Prediction of all-cause and cardiovascular mortality in elderly people from one low serum thyrotropin result: a 10-year cohort study

Background Low serum thyrotropin, in combination with normal concentrations of circulating thyroid hormones, is common, especially in elderly people a nd in individuals with a history of thyroid disease. We aimed to assess the long-term effects of subclinical hyperthyroidism on mortality. Methods We did a population-based study of mortality in a cohort of 1191 in dividuals not on thyroxine or antithyroid medication. All participants were aged 60 years or older. We measured concentration of thyrotropin in serum at baseline in 1988-89. We recorded vital status on June 1, 1999, and ascer tained causes of death for those who had died. We compared data for causes of death with age-specific, sex-specific, and year-specific data for Englan d and Wales. We also compared mortality within the cohort according to init ial thyrotropin measurement. Results During 9733 person-years of follow-up, 509 of 1191 people died, the expected number of deaths being 496 (standardised mortality ratio [SMR] 1. 0, 95% CI 0.9-1.1). Mortality from all causes was significantly increased a t 2 (SMR 2.1), 3 (2.1), 4 (1.7), and 5 (1.8) years after first measurement in those with low serum thyrotropin (n=71). These increases were largely ac counted for by significant increases in mortality due to circulatory diseas es (SMR 2.1, 2.2, 1.9, 2.0, at years 2, 3, 4, and 5 respectively). Increase s in mortality from all causes in years 2-5 were higher in patients with lo w serum thyrotropin than in the rest of the cohort (hazard ratios for years 2, 3, 4, and 5 were 2.1, 2.2, 1.8, and 1.8, respectively). This result ref lects an increase in mortality from circulatory diseases (hazard ratios at years 2, 3, 4, and 5 were 2.3, 2.6, 2.3, 2.3), and specifically from cardio vascular diseases (hazard ratios at years 2, 3, 4, and 5 were 3.3, 3.0, 2.3 , 2.2). Interpretation A single measurement of low serum thyrotropin in individuals aged 60 years or older is associated with increased mortality from all cau ses, and in particular mortality due to circulatory and cardiovascular dise ases.