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The findings were scheduled to be presented Thursday at the American Thyroid Association annual meeting in Quebec City, Canada.
A person is considered to have subclinical hyperthyroidism when their blood levels of thyroid-stimulating hormone are low, but levels of the thyroid hormones known as thyroxine and triiodothyronine are normal. In full-blown hyperthyroidism, thyroid hormone levels are high.
"Hyperthyroidism is associated with a number of health concerns, chief among them being cardiovascular disease," Douglas Forrest, of the U.S. National Institute of Diabetes and Digestive and Kidney Diseases and program co-chairman for the meeting, said in an association news release. "Though subclinical hyperthyroidism mimics some of the features of classic hyperthyroidism, new data show that a link to cardiovascular disease is not one of them."
Subclinical hyperthyroidism affects roughly 1 percent to 2 percent of adults aged 65 and older, according to the news release.
Researchers led by Dr. Paige Fortinsky, of the University of Pennsylvania Medical Center in Philadelphia, examined data on more than 5,000 men and women aged 65 and older enrolled in a heart health study who were not taking thyroid medication. They found that 70 of the participants had subclinical hyperthyroidism. The progression of the condition in this group was monitored over the course of two to three years.
Of the 70 people with subclinical hyperthyroidism, 60 percent were women and 24 percent were nonwhite. The average age of the group was about 74.
During the follow-up period, 43 percent of participants with subclinical hyperthyroidism did not have a change in their condition. Meanwhile, 41 percent improved and their thyroid hormone levels returned to normal, 5 percent progressed to hyperthyroidism, and 11 percent starting taking thyroid medication.
The researchers found no link between subclinical hyperthyroidism and death or heart disease.
Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.
-- Mary Elizabeth Dallas
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