Thyroid Research Thyroid Research Archive Thyroid Disease
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.