Purpose: Thyroid dysfunction may affect the risk of cardiovascular disease and mortality through effects on myocardial and vascular tissue and metabolism. Levels of thyroid stimulating hormone (TSH) indicates thyroid function. We aimed to assess the association between TSH-levels and incident ischemic heart disease (IHD), incident stroke, and all-cause mortality.
Methods: We included 13,865 participants (18-71 years, 51.6% women) from five cohort studies conducted during 1974-2008 were included. TSH was measured at the baseline examination and classified as <0.4; 0.4-2.5 (ref.); 2.5-5.0; 5.0-10, or >10 mU/l. Incident IHD, incident stroke, and all-cause mortality were identified in registries until ultimo 2013. Data were analysed by multivariate Cox regression with age as underlying time axis. Results from the individual cohorts were pooled by random-effects meta-analysis.
Results: The crude incidence rate was for IHD 7.8 cases/1000 person years (PY); stroke 5.4 cases/1000 PY; and all-cause mortality 11.3 deaths/1000 PY (mean follow-up: 14 years). Analyses showed no statistically significant associations between TSH-levels and incident IHD or incident stroke in the partly or fully adjusted models. There was a statistically significant association between TSH of 2.5-5 mU/l and all-cause mortality (hazard ratio 1.145 (95% CI 1.004-1.306) compared with TSH of 0.4-2.5 mU/l in the fully adjusted model.
Conclusion: The results do not provide evidence of a harmful effect of decreased or increased TSH on IHD or stroke in the general population. However, there is some indication of an elevated risk for all-cause mortality with TSH 2.5-5 mU/l compared with 0.4-2.5 mU/l.
Keywords: Epidemiology; Ischemic heart disease; Mortality; Stroke; Thyrotropin.