Subclinical Thyroid Dysfunction as a Risk Factor for Cardiovascular Disease

TLDR

Few large epidemiological studies have examined the link between thyroid dysfunction and cardiovascular disease, and it remains unclear whether subclinical hypothyroidism is a risk factor. The study aimed to assess the prevalence of coronary heart disease in individuals with subclinical thyroid dysfunction and to evaluate their risk of cardiovascular mortality and events. Researchers measured serum thyrotropin and free thyroxine in 2,108 archived samples from a 1981 community health survey and conducted cross‑sectional and longitudinal analyses to compare coronary heart disease outcomes between those with and without subclinical thyroid dysfunction. Subjects with subclinical hypothyroidism had a significantly higher prevalence of coronary heart disease (OR 1.8) and an elevated risk of cardiovascular death (HR 1.5) and coronary events (HR 1.7), with these associations persisting after adjustment for conventional risk factors, whereas subclinical hyperthyroidism showed no adverse outcomes.

Abstract

There have been few large epidemiological studies examining the association between thyroid dysfunction and cardiovascular disease. In particular, it is uncertain if subclinical hypothyroidism is a risk factor for cardiovascular disease.Serum thyrotropin and free thyroxine concentrations were measured in 2108 archived serum samples from a 1981 community health survey in Busselton, Western Australia (Busselton Health Study). In a cross-sectional study, we examined the prevalence of coronary heart disease in subjects with and without subclinical thyroid dysfunction. In a longitudinal study, we examined the risk of cardiovascular mortality and coronary heart disease events (fatal and nonfatal combined) to the end of 2001 (excluding subjects who had coronary heart disease at baseline).In the cross-sectional analysis, subjects with subclinical hypothyroidism (n = 119) had a significantly higher prevalence of coronary heart disease than euthyroid subjects (n = 1906) (age- and sex-adjusted prevalence odds ratio, 1.8; 95% confidence interval, 1.0-3.1; P = .04). In the longitudinal analysis of subjects with subclinical hypothyroidism (n = 101), there were 21 cardiovascular deaths observed compared with 9.5 expected (age- and sex-adjusted hazard ratio, 1.5; 95% confidence interval, 1.0-2.4; P = .08) and 33 coronary heart disease events observed compared with 14.7 expected (age- and sex-adjusted hazard ratio, 1.7; 95% confidence interval, 1.2-2.4; P < .01). The increased risk of coronary heart disease events remained significant after further adjustment for standard cardiovascular risk factors. Subjects with subclinical hyperthyroidism (n = 39) had no adverse outcomes.Subclinical hypothyroidism may be an independent risk factor for coronary heart disease.