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Background
This study aimed to examine the associations of thyroid hormone sensitivity indices, including free triiodothyronine-to-free thyroxine (FT3/FT4) ratio, thyroid feedback quantile-based index by FT4 (TFQIFT4), thyroid-stimulating hormone index (TSHI), and thyrotrophic thyroxine resistance index (TT4RI) with all-cause mortality in euthyroid adults.
Methods
The study included 6243 euthyroid adults from the National Health and Nutrition Examination Survey (NHANES) 2007–2012. FT3/FT4 ratio, TFQIFT4, TSHI, and TT4RI were calculated. The multivariable Cox proportional hazard regression, restricted cubic spline (RCS), and subgroup analysis were conducted.
Results
Individuals in fourth quartile (Q4) had lower all-cause mortality than those in first quartile (Q1) of FT3/FT4 ratio (hazard ratio (HR): 0.70, 95% CI: 0.51, 0.94). Regarding TFQIFT4, individuals in Q4 of TFQIFT4 had a 43% higher all-cause mortality than those in Q1 (HR: 1.43, 95% CI: 1.05, 1.96) (P < 0.05, all). Compared with participants in Q1, no associations of TSHI and TT4RI with mortality were found. TFQIFT4 was linearly and positively associated with mortality. However, the FT3/FT4 ratio showed a U-shaped association with mortality.
Conclusions
Increased risk for all-cause mortality was positively associated with TFQIFT4, suggesting that increased risk for all-cause mortality was associated with decreased central sensitivity to thyroid hormones. Furthermore, the FT3/FT4 ratio showed a U-shaped association with mortality, with an inflection point at 0.5. However, more cohort studies are needed to validate the conclusions.
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German Centre for Cardiovascular Research (DZHK), partner site Greifswald, Greifswald, Germany
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German Centre for Cardiovascular Research (DZHK), partner site Greifswald, Greifswald, Germany
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Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Greifswald, Germany
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Charité – Universitätsmedizin Berlin, BCRT – Berlin Institute of Health Center for Regenerative Therapies, Berlin, Germany
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Institute for Community Medicine, University Medicine Greifswald, Greifswald, Germany
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Objective
Thyroid dysfunction is associated with relevant disturbances in glucose metabolism. Moreover, thyroid function undergoes important changes with ageing. The objective of this study was to investigate the association of thyroid function with insulin resistance with particular consideration of possible age-related effect modifications.
Design
A sample of 4193 participants from two independent epidemiological studies, the Study of Health in Pomerania-TREND-0 and the Berlin Aging Study II, was included in this cross-sectional analysis.
Methods
Insulin resistance was estimated by homeostasis model of insulin resistance (HOMA-IR) and the insulin sensitivity index (ISI). Associations of thyroid biomarkers (thyroid-stimulating hormone, free thyroxine, and free triiodothyronine (fT3)) with parameters of glucose metabolism were analysed by regression models adjusted for age, sex, smoking status, and study site.
Results
A higher fT3 was significantly associated with higher fasting glucose and higher fasting and 2-h postload insulin levels, a higher HOMA-IR, and lower ISI. A higher fT3 was also associated with a higher risk for impaired fasting glucose (RR 1.09, 95 CI 1.02; 1.18; P = 0.017). Many of these associations between thyroid markers and parameters of glucose metabolism were significant in young and middle-aged participants but not in older individuals.
Conclusions
The main finding of this study was a consistent association of fT3 with almost all markers of insulin resistance. However, this effect seems to be wearing off in higher age highlighting a potential age-related modification of the interaction between thyroid function and glucose metabolism. Further studies are needed to clarify causal relationships.
Department of Endocrinology, Gateshead Health NHS Foundation Trust, Gateshead, UK
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Department of Cardiology, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK
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Department of Cardiology, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK
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Objectives
To study the relationship between serum-free T3 (FT3), C-reactive protein (CRP) and all-cause mortality in patients with acute myocardial infarction (AMI).
Design
Prospective multicentre longitudinal cohort study.
Methods
Between December 2014 and December 2016, thyroid function and CRP were analysed in AMI (both ST-elevation (STEMI) and non-ST-elevation) patients from the Thyroxine in Acute Myocardial Infarction study. The relationship of FT3 and CRP at baseline with all-cause mortality up to June 2020 was assessed. Mediation analysis was performed to evaluate if CRP mediated the relationship between FT3 and mortality.
Results
In 1919 AMI patients (29.2% women, mean (s.d.) age: 64.2 (12.1) years and 48.7% STEMI) followed over a median (interquartile range) period of 51 (46–58) months, there were 277 (14.4%) deaths. Overall, lower serum FT3 and higher CRP levels were associated with higher risk of mortality. When divided the patients into tertiles based on the levels of FT3 and CRP; the group with the lowest FT3 and highest CRP levels had a 2.5-fold increase in mortality risk (adjusted hazard ratio (95% CI) of 2.48 (1.82–3.16)) compared to the group with the highest FT3 and lowest CRP values. CRP mediated 9.8% (95% CI: 6.1–15.0%) of the relationship between FT3 and mortality.
Conclusions
In AMI patients, lower serum FT3 levels on admission are associated with a higher mortality risk, which is partly mediated by inflammation. Adequately designed trials to explore the potential benefits of T3 in AMI patients are required.
