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The thyroid gland, located in the neck just below the Adam's apple,
produces hormones that increase the body's metabolic rate. Both an underactive
thyroid (a condition called hypothyroidism) and an overactive thyroid
(hyperthyroidism) can have serious health consequences.
The study investigators, led by Dr. E. Chester Ridgway, head of the
division of endocrinology, metabolism and diabetes at the University
of Colorado Health Science Center in Denver, are calling for more widespread
testing and more aggressive treatment for thyroid conditions. Their
report appears in the February 28 issue of the Archives of Internal
Medicine.
In studying data from 25,862 adult patients in the general Oregon population,
they found that 9.5 percent had hypothyroidism and 2.2 percent had hyperthyroidism.
Most people with hypothyroidism (8.9 of the 9.5 percent) were not taking
medication for their condition, the researchers found. Half of those
with hyperthyroidism (1.1 of the 2.2 percent) were not being treated.
Therefore, they determined that almost 10 percent of the population
may have a thyroid condition that is either untreated or undiagnosed.
The researchers obtained their data from the statewide health symposium
in Colorado. This program collects population information about various
health conditions such as high blood pressure, cancer and, beginning
in 1995, thyroid problems. During the symposium, physicians surveyed
the participants about possible thyroid symptoms and drew blood to determine
thyroid stimulating hormone (TSH) levels.
The thyroid is controlled in part by the pituitary gland in the brain,
which releases TSH. This pituitary hormone stimulates the thyroid to
release its own hormones. When enough thyroid hormones are in the blood,
the pituitary releases less TSH. When more thyroid hormone is needed,
the pituitary releases more TSH. Therefore, low TSH levels are indicative
of hyperthyroidism, and high TSH indicates hypothyroidism.
Ridgway explained that in addition to high TSH levels, overt hypothyroidism
is characterized by low amounts of circulating thyroid hormone. Subclinical
hypothyroidism entails having high TSH but normal levels of circulating
thyroid hormone. The symptoms of subclinical hypothyroidism are fatigue,
mild weight gain, constipation, dry skin and increased sleeping. These
can often be confused with symptoms of other conditions.
In the study, the researchers also found that those with overt hypothyroidism
had total cholesterol levels of 251 milligrams per deciliter. (Total
cholesterol above 200 milligrams per deciliter indicates that medical
attention is needed.) People with subclinical hypothyroidism had total
cholesterol levels averaging 224 milligrams per deciliter.
Though physicians have known that overt hyperthyroidism plays a role
in increased cholesterol levels, not as much has been reported about
how subclinical hypothyroidism contributes to cholesterol levels.
``This study is novel in that is drew a clearer connection between mild
or early stages of thyroid failure and its effect on cholesterol levels,''
Ridgway said. ``It showed that as the thyroid gland fails and less thyroid
hormone is produced, blood cholesterol levels rise. This has serious
long-term consequences for the patient's health particularly in the
area of cardiovascular disease.''
Subclinical hypothyroidism ``may not be subclinical at all,'' said Paul
W. Ladenson, professor of medicine and director of the division of endocrinology
and metabolism at the Johns Hopkins University of Medicine. ``But rather,
mild degrees of thyroid hormone deficiency may have significant consequences
in terms of higher cholesterol, greater risk of heart disease, as well
as symptoms that can progress to more severe hypothyroidism.''
``In a sense, the term subclinical is a misnomer,'' Rigdway concurred.
``One of the most important parts of our study was to show that these
patients do have symptoms, and in fact this disorder subclinical hypothyroidism
actually has elevated cholesterol levels compared with normal controls.''
Ladenson also explained that the American Thyroid Association (www.thyroid.org)
recently released a set of guidelines stating people over 35 years old
should be screened with TSH tests every five years.
Archives of Internal Medicine (2000;160)
(The Medical Tribune Web site is at http://www.medtrib.com
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