Subclinical hypothyroidism is associated
with an increased risk of coronary heart disease
(March 2006)
The background of the study. Thyroid dysfunction,
particularly subclinical thyroid dysfunction (low or high serum
thyrotropin [TSH] and normal free thyroxine [T4] concentrations),
may be a risk factor for cardiovascular diseases. In this study,
the frequency of coronary heart disease was determined in euthyroid
subjects and subjects with subclinical hypothyroidism or subclinical
hyperthyroidism.
How the study was done. The study subjects were
2064 subjects (mean age, 50 years) living in a rural town in Western
Australia. They were enrolled in 1981, at which time they completed
health questionnaires and had an electrocardiogram and measurements
of serum TSH and free T4. Coronary heart disease was diagnosed on
the basis of history and electrocardiography. The morbidity and
mortality from coronary heart disease and cardiovascular disease
in general through 2001 was determined by review of the death and
hospital records.
The results of the study. In 1981, 119 subjects
(6 percent) had subclinical hypothyroidism, 1906 (92 percent) had
normal serum TSH concentrations, and 39 (2 percent) had subclinical
hyperthyroidism. Coronary heart disease was more common in the subjects
with subclinical hypothyroidism (15 percent), but not in those with
subclinical hyperthyroidism (5 percent), as compared with the euthyroid
subjects (8 percent).
Among the 1890 subjects who did not have coronary heart disease
in 1981, the risk of fatal and nonfatal coronary heart disease during
follow-up was higher in the subjects with subclinical hypothyroidism
than in the euthyroid subjects (hazard ratio, 1.5), but not in the
subjects with subclinical hyperthyroidism. The death rate from cardiovascular
disease during follow-up was similar in the three groups.
The conclusions of the study. Coronary heart disease
is more common in subjects with subclinical hypothyroidism than
in those with normal serum TSH values, but is not more common in
subjects with subclinical hyperthyroidism.
The original article. Walsh JP, Bremner AP, Bulsara
MK, O’Leary P, Leedman PJ, Feddema P, Michelangeli V. Subclinical
thyroid dysfunction as a risk factor for cardiovascular disease.
Arch Intern Med 2005;165:2467-72.
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