People who have an overactive thyroid gland, but no symptoms of thyroid disease, are at an increased risk of atria fibrillation, an abnormal heart rhythm, according to a recent study. But contrary to standard scientific thinking, the study found that an overactive or underactive thyroid is not linked to an increased risk of other heart problems or death in older patients.
In the study, researchers collected data on 3,233 people ages 65 and older who had their thyroid stimulating hormone (TSH) levels measured in 1989 and 1990. Through June 2002, 82% of the people maintained normal thyroid function, 15% had a subclinical underactive thyroid, 1.6% had a symptomatic underactive thyroid and 1.5% had a subclinical overactive thyroid, according to the researchers.
People who had a subclinical overactive thyroid had almost twice the risk of developing atrial fibrillation, compared with those who had a normal thyroid. However, there was no increased risk for coronary heart disease, stroke or death.
There was no difference in the risk of heart disease, stroke or death between the people who had an underactive thyroid and those who had normal thyroid
"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," says lead author of the study, 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. They should be treated to prevent it," she says.
Dr. Robert Rushakoff, an associate clinical professor of medicine at the University of California, San Francisco, thinks that the risk of atrial fibrillation is not as great as the study suggests, and therefore, feels that even patients who have a subclinical overactive thyroid may not need treatment. "If there is no clinical issue, you don't need treatment," he says. "The evidence is pointing to that. There are also risks to treatment."
Many older people are being treated for an asymptomatic underactive thyroid in the belief that treatment will prevent heart problems, Cappola says. She thinks that's unnecessary. "We don't see any evidence that treatment is going to help the heart," she says.
In addition, Cappola believes older people do not even need to be screened for thyroid problems, since it is neither cost-effective nor likely to make a difference to their health.
"This is going against what people have been thinking," says Rushakoff. "'When you actually look at the data, suddenly the answers are different from what people have thought. It's against all the recommendations right now, but that's where it's going."