Penn Study Finds No Increased Cardiovascular
Risk in Patients with Mild Thyroid Underactivity
Researchers at the University of Pennsylvania
School of Medicine have found leaving a mildly
underactive thyroid gland untreated does not lead
to increased cardiovascular risk.
Study results published in the March 1, 2006
issue of the Journal of the American Medical Association,
may lead to changes in the clinical care of this
commonly diagnosed condition.
The thyroid gland, located at the base of the
neck, produces thyroid hormone which acts throughout
the body to regulate metabolism. Patients with
substantial underactivity of the thyroid gland,
or hypothyroidism,
may suffer from a variety of symptoms including:
- fatigue
- constipation
- weight gain
These patients are typically treated with medication
to increase the thyroid hormone in the body. Patients
with an overactive thyroid gland, or hyperthyroidism,
may also be symptomatic and require treatment
to lower their thyroid hormone levels.
Mild thyroid abnormalities are common and are
usually not associated with any symptoms. Whether
or not these mild abnormalities pose a risk to
patients has been a questionable area. Many leading
endocrinologists have advocated treatment of patients
with mild thyroid problems based on the belief
that mild thyroid problems increase cardiovascular
risk.
"Previous studies have suggested that abnormal
levels of thyroid stimulating hormone may represent
a cardiac risk factor, the way that increased
cholesterol or smoking are risk factors for heart
disease," said lead author Anne
Cappola, MD, ScM, Assistant Professor of Medicine
and Epidemiology. “We set out to answer
the question of whether there are cardiovascular
consequences resulting from mild thyroid problems,
using data from a large population studied for
a long period of follow-up.”
Cappola measured thyroid function through a blood
test in 3,200 men and women, aged 65 and older,
who participated in the Cardiovascular Health
Study, a large multi-center cohort study sponsored
by the National Institutes of Health. Study participants
had no reason to have an abnormal thyroid test
at enrollment and were not taking thyroid hormone
replacement. Cappola categorized these patients
into different groups based on their thyroid blood
tests and determined the risk of cardiovascular
problems over 13 years of follow-up.
Patients with a mildly underactive thyroid gland
made up 15 percent of the study, and showed no
elevation in their risk of suffering an arrhythmia,
heart attack, stroke or death. The only group
that experienced adverse cardiac events was a
small fraction of patients (1.5 percent) who had
a mildly overactive thyroid. These patients had
an increased risk of developing common abnormal
heart rhythm, atrial fibrillation, but no other
cardiovascular threats such as heart attacks or
death.
Cappola adds, “It’s our wish to figure
out what is a ‘normal’ versus an ‘abnormal’
thyroid function… which thyroid hormone
levels are associated with the highest level of
physical function and health in the general population.
Many patients with mild thyroid problems are being
treated now and it is not clear if this is actually
helping them. We need to put together a better
understanding of the risks and benefits of treatment
for mild thyroid abnormalities.”
So should general practitioners be screening
patients over a certain age every so often for
thyroid dysfunction?
Some organizations recommend it.
“Based on our findings, we believe there
is no convincing evidence to support screening
for mild thyroid problems in the general population
in patients who have no symptoms. But if you do
find someone over the age of 65 with a mildly
overactive thyroid, our study suggests that they
should be treated,” explains Cappola. “There’s
no evidence you should treat someone with a mildly
underactive thyroid in order to help deter cardiovascular
disease.”
The results of this study are available online
at:
http://jama.ama-assn.org. The article is titled,
“Thyroid Status, Cardiovascular Risk and
Mortality, in Older Adults.”
This study was supported by an American Heart
Association Grand-in-Aid; contracts from the National
Heart, Lung and Blood Institute; and a grant from
the National Institute on Aging.
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