Subclinical hypothyroidism and subclinical
hyperthyroidism have few deleterious cardiovascular effects
(July 2006)
The background of the study. Subclinical thyroid
dysfunction (high or low serum thyrotropin [TSH] and normal serum
free thyroxine [T4] concentrations) may be associated with increases
in cardiovascular morbidity and mortality. In this study, the incidence
of cardiovascular mortality and overall (all-causes) mortality was
determined in a group of older women and men in whom thyroid function
was assessed at base line.
How the study was done. The study subjects were
3233 subjects (1926 women, 1307 men) aged  65 years enrolled
between 1989 and 1993 in a study of risk factors for cardiovascular
disease. At base line, serum TSH was measured in all subjects, and
serum free T4 was measured in those with high or low serum TSH concentrations.
The subjects were categorized into four groups: subclinical hyperthyroidism,
low serum TSH–normal free T4; euthyroid; normal serum TSH;
subclinical hypothyroidism, high serum TSH–normal free T4;
and overt hypothyroidism, high serum TSH–low free T4.
Cardiovascular diseases were determined by self-report and review
of medical records at base line and twice yearly thereafter. Cardiovascular
death and death from other causes were determined from medical records,
autopsy reports, and death certificates.
The results of the study. When evaluated initially,
2639 subjects (82 percent) were euthyroid, 47 (1 percent) had subclinical
hyperthyroidism, 496 (15 percent) subclinical hypothyroidism, and
51 (2 percent) overt hypothyroidism. There were no differences in
the frequency of atrial fibrillation, coronary heart disease, or
cerebrovascular disease in the four groups at that time.
During a mean follow-up period of 12.5 years, atrial fibrillation
occurred slightly more often in the subjects with subclinical hyperthyroidism
than in the euthyroid subjects. There were no differences in the
incidence of coronary heart disease or cerebrovascular disease or
cardiovascular or all-cause mortality in the four groups.
The conclusions of the study. Among older subjects,
the risk of cardiovascular disease or cardiovascular or all-cause
mortality is not increased in those with subclinical hyperthyroidism
or subclinical or overt hypothyroidism, but the risk of atrial fibrillation
is increased in those with subclinical hyperthyroidism.
The original article. Cappola AR, Fried LP, Arnold
AM, Danese MD, Kuller LH, Burke GL, Tracy RP, Ladenson PW. Thyroid
status, cardiovascular risk, and mortality in older adults. JAMA
2006;295:1033-41.
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