Context: Subclinical thyroid dysfunction is common in older people. However, its clinical importance is uncertain.
Objective: Our objective was to determine the extent to which subclinical hyperthyroidism and hypothyroidism influence the risk of heart failure and cardiovascular diseases in older people.
Setting and design: The Prospective Study of Pravastatin in the Elderly at Risk (PROSPER) is an prospective cohort study.
Patients: Patients included men and women aged 70-82 yr (n=5316) with known cardiovascular risk factors or previous cardiovascular disease.
Main outcome measures: Incidence rate of heart failure hospitalization, atrial fibrillation, and cardiovascular events and mortality according to baseline thyroid status were evaluated. Euthyroid participants (TSH=0.45-4.5 mIU/liter) were compared with those with subclinical hyperthyroidism (TSH<0.45 mIU/liter) and those with subclinical hypothyroidism (TSH≥4.5 mIU/liter, both with normal free T4).
Results: Subclinical hyperthyroidism was present in 71 participants and subclinical hypothyroidism in 199 participants. Over 3.2 yr follow-up, the rate of heart failure was higher for subclinical hyperthyroidism compared with euthyroidism [age- and sex-adjusted hazard ratio (HR)=2.93, 95% confidence interval (CI)=1.37-6.24, P=0.005; multivariate-adjusted HR=3.27, 95% CI=1.52-7.02, P=0.002). Subclinical hypothyroidism (only at threshold>10 mIU/liter) was associated with heart failure (age- and sex-adjusted HR=3.01, 95% CI=1.12-8.11, P=0.029; multivariate HR=2.28, 95% CI=0.84-6.23). There were no strong evidence of an association between subclinical thyroid dysfunction and cardiovascular events or mortality, except in those with TSH below 0.1 or over 10 mIU/liter and not taking pravastatin.
Conclusion: Older people at high cardiovascular risk with low or very high TSH along with normal free T4 appear at increased risk of incident heart failure.