Lower free triiodothyronine levels are associated with higher all-cause and cardiovascular mortality in people with diabetes-NHANES 2007–2012

Thyroid hormone plays a key role in maintaining cardiovascular system homeostasis. However, there is limited evidence regarding the correlation between normal range thyroid hormone levels and all-cause mortality or cardiovascular mortality among individuals with diabetes.This retrospective study analyzed data from 1,208 individuals with diabetes who participated in the National Health and Nutrition Survey (NHANES) conducted in the United States between 2007 and 2012. Weighted Kaplan-Meier (KM) analysis and Cox proportional hazards models were used to explore the association between thyroid hormone indices and mortality.The Weighted Kaplan-Meier (KM) analysis revealed statistically significant differences in survival probabilities across free triiodothyronine (FT3), free thyroxine (FT4), FT3/FT4 ratio and thyroid-stimulating hormone (TSH) groups (p < 0.05 or < 0.001). In the multivariate adjusted Cox proportional hazards models, higher levels of FT3 were founded to be associated with decreased all-cause mortality (HR (95% CI), 0.715 (0.567, 0.900)), cardio-cerebrovascular mortality (0.576 (0.408, 0.814)) and cardiovascular mortality (0.629 (0.438, 0.904)). Notably, this correlation was more significant among individuals over the age of 60, as indicated by the results of the nonlinear regression analysis.FT3 is an independent predictor of all-cause death, cardio-cerebrovascular and cardiovascular death in euthyroid subjects with diabetes.