Abstract
CONTEXT: Use of a single set of thyroid function tests to define subclinical hypothyroidism may lead to misclassification over time and could influence findings from longitudinal studies. OBJECTIVE: We assessed the risks of coronary heart disease (CHD), heart failure (HF), and cardiovascular (CV) death in older adults with persistent subclinical hypothyroidism. DESIGN, SETTING, AND PARTICIPANTS: The study included 679 subclinically hypothyroid and 4184 euthyroid U.S. individuals at least 65 yr old enrolled in the Cardiovascular Health Study and not taking thyroid preparations. MAIN OUTCOME MEASURE: We measured the 10-yr risk of incident CHD, HF, and CV death from persistent subclinical hypothyroidism, overall and stratified by degree of TSH elevation (4.5-6.9, 7.0-9.9, and 10.0-19.9 mU/liter). RESULTS: There was no association between persistent subclinical hypothyroidism and incident CHD [hazard ratio (HR), 1.12; 95% confidence interval (CI), 0.93-1.36], HF (HR, 1.05; 95% CI, 0.97-1.27), or CV death (HR, 1.07; 95% CI, 0.87-1.31) in adjusted analyses in which subclinical hypothyroidism was modeled as a time-varying exposure using up to four serial thyroid function tests. When subclinical hypothyroidism was stratified by degree of TSH elevation, no significant associations were found in any stratum. Findings were similar in fixed exposure analyses in which only participants with testing 2 yr apart were considered, with no association between persistent or transient subclinical hypothyroidism and incident CHD, HF, or CV death. CONCLUSIONS: Our data do not support increased risk of CHD, HF, or CV death in older adults with persistent subclinical hypothyroidism.