New
evidence suggests that a type of overactive thyroid condition appears to boost
the risk of heart problems, especially atrial fibrillation (a form of irregular
heartbeat) and premature death.
Patients sometimes are reluctant to do anything
about the condition, known as subclinical
hyperthyroidism, because it often doesn't cause any symptoms. The findings
show, however, that "physicians and patients should take it seriously and
consider the appropriate way to treat it to prevent increases in heart disease,
bone problems and death," said Dr. Kenneth Burman, chief of the endocrine
section at Washington Hospital Center, in Washington, D.C.
Patients with subclinical hyperthyroidism have
too much of the hormone created by the thyroid gland, which
helps control people's metabolism. An estimated 10 percent of the population
has the condition, which is considered to be less serious than overt
hyperthyroidism.
Researchers have wondered for years whether
subclinical hyperthyroidism puts people at risk of a variety of health
problems. Previous research has suggested it does, and a new study takes a
closer look and finds more reasons to suspect the condition is dangerous.
The report authors examined the results of 10
studies, which included nearly 53,000 participants. After adjusting their
statistics so they wouldn't be skewed by high or low numbers of participants of
certain ages or genders, the researchers found that those with subclinical
hyperthyroidism were 24 percent more likely to die during the study periods, 29
percent more likely to die of heart-related problems and 68 percent more likely
to have atrial fibrillation.
Burman, who wrote a commentary accompanying the study,
said the risk of early death and heart problems were
still low even with the increased risk. The risk of death during the study
period, for example, rose overall from 16 percent in those with normal thyroid
levels to 18 percent in those with subclinical hyperthyroidism. But the
heightened risk of atrial fibrillation was a significant jump, he said. Atrial fibrillation causes
the heart to fail to beat properly, putting patients at higher risk of stroke.
What to do? Physicians often turn to medication
first, then surgery or treatment with radioactive iodine, Burman said. But
medication raises questions, he said: "Do you keep them on medication
indefinitely when they feel fine and the medications have side effects?"
Study co-author Dr. Nicolas Rodondi, head of
ambulatory care at the University of Bern, in Switzerland, said treatment
should be considered if patients are in certain risk groups and only if their
thyroid levels remain abnormal after they're rechecked in three to six months.
The next step in research is to confirm the analysis
findings and explore how treatment may help patients lower their risks of
problems, he said.
The study appears online April 23 in the journal Archives
of Internal Medicine. A second study, also published in the journal,
examined whether the drug levothyroxine sodium -- a man-made form of the
thyroid hormone -- would help reduce the risk of cardiovascular problems in
patients with subclinical hypothyroidism.
The study of about 4,800 patients, led by
researchers at Newcastle University in England, found that the drug (brand
names include Synthroid), appeared to reduce the risk of heart problems in relatively
younger patients (aged 40 to 70) but not in older patients (over 70).
In younger patients, about 4 percent of those
treated with the drug had heart disease, compared with nearly 7 percent of
those who weren't treated with it. After adjusting their statistics so they
wouldn't be skewed by various factors, the researchers found that those who
took the drug had a 39 percent lower risk of heart disease.
The drug can, however, cause a variety of side
effects. Researchers could not definitively explain why older patients didn't
receive the same health benefit.
A co-author for this study has received a speaking
fee from drug manufacturer Merck Serono.
More
information: For details about thyroid
diseases, try the U.S. National Library of Medicine.
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