Normal-range thyroid-stimulating hormone levels and cardiovascular events and mortality in type 2 diabetes

Aims: Thyroid dysfunction is a risk factor for cardiovascular disease. Whether thyroid function within the normal range is a risk factor for cardiovascular disease remains uncertain. The aim of this study is to evaluate whether plasma thyroid-stimulating hormone (TSH) levels in the normal range are a risk factor for cardiovascular disease and mortality in participants with type 2 diabetes mellitus with high cardiovascular risk. Methods: We included 1265 participants with high cardiovascular risk, type 2 diabetes, and TSH within the normal range (0.35–5.00 mIU/L) from the Second Manifestations of ARTerial disease cohort. The primary outcome was major cardiovascular events (MACE; vascular death, stroke and myocardial infarction). Secondary outcomes of interest were the separate vascular outcomes and all-cause mortality. Cox proportional hazard models were used to evaluate the risk of plasma TSH levels on all outcomes. Results: A total of 191 MACE occurred during a total follow-up of 8183 years. Plasma TSH levels were not associated with MACE (hazard ratio (HR) per mIU/L TSH increase 0.93; 95% confidence interval (95%CI) 0.80–1.08). With a total of 54 strokes during the study period, plasma TSH was associated with a lower risk of stroke (HR per mIU/L 0.64, 95% CI 0.45–0.89). There was no association between plasma TSH levels and risk of myocardial infarction, vascular death, or all-cause mortality. Conclusions: Higher TSH levels within the normal range are associated with a lower risk of stroke in high-risk patients with type 2 diabetes, but not associated with the risk of other cardiovascular events or mortality.