association.

"People who have subclinical underactive thyroid do not have an increased risk of cardiovascular disease, like heart attack or stroke or mortality compared with people who have normal thyroid function," said study lead author Dr. Anne R. Cappola, an assistant professor of medicine and epidemiology at the University of Pennsylvania School of Medicine.

"However, people who have subclinical overactive thyroid do have an increased risk of atrial fibrillation," she added.

In their study, Cappola and her colleagues collected data on 3,233 people aged 65 years or older who had their TSH levels measured in 1989 and 1990. Through June 2002, 82 percent of the people had normal thyroid function, 15 percent had subclinical underactive thyroid, 1.6 percent had a symptomatic underactive thyroid, and 1.5 percent had subclinical overactive thyroid, the researchers found.

Cappola's team also found that people with a subclinical overactive thyroid had almost twice the risk of developing atrial fibrillation, compared with those with a normal thyroid.

However, there was no increased risk for coronary heart disease, stroke, or death. Also, for those with an under-active thyroid, there were no differences from people with normal thyroid function for heart disease, stroke, or death, the researchers found.

"If someone has subclinical overactive thyroid they should be treated to prevent atrial fibrillation," Cappola said. "For those who have a mild underactive thyroid, they may not need to be treated," she added.

Many older people are being treated for an underactive thyroid in the belief that treatment will prevent heart problems, Cappola said. "We don't see any evidence that treatment is going to help the heart," she said.

Cappola doesn't think patients with an asymptomatic underactive thyroid need to be treated. "They need to have a discussion with their doctor," she said. In addition, she doesn't think it is necessary for older people to be screened for thyroid problems, since it is neither cost-effective nor likely to make a difference to the patient's health.

One expert agrees that the current practice of treating subclinical thyroid problems is unnecessary.

"This is going against what people have been thinking," said Dr. Robert Rushakoff, an associate clinical professor of medicine at the University of California, San Francisco. "When you actually look at the data, suddenly the answers are different from what people have thought."

Rushakoff doesn't think the risk of atrial fibrillation is as great as the study suggests, and that patients with an asymptomatic overactive thyroid may not need treatment. "The numbers of people affected are small," he said. "There are also risks to treatment. The benefit of treatment may outweigh the risks."

"If there is no clinical issue you don't need treatment," Rushakoff added. "The evidence is pointing to that. Also, you do not need to be screened for thyroid disease. It's against all the recommendations right now, but that's where it's going."

More information

The American Academy of Otolaryngology, Head and Neck Surgery can tell you more about thyroid disease.

SOURCES: Anne R. Cappola, M.D., Sc.M., assistant professor, medicine and epidemiology, University of Pennsylvania School of Medicine, Philadelphia; Robert Rushakoff, M.D., associate clinical professor, medicine, University of California, San Francisco; March 1, 2006, Journal of the American Medical Association

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