"It is subclinical in the sense that no one has checked it before, and if you do more screening, the chances are that people will show up in the office with hypothyroidism [low thyroid function]," Newman said.
People with low thyroid function can feel very tired, gain excess weight, have a puffy look and slow down in general, she said, phenomena that are not uncommon among older people.
"The reason we looked at this is that there has been a question about whether you really need to start treatment to replace the thyroid hormone with more modest levels of TSH," Newman said. "We didn't see an increased risk of heart disease with readings under 10."
Treatment of low thyroid function is thyroid replacement hormone, "a single small pill once a day, adjusted to body size and metabolism," she said.
Hypothyroidism can be difficult for a physician to detect unless a screening blood test is done, and that test is not done by many physicians who deal with older people, Newman said.
"I think the rate of hypothyroidism is high enough to make it worth while to screen for it," she said.
This study alone is not enough to support treatment for anyone with a TSH reading of 10 or higher, Cappola said. "We're reluctant to recommend that with an observational study," she said. "But this is, clinically, more evidence that someone with a TSH level 10 or above should be treated."
Learn about thyroid problems and their treatment from the U.S. National Library of Medicine.
SOURCES: Anne R. Cappola, assistant professor, medicine and epidemiology, University of Pennsylvania, Philadelphia; Anne B. Newman, M.D., professor, epidemiology and medicine, University of Pittsburgh; Sept. 23, 2008,
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