Association Between Changes in Thyroid Hormones and Incident Type 2 Diabetes: A Seven-Year Longitudinal Study

Update on clinical and experimental management of diabetic cardiomyopathy: addressing current and future therapy

Diabetic cardiomyopathy (DCM) is a severe secondary complication of type 2 diabetes mellitus (T2DM) that is diagnosed as a heart disease occurring in the absence of any previous cardiovascular pathology in diabetic patients. Although it is still lacking an exact definition as it combines aspects of both pathologies - T2DM and heart failure, more evidence comes forward that declares DCM as one complex disease that should be treated separately. It is the ambiguous pathological phenotype, symptoms or biomarkers that makes DCM hard to diagnose and screen for its early onset. This re-view provides an updated look on the novel advances in DCM diagnosis and treatment in the experimental and clinical settings. Management of patients with DCM proposes a challenge by itself and we aim to help navigate and advice clinicians with early screening and pharmacotherapy of DCM.

The association between TSH and thyroid hormones in the normal or subclinical dysfunction range with left ventricular diastolic dysfunction

Thyroid hormones modulate the cardiovascular system. However, the effects of subclinical thyroid dysfunction and euthyroidism on cardiac function remain unclear. We investigated the association between left ventricular (LV) diastolic dysfunction and subclinical thyroid dysfunction or thyroid hormones within the reference range. This cross-sectional study included 26,289 participants (22,197 euthyroid, 3,671 with subclinical hypothyroidism, and 421 with subclinical thyrotoxicosis) who underwent regular health check-ups in the Republic of Korea. Individuals with thyroid stimulating hormone (TSH) levels > 4.2 µIU/mL and normal free thyroxine (FT4, 0.78-1.85 ng/dL) and triiodothyronine (T3, 76-190 ng/dL) levels were defined as having subclinical hypothyroidism. Individuals with serum TSH levels < 0.4 µIU/mL and normal FT4 and T3 levels were defined as having subclinical thyrotoxicosis. The cardiac structure and function were evaluated using echocardiography. LV diastolic dysfunction with normal ejection fraction (EF) was defined as follows: EF of > 50% and (a) E/e' ratio > 15, or (b) E/e' ratio of 8-15 and left atrial volume index ≥ 34 mL/m2. Subclinical hypothyroidism was significantly associated with cardiac indices regarding LV diastolic dysfunction. The odds of having LV diastolic dysfunction was also increased in participants with subclinical hypothyroidism (adjusted odds ratio [AOR] 1.36, 95% confidence interval [CI], 1.01-1.89) compared to euthyroid participants. Subclinical thyrotoxicosis was not associated with LV diastolic dysfunction. Among the thyroid hormones, only serum T3 was significantly and inversely associated with LV diastolic dysfunction even within the normal range. Subclinical hypothyroidism was significantly associated with LV diastolic dysfunction, whereas subclinical thyrotoxicosis was not. Serum T3 is a relatively important contributor to LV diastolic dysfunction compared to TSH or FT4.

The Impact of Physical Activity on Thyroid Health: Insights From Representative Data in Korea

CONTEXT

Thyroid hormones are essential for energy metabolism related to thermogenesis and oxygen consumption.

OBJECTIVE

This study evaluated the potential association of thyroid function including thyroid peroxidase antibodies (TPOAb) with physical activity in nationally representative data.

DESIGN/SETTING/PARTICIPANTS

This retrospective cohort study used data from the Korean National Health and Nutrition Examination Survey between 2013 and 2015. Physical activity (PA) was assessed using metabolic equivalents based on the validated Korean version of the International Physical Activity Questionnaire Short Form. PA level was categorized into 3 groups of high, moderate, and low. Participants with abnormal thyroid function test, restricted activity, or previous history of thyroid disease were excluded in the study.

RESULTS

A total of 5372 participants was finally selected. The free T4 level was lowest in the low PA group, while TSH was not significantly different among the groups. TPOAb titers increased in the following order: moderate PA, low PA, and high PA. After adjustment for confounding factors, moderate PA was associated with a high T4 level and a decrease in TSH and TPOAb with significance. However, there were no significant changes in free T4, TSH, or TPOAb titer in the high PA group. In a subanalysis, females with moderate PA showed a significant decrease in TSH and TPOAb. In both males and females, insulin sensitivity was increased with moderate PA. In obese participants, TSH negatively correlated with PA, and free T4 levels decreased in the low PA. The sensitivity to thyroid hormone did not differ in our study.

CONCLUSION

The present study found an association between thyroid function and moderate PA. Therefore, moderate-intensity PA should be recommended to improve thyroid function.

Protective effect of higher free thyroxine levels within the reference range on biliary tract cancer risk: a multivariable mendelian randomization and mediation analysis

Background

Hepatobiliary cancer (HBC), including hepatocellular carcinoma (HCC) and biliary tract cancer (BTC), is currently one of the malignant tumors that mainly cause human death. Many HBCs are diagnosed in the late stage, which increases the disease burden, indicating that effective prevention strategies and identification of risk factors are urgent. Many studies have reported the role of thyroid hormones on HBC. Our research aims to assess the causal effects and investigate the mediation effects between thyroid function and HBC.

Methods

Utilizing the Mendelian randomization (MR) approach, the study employs single nucleotide polymorphisms (SNPs) as instrumental variables (IVs) to explore causal links between thyroid function [free thyroxine (FT4), thyroid stimulating hormone (TSH), hyperthyroidism and hypothyroidism] and HBC. Data were sourced from the ThyroidOmic consortium and FinnGen consortium. The analysis included univariable and multivariable MR analysis, followed by mediation analysis.

Results

The study found a significant causal association between high FT4 levels and the reduced risk of BTC, but not HCC. However, TSH, hyperthyroidism and hypothyroidism had no causal associations with the risk of HBC. Notably, we also demonstrated that only higher FT4 levels with the reference range (FT4-RR) could reduce the risk of BTC because this protective effect no longer existed under the conditions of hyperthyroidism or hypothyroidism. Finally, we found that the protective effect of FT4-RR on BTC was mediated partially by decreasing the risk of metabolic syndrome (MetS) and reducing the waist circumference (WC).

Conclusion

The findings suggest that higher FT4-RR may have a protective effect against BTC, which is partially mediated by decreased risk of MetS and a reduction in WC. This study highlights the potential role of FT4 in the pathogenesis of BTC and underscores that MetS and WC may play mediation effects as two mediators in this process.

Thyroid Hormones and Diabetes in Euthyroid Hispanic/Latino Adults of Diverse Backgrounds: HCHS/SOL

Context

Previous studies have demonstrated associations of endogenous thyroid hormones with diabetes; less is known about stages of diabetes development at which they are operative, mechanisms of associations, and the role of the hypothalamic-pituitary-thyroid axis.

Objective

This study examined associations of thyroid hormones with incident prediabetes and diabetes and with changes in glycemic traits in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), the largest cohort of Hispanic/Latino adults with diverse backgrounds in the United States.

Methods

The study includes 592 postmenopausal euthyroid women and 868 euthyroid men aged 45 to 74 years without diabetes at baseline participating in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL). Baseline hormones included thyrotropin (TSH), free thyroxine (FT4), total triiodothyronine (T3), and indices calculated from thyroid hormones evaluating pituitary sensitivity to thyroid hormone. Transitions to diabetes and prediabetes, and changes in glycemic traits determined at the 6-year follow-up visit, were examined using multivariable Poisson and linear regressions.

Results

Among women, T3 (incident rate ratio [IRR] = 1.65; 95% CI, 1.22-2.24; P = .001) and TSH (IRR = 2.09; 95% CI, 1.01-4.33; P = .047) were positively, while FT4 (IRR = 0.59; 95% CI, 0.39-0.88; P = .011) was inversely, associated with transition from prediabetes to diabetes. Among men, the T3/FT4 ratio was positively associated with transition from normoglycemia to prediabetes but not from prediabetes to diabetes. Indices measuring sensitivity of the pituitary to thyroid hormone suggested increased sensitivity in men who transitioned from prediabetes to diabetes.

Conclusion

Positive associations in women of T3 and TSH and inverse associations of FT4, as well as inverse associations of thyroid indices in men with transition from prediabetes to diabetes, but not from normoglycemia to diabetes, suggest decreased pituitary sensitivity to thyroid hormones in women and increased sensitivity in men later in the development of diabetes.

Association of thyroid function with non-alcoholic fatty liver disease in recent-onset diabetes

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) has been linked to type 2 diabetes (T2D), but also to hypothyroidism. Nevertheless, the relationship between thyroid function and NAFLD in diabetes is less clear. This study investigated associations between free thyroxine (fT4) or thyroid-stimulating hormone (TSH) and NAFLD in recent-onset diabetes.

METHODS

Participants with recent-onset type 1 diabetes (T1D, n = 358), T2D (n = 596) or without diabetes (CON, n = 175) of the German Diabetes Study (GDS), a prospective longitudinal cohort study, underwent Botnia clamp tests and assessment of fT4, TSH, fatty liver index (FLI) and in a representative subcohort 1 H-magnetic resonance spectroscopy.

RESULTS

First, fT4 levels were similar between T1D and T2D (p = .55), but higher than in CON (T1D: p < .01; T2D: p < .001), while TSH concentrations were not different between all groups. Next, fT4 correlated negatively with FLI and positively with insulin sensitivity only in T2D (ß = -.110, p < .01; ß = .126, p < .05), specifically in males (ß = -.117, p < .05; ß = .162; p < .01) upon adjustments for age, sex and BMI. However, correlations between fT4 and FLI lost statistical significance after adjustment for insulin sensitivity (T2D: ß = -.021, p = 0.67; males with T2D: ß = -.033; p = .56). TSH was associated positively with FLI only in male T2D before (ß = .116, p < .05), but not after adjustments for age and BMI (ß = .052; p = .30).

CONCLUSIONS

Steatosis risk correlates with lower thyroid function in T2D, which is mediated by insulin resistance and body mass, specifically in men, whereas no such relationship is present in T1D.

The effect of hypothyroidism on the risk of diabetes and its microvascular complications: a Mendelian randomization study

Context

Several observational studies have found that hypothyroidism is associated with diabetes and its microvascular complications. However, the cause and effect have not been clarified.

Objective

The aim of the study was to examine the causality of such associations by a Mendelian randomization study.

Methods

Two-sample Mendelian randomization analysis was conducted to investigate the associations. Summary statistics for hypothyroidism were from the UK Biobank, and diabetes and its microvascular complications were from the largest available genome-wide association studies. MR-Egger, weighted median, inverse variance weighted, simple mode and weighted mode were used to examine the causal associations, and several sensitivity analyses were used to assess pleiotropy.

Results

Inverse variance weighted estimates suggested that hypothyroidism was associated with type 1 diabetes and type 1 diabetes with renal complications (β= 9.059926, se= 1.762903, P = 2.76E-07 and β= 10.18375, se= 2.021879, P = 4.73E-07, respectively) but not type 2 diabetes and type 2 diabetes with renal complications. In addition, hypothyroidism was positively associated with severe nonproliferative diabetic retinopathy and proliferative diabetic retinopathy (β= 8.427943, se= 2.142493, P = 8.36E-05 and β= 3.100939, se= 0.74956, P=3.52E-05, respectively).

Conclusions

The study identified the causal roles of hypothyroidism in diabetes and its microvascular complications. Hypothyroidism can lead to type 1 diabetes, type 1 diabetes with renal complications, severe nonproliferative diabetic retinopathy and proliferative diabetic retinopathy.

Humero-femoral index and diabetes risk in the US population- a case study

Background

The between-subject variability in diabetes risk persists in epidemiological studies, even after accounting for obesity. We investigated whether the humero-femoral index (HFI) was associated with prevalence of type 2 diabetes mellitus (T2DM) and assessed the incremental value of HFI as a marker of T2DM.

Methods

This population-based cross-sectional study used data from the National Health and Nutrition Examination Survey from 1999 to 2018. We assessed 42,088 adults aged ≥ 30 years. HFI was defined as the upper arm length/upper leg length ratio. The outcome included undiagnosed diabetes (based on 2-hour plasma glucose levels, fasting glucose and hemoglobin A1C) and history of diabetes (diagnosed diabetes or taking antidiabetic drugs).

Results

As compared with the bottom quartile, the prevalence ratio of T2DM was 1.28 (95% CI 1.19-1.38) in the second, 1.61 (95% CI 1.50-1.72) in the third, and 1.75 (95% CI 1.64-1.88) in the fourth quartile of HFI (P for trend < 0.0001). The positive association remained consistent within different patterns of BMI and WC in men but was rendered null in women. After adding HFI to the reference model (including WC only), the discrimination slopes increased by 60.0% in men and 51.1% in women.

Conclusion

Our findings suggest that HFI may be a key component in body structure contributing to the risk of T2DM. In men, the highest HFI was associated with elevated prevalence of T2DM, independent of BMI and WC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01251-z.

Maternal pre-pregnancy obesity modifies the association between first-trimester thyroid hormone sensitivity and gestational Diabetes Mellitus: a retrospective study from Northern China

BACKGROUND

Contradictory relationships have been observed between thyroid function and gestational diabetes mellitus (GDM). Previous studies have indicated that pre-pregnancy BMI (pBMI) could modify their relationships. Few studies have illustrated the role of thyroid hormone sensitivity on GDM. We aimed to explore the effect of pre-pregnancy obesity on the association between early pregnancy thyroid hormone sensitivity and GDM in euthyroid pregnant women.

METHODS

This study included 1310 women with singleton gestation. Subjects were classified into pre-pregnancy obese and non-obese subgroups by pBMI levels with a cutoff of 25 kg/m2. Sensitivity to thyroid hormone was evaluated by Thyroid Feedback Quartile-Based Index (TFQI), Chinese-referenced parametric TFQI (PTFQI), TSH Index (TSHI) and Thyrotrophic T4 Resistance Index (TT4RI). The associations between these composite indices and GDM were analyzed using multivariate regression models in the two subgroups, respectively.

RESULTS

In pre-pregnancy non-obese group, early pregnancy TFQI, PTFQI, TSHI and TT4RI levels were higher in subjects with incident GDM compared to those without GDM (all P < 0.05). By contrast, obese women with GDM exhibited lower levels of those indices (all P < 0.05). The occurrence of GDM were increased with rising TFQI, PTFQI, TSHI and TT4RI quartiles in non-obese women ( all P for trend < 0.05), while exhibited decreased trend across quartiles of those indices in obese women (all P for trend < 0.05). Further logistic analysis indicated contrary relationships between thyroid hormone sensitivity and the occurrence of GDM in the two groups, respectively. The OR of the fourth versus the first quartile of TFQI for GDM was 1.981 (95% CI 1.224, 3.207) in pre-pregnancy non-obese group, while was 0.131 (95% CI 0.036, 0.472) in pre-pregnancy obese group. PTFQI and TSHI yielded similar results.

CONCLUSIONS

The association between maternal sensitivity to thyroid hormones during early gestation and the occurrence of GDM was modified by pre-pregnancy obesity.

HbA1c: an independent risk factor for dysthyroid optic neuropathy

Background

We aimed to explore the frequencies of islet β-cell autoantibodies and insulin resistance (IR) in thyroid-associated ophthalmopathy (TAO) and identify specific diabetes mellitus (DM) indicators as early predictors for dysthyroid optic neuropathy (DON).

Methods

Ninety-eight TAO patients (57 DON and 41 non-DON patients) and 48 healthy control (HC) participants were recruited for this prospective cross-sectional study. Serum thyroxine, serum thyroid autoantibodies, serum humoral immune markers against islet β-cell, fasting plasma glucose (FPG), fasting serum insulin (FINS), fasting c-peptide (FCP), and glycosylated hemoglobin A1 (HbA1c) were measured. Logistic regression analysis was used to evaluate the correlation of patients' age, body mass index (BMI), FPG, HbA1c, and related indexes of islet β-cell function to the occurrence of DON.

Results

The DON group had higher FPG (P<0.001, 0.016) and HbA1c (P<0.0001, P<0.001) levels than the HC and non-DON groups. The homeostasis model assessment (HOMA)-IR level was the highest in the DON group (HC 2.15 ± 0.89, non-DON 2.41 ± 1.24, and DON 2.82 ± 2.65), while the HOMA-β level was the lowest (HC 101.8 ± 44.75%, non-DON 102.9 ± 54.61%, and DON 88.29 ± 52.75%), with no significant differences (P=1, P>0.05). On univariate analysis, age (P=0.006), BMI (P=0.022), history of steroid use (P=0.014), FPG (P=0.013), and HbA1c (P=0.001) levels were significantly associated with the presence/absence of DON. In addition, after adjusting for potential confounds, the HbA1c level was an independent factor associated with DON (P=0.009, OR=4.012).

Conclusions

HbA1c is an independent risk factor for DON. Given the interconnected link between thyroid dysfunction and DM, the use of HbA1c as a potential biomarker for DON warrants further investigation.

The effect of Central and peripheral thyroid resistance indices on diabetic retinopathy: a study of hospitalized euthyroid patients with T2DM in China

OBJECTIVE

This study aims to explore the correlation between central and peripheral thyroid resistance indices and diabetic retinopathy(DR) in patients with type 2 diabetes mellitus (T2DM), so as to provide a clinical basis for the prevention and treatment of diabetic retinopathy.

METHODS

This study retrospectively analyzed 1249 euthyroid patients with T2DM hospitalized in the Department of Endocrinology, Peking University International Hospital from January 2017 to June 2022, including 852 males and 397 females, with an average age of 54.73 ± 13.40 years. According to the degree of DR, the patients were divided into three groups including the no diabetic retinopathy (NDR) group, non-proliferative diabetic retinopathy (NPDR) group and proliferative diabetic retinopathy (PDR) group.

RESULTS

Free thymidine (FT4), thyroid stimulating hormone (TSH), thyroid feedback quantile index (TFQI), thyrotropin-T4 resistance index (TT4RI), thyroid stimulating hormone index (TSHI) and free triiodothyronine/free thyroxine (FT3/FT4) levels among the three groups were significantly different, with the NDR group having lowest TSH, TFQI, TT4QI, TSHI and the highest in the PDR group (all p < 0.05). Logistic regression showed that after adjusting for age, body mass index (BMI), sex, diabetes duration, blood pressure, blood lipid, HbA1c, lower level of FT4 was an independent risk factor for DR, high level of TSH, TFQI, TSHI and TT4RI were independent risk factors for DR. Central and peripheral thyroid sensitivity indices have predictive value for DR, the overall predictive accuracy of FT3/FT4 was 0.61 (95%CI 0.57, 0.65), the overall predictive accuracy of TFQI was 0.66(95%CI 0.63, 0.70), the overall predictive accuracy of TSHI was 0.66(95%CI 0.62, 0.68), the overall predictive accuracy of TT4RI was 0.63 (95%CI 0.59, 0.66).

CONCLUSION

The reduction of central and peripheral thyroid hormone sensitivity is an independent risk factor for DR. These results can help predict the risk of the occurrence and development of DR, which may provide a clinical basis for the prevention and treatment of DR in T2DM patients.

Subclinical hypothyroidism increases insulin resistance in normoglycemic people

Objective

To investigate the effect of simple subclinical hypothyroidism (SCH) and type 2 diabetes mellitus (T2DM) combined with SCH on insulin resistance.

Design and methods

A total of 622 people with newly diagnosed T2DM were selected as the study subjects, and 621 normoglycemic people were selected as control subjects. According to the diagnostic criteria of thyroid diseases, the subjects were divided into a normal thyroid function group and a subclinical hypothyroidism group. Both groups received a physical examination, and blood samples were collected. The measurement indexes included FPG, FINS, OGTT2hPG, OGTT2hINS, HbA1c, TC, TG, HDL-C, LDL-C, TSH, FT3 and FT4. HOMA-IR, HOMA-β, and TFQI (thyroid feedback quantile index) were calculated.

Results

There was no significant difference in age or sex distribution between the T2DM group and the normoglycemic group (P>0.05). The prevalence of thyroid dysfunction in the T2DM group was significantly higher than that in the normoglycemic group (16.39% vs. 11.27%, P<0.05), and among the different types of thyroid dysfunction, the prevalence of SCH was the highest at 14.95% (P<0.05). There was no significant difference in BMI, waist-hip ratio, blood lipid profile, HOMA-β, and HOMA-IR values between the T2DM with subclinical hypothyroidism group (T2DM+SCH+ group) and the normal thyroid function group (T2DM+SCH- group) (P>0.05). The BMI, waist-hip ratio and HOMA-IR values of the normoglycemic group with subclinical hypothyroidism (T2DM-SCH+ group) were significantly higher than those of the normoglycemic group with normal thyroid function (T2DM-SCH- group) (P<0.05), and there were no significant differences between the T2DM+SCH- and T2DM+SCH+ groups (P>0.05). HOMA-β values were significantly higher in the T2DM-SCH+ group than in the T2DM-SCH-, T2DM+SCH- and T2DM+SCH+ groups (P<0.05). As the TFQI value increased, the body weight, waist-hip ratio, diastolic blood pressure, FPG, OGTT2hPG and HbA1c values gradually increased in the T2DM group and normoglycemic group (P<0.05). HDL-C, FINS, OGTT2hINS and HOMA-β values gradually decreased (P<0.05).

Conclusion

Subclinical hypothyroidism only increases insulin resistance in normoglycemic people. As the sensitivity of the central thyroid decreases, the risk of developing diabetes increases.

The Correlation Between Health Risk Factors and Diabesity and Lipid Profile Indicators: The Role Mediator of TSH

Introduction

Obesity in adults is a problem, particularly when paired with other metabolic abnormalities. Previous research have linked various screening approaches to diabetes, but additional evidence points to the relevance of combining diabetes screening methods with obesity and its effects. This research examined the impact of thyroid hormones (TSHs) and health risk factors (HRFs) in screening for obesity and diabetes in Chinese populations, and whether age can modulate this association.

Methods

From March to July 2022, the Hefei Community Health Service Center connected with the First Affiliated Hospital of Anhui Medical University was chosen, and the multi-stage cluster sample approach was utilized to test adults aged 21-90 in each community. Latent category analysis (LCA) was performed to investigate the clustering patterns of HRFs. A one-way ANOVA was used to examine waist circumference (WC), biochemical markers, and general data. Furthermore, multivariate logistic regression analysis was utilized to investigate the relationship between health risk variables and WC.

Results

A total of 750 individuals without a history of major problems who had a community health physical examination were chosen, with missing data greater than 5% excluded. Finally, 708 samples were included in the study with an effective rate of 94.4%. The average WC was (90.0±10.33) cm, the prevalence in the >P₇₅, P₅₀~P₇₅, P₂₅~P₅₀, and ≤P₂₅ groups were 24.7%, 18.9%, 28.7% and 27.7%, respectively. The average TSH was (2.76±2.0) μIU/mL. Male (β=1.91), HOMA-IR (β=0.06), TyG (β=2.41), SBP (β=0.08), TG (β=0.94) and UA (β=0.03) were more likely to have a higher prevalence of WC level. The analyses revealed significant correlations between HRFs, TSH, age, other metabolic indexes and WC (P < 0.05).

Discussion

Our findings suggest that the quality of metabolic-related indicators used to successfully decrease diabetes in Chinese individuals with high HRFs levels should be prioritized. Comprehensive indicators might be a useful and practical way for measuring the metabolic evolution of diabetes level levels.

Redefinition of Successful Treatment of Patients With Hypothyroidism. Is TSH the Best Biomarker of Euthyroidism?

In recent years evidence has accumulated supporting a revised view of the nature of euthyroidism and the biomarkers of thyroid function. Within the normal range, variations in thyroid hormone levels are associated with variations in clinical parameters and outcomes. There are therefore no readily identified individually specific optimum levels of thyroid hormones for any individual. Levels around the middle of the normal population range may best reflect euthyroidism. These levels may have evolutionary advantages on the basis that adverse outcomes often increase with divergence from such levels, and physiological processes tend to minimise such inter-individual and intra-individual divergence. In populations of predominantly untreated individuals, levels of thyroid hormones and in particular levels of free thyroxine (FT4) correlate more often with clinical parameters than do levels of thyrotropin (TSH). Levels of thyroid hormones may therefore be regarded as the best available biomarkers of euthyroidism and dysthyroidism. It follows that 'subclinical hypothyroidism' (normal FT4/raised TSH levels), rather than being an accurate marker of peripheral tissue hypothyroidism is more a marker of decreased thyroid reserve and prognosis. The recent evidence suggests that treatment of hypothyroxinemia, regardless of the TSH level, and monitoring therapy using FT4 and/or triiodothyronine levels, depending on the replacement regime, may result in more successful treatment of hypothyroidism than relying on thyrotropin levels for patient selection and subsequent treatment monitoring. The equivalents of mid-range levels of thyroid hormones (especially FT4), adjusted by individual comorbidity concerns, may be rational general replacement targets. These implications of the new evidence may create opportunities for novel trials of thyroid replacement therapy.

Thyroid-Stimulating Hormone and Thyroid Hormones and Incidence of Diabetes: Prospective Results of the Brazilian Longitudinal Study of Adult Health (ELSA-BRASIL)

Background: There are conflicting data regarding the association of thyroid function with incident diabetes. We prospectively investigated thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), and its conversion ratio (fT3:fT4) with the risk of developing diabetes in euthyroid subjects and those with subclinical thyroid dysfunction. Our hypothesis is that this relationship is a U-shaped curve since both subclinical thyroid diseases may be associated with diabetes. Methods: ELSA-Brasil is a highly admixed cohort study of 35-74 years old at baseline (2008-2010). Levels of TSH, fT4, fT3, and fT3:fT4 ratio were evaluated at baseline and incident diabetes was estimated over an 8.2-year follow-up (2017-2019). Diabetes was identified based on medical diagnosis, prescriptions, and laboratory tests. The risk of diabetes was evaluated according to quintiles of TSH, fT4, fT3, and fT3:fT4 ratio using Poisson regression with robust variance presented as relative risk (RR) with confidence interval [CI] of 95% after multivariable adjustment for sociodemographic and cardiovascular risk factors (reference third quintile), and as continuous variables. Results: We included 7948 participants (mean age, 50.2 [standard deviation 8.6] years; 54.4% female): 7177 euthyroid, 726 with subclinical hypothyroidism, and 45 with subclinical hyperthyroidism. Incidence of diabetes was 14.8%. No association was found for TSH, fT4, fT3, and fT3:fT4 ratio quintiles with incident diabetes. Using continuous variables, the increase of 1-unit (1-U) of fT4 decreased the risk of diabetes (RR 0.94 [CI 0.91-0.99]), while the increase of 1-U of the fT3:fT4 ratio increased the diabetes risk (RR 1.37 [CI 1.15-1.63]). The increase of 1-U of fT3 was associated with an increased risk of diabetes, but without significance after multivariable adjustment. In body mass index-stratified analysis, people with overweight or obesity presented a modest significantly higher risk of diabetes in the lowest quintile of fT4 (RR 1.04 [CI 1.01-1.07]) and an inverse association with incident diabetes in the first quintile of fT3:fT4 ratio (RR, 0.95 [CI 0.93-0.98]). The analyses using continuous variables presented similar findings. Conclusion: These findings suggest that fT4 and fT3 levels and the conversion rate might be additional risk factors associated with incident diabetes, especially in the presence of overweight or obesity. However, they need to be confirmed in future studies. (ClinicalTrials.gov Identifier: NCT02320461).

Impaired Sensitivity to Thyroid Hormones Is Associated with Hyperuricemia, Obesity, and Cardiovascular Disease Risk in Subjects with Subclinical Hypothyroidism

Background: Subclinical hypothyroidism (SCH) is associated with an increased risk of metabolic disorders and cardiovascular events. There is a delicate interplay between thyroid hormones and thyrotropin (TSH) and metabolic homeostasis. However, the association between thyroid hormone sensitivity and metabolic indices has not been elucidated in SCH. Methods: We enrolled 11,109 participants with SCH. All participants had a TSH level >4.2 mIU/L and normal free thyroxine (fT4; 12.0-22.0 pmol/L). Metabolic indices (body mass index [BMI], blood pressure, serum lipid, serum uric acid [sUA], plasma glucose and glycosylated hemoglobin [HbA1_C]) were measured. The thyroid hormone sensitivity indices that include thyroid feedback quantile-based index (TFQI), TSH index (TSHI), and thyrotroph thyroxine resistance index (TT4RI) were calculated based on fT4 and TSH. Higher TFQI quartiles indicated lower thyroid hormone sensitivity. The relationship between thyroid hormone sensitivity indices and metabolic indices and cardiovascular disease (CVD) risk were calculated. Results: Participants with decreased central sensitivity to thyroid hormone had lower BMI and higher sUA levels. The odds ratio of the fourth versus the first quartile of TFQI was 0.85 [confidence interval, CI: 0.73-0.96] for obesity, 1.64 [CI: 1.37-1.92] for hyperuricemia (HUA), and 12.22 [CI: 5.32-28.07] for 10-year risk distribution for CVD >20%. Further adjustment for BMI when analyzing HbA1_C, HUA, and CVD risk generated similar results. TSHI and TT4RI also yielded similar results. Conclusions: Impaired sensitivity to thyroid hormone in SCH is associated with higher risk of HUA and CVD and lower risk of obesity. These findings are potentially useful for understanding the interaction between thyroid hormone sensitivity and metabolic diseases in SCH.

Hypothyroidism and Diabetes-Related Dementia: Focused on Neuronal Dysfunction, Insulin Resistance, and Dyslipidemia

The incidence of dementia is steadily increasing worldwide. The risk factors for dementia are diverse, and include genetic background, environmental factors, sex differences, and vascular abnormalities. Among the subtypes of dementia, diabetes-related dementia is emerging as a complex type of dementia related to metabolic imbalance, due to the increase in the number of patients with metabolic syndrome and dementia worldwide. Thyroid hormones are considered metabolic regulatory hormones and affect various diseases, such as liver failure, obesity, and dementia. Thyroid dysregulation affects various cellular mechanisms and is linked to multiple disease pathologies. In particular, hypothyroidism is considered a critical cause for various neurological problems-such as metabolic disease, depressive symptoms, and dementia-in the central nervous system. Recent studies have demonstrated the relationship between hypothyroidism and brain insulin resistance and dyslipidemia, leading to diabetes-related dementia. Therefore, we reviewed the relationship between hypothyroidism and diabetes-related dementia, with a focus on major features of diabetes-related dementia such as insulin resistance, neuronal dysfunction, and dyslipidemia.

Longitudinal changes in blood biomarkers and their ability to predict type 2 diabetes mellitus—The Tromsø study

Introduction

Methods

Results

Conclusion

Antidiabetic Medications and the Risk of Prostate Cancer in Patients with Diabetes Mellitus: A Systematic Review and Meta-analysis

BACKGROUND

Antidiabetic medications (ADMs) may modify prostate cancer (PCa) risk in patients with diabetes mellitus (DM). Accordingly, the current study assessed the possible associations between ADMs and the risk of PCa in diabetics.

METHODS

A systematic literature search (PubMed, Embase and Cochrane Library) identified studies evaluating the associations between ADMs and incidence of PCa. A meta-analysis followed PRISMA was performed using odds ratio (OR) with 95% confidence interval (CI) as effect measures.

RESULTS

In total of 47 studies involving 3,094,152 patients with diabetes were included. Results of meta-analysis of the observational studies suggested no significant association between metformin, thiazolidinediones, sulfonylureas, insulin or dipeptidyl peptidase-4 inhibitors administration and the risk of PCa (All p-values > 0.05). Separate analysis of randomized controlled trials (RCTs) revealed a significant reduction in PCa risk with thiazolidinediones (OR = 0.55, p = 0.04) or glucagon-like peptide-1 receptor agonists (GLP-1RA) administration (OR = 0.53, p = 0.006), whereas no significant association was found in SGLT2 inhibitors (p = 0.3).

CONCLUSION

Thiazolidinediones or GLP-1RA administration may have benefits in PCa based on RCTs, however, further research is needed to confirm these findings.

Impaired Sensitivity to Thyroid Hormones Is Associated With Elevated Blood Glucose in Coronary Heart Disease

CONTEXT

Thyroid hormones influence glucose homeostasis through central and peripheral regulation. To date, the association between thyroid hormone sensitivity and elevated blood glucose (EBG) in patients with coronary heart disease (CHD) remains unknown. The purpose of this study was to investigate the association between thyroid hormone sensitivity and risk of EBG in patients with CHD, and to further explore their association in different sexes and ages.

METHODS

This large multicenter retrospective study included 30,244 patients with CHD (aged 30-80 years) between 1 January 2014 and 30 September 2020. Parameters representing central and peripheral sensitivity to thyroid hormones were calculated. Central sensitivity to thyroid hormones was assessed by calculating the Thyroid Feedback Quantile-based Index (TFQI), Thyroid-stimulating Hormone Index (TSHI), and Thyrotropin Thyroxine Resistance Index (TT4RI), and Parametric Thyroid Feedback Quantile-based Index (PTFQI); peripheral sensitivity to thyroid hormones was evaluated using the ratio of free triiodothyronine (FT3) /free thyroxine (FT4). Taking normal glucose tolerance (NGT) as a reference, logistic regression was used to analyse the relationship between central and peripheral thyroid hormone sensitivity and EBG in patients with CHD.

RESULTS

Among the 30,244 participants, 15,493 (51.23%) had EBG. The risk of EBG was negatively correlated with TSHI (OR: 0.91; 95%CI: 0.91 to 0.92; P < 0.001), TT4RI (OR: 0.99; 95% CI: 0.99 to 0.99; P<0.001), TFQI (OR: 0.82; 95%CI: 0.80 to 0.84; P <0.001) and PTFQI (OR: 0.76; 95%CI: 0.74 to 0.78; P<0.001). Compared to males and patients aged 60 and below, the OR value for EBG was lower in females and in patients aged over 60 years old. Conversely, EBG risk was positively associated with FT3/FT4 (OR: 1.08; 95% CI: 1.07 to 1.09; P <0.001) and in the sex-categorized subgroups, males had higher OR values than females.

CONCLUSIONS

This study showed that thyroid hormone sensitivity is significantly associated with EBG in patients with CHD. This association is higher in females than in males, and the association in those aged over 60 years old is higher than that in patients aged 60 years and below.

Reduced Sensitivity to Thyroid Hormone Is Associated with Diabetes and Hypertension

CONTEXT

Recently, reduced sensitivity to thyroid hormone as a more common finding in the general population and its possible association with metabolic parameters has been the focus of attention.

OBJECTIVE

The objective was to evaluate the cross-sectional association of thyroid hormone sensitivity with diabetes, metabolic syndrome (MetS), and its components.

METHODS

The study included a Tehranian representative sample of 5124 subjects aged ≥20 years participating in the Tehran Thyroid Study (2008-2011). Body weight, waist circumference, and blood pressure (BP) were measured, and serum concentrations of lipids and lipoproteins, fasting blood glucose, insulin, free thyroxine (fT4), and thyrotropin (TSH) were assayed. Thyroid hormone resistance was calculated by the Thyroid Feedback Quantile-based Index (TFQI) and Iranian-referenced Parametric TFQI (PTFQI) and compared with 2 other indices: Thyrotroph T4 Resistance Index (TT4RI) and TSH Index.

RESULTS

TFQI was significantly associated with high BP MetS criterion (OR = 1.14, 95% CI: 1.06, 1.23) and diabetes mellitus (OR = 1.16, 95% CI: 1.04, 1. 30, P = .009) in euthyroid subjects after adjusting for age, sex, smoking, physical activity, body mass index, and Homeostasis Model Assessment Index for Insulin Resistance. TFQI was not associated with new-onset diabetes contrary to known diabetes in subgroup analysis. The results were similar for PTFQI. TSHI (OR = 1.22, 95% CI: 1.08, 1.38, P = .001) and TT4RI (OR = 1.08, 95% CI: 1.01, 1.16, P < .001) were associated only with high BP in euthyroid subjects.

CONCLUSION

The new TFQI index seems to be the indicator of reduced sensitivity to thyroid hormone most suitable to associate its population variations with diabetes and hypertension in euthyroid subjects; however, interpretation for diabetes should be concerned with cautions, necessitating future studies.

TSH Combined with TSHR Aggravates Diabetic Peripheral Neuropathy by Promoting Oxidative Stress and Apoptosis in Schwann Cells

Subclinical hypothyroidism (SCH) is associated with diabetic peripheral neuropathy (DPN); however, the mechanism underlying this association remains unknown. This study is aimed at examining neurofunctional and histopathological alterations in a type 2 diabetes (T2DM) mouse model of SCH and investigating the impact of thyroid-stimulating hormone (TSH) in an in vitro DPN cell model established using RSC96 cells under high glucose (HG) and palmitic acid (PA) stimulation. Our results indicated that T2DM, in combination with SCH, aggravated abnormal glucose and lipid metabolism in T2DM and dramatically destroyed the peripheral nervous system by increasing paw withdrawal latency, decreasing motor nerve conduction velocity, and exacerbating ultrastructural deterioration of the damaged sciatic nerve caused by diabetes. Furthermore, the results of our in vitro experiments showed that TSH intensified HG/PA-induced RSC96 cell damage by inducing oxidative stress, mitochondrial dysfunction, and apoptosis. More importantly, TSHR knockout or inhibition of PA-induced TSHR palmitoylation could alleviate the apoptosis induced by TSH. Overall, in this study, the novel mechanisms by which TSH, as an independent risk factor for DPN progression, aggravating Schwann cell apoptosis and demyelination, are elucidated. These findings indicate that TSHR could be a potential target for both the prevention and treatment of DPN and, possibly, other microvascular diseases, and have implication in the clinical management of patients with DPN.

Association between thyroid dysfunction and type 2 diabetes: a meta-analysis of prospective observational studies

BACKGROUND

Diabetes mellitus and thyroid disease are two areas of broad interest in the field of endocrinology and metabolism. Variation of thyroid hormone concentration, even within the normal range, may portend the onset of type 2 diabetes mellitus (T2DM), especially among those with prediabetes. However, current evidence is mixed.

METHODS

Prospective studies which assessed diabetes incidence were identified using a database search of MEDLINE and Embase through May 1, 2021. The Sidik-Jonkman random-effects model and cubic spline model were used to evaluate the associations and dose-response relationships between thyroid function/hormone levels and risk of T2DM and cardiovascular disease (CVD) risk among T2DM patients.

RESULTS

A total of 12 prospective studies were included. We found that high baseline TSH levels were related to a 17% higher risk of T2DM (RR 1.17, 95% CI 1.01, 1.36; I²=78%, P<0.01), compared with normal TSH levels. Low FT3 (RR 1.40, 95% CI 1.09, 1.80; I²=59%, P=0.03) and low FT4 (RR 1.33, 95% CI 1.04, 1.71; I²=62%, P=0.02) levels were significantly associated with risk of T2DM. The cubic spline model indicated a J-shaped relationship with TSH, but inverted-J-shaped relationships with FT3 and FT4. CVD events and all-cause deaths were prospectively evaluated in four studies, but were not associated with abnormal thyroid function.

CONCLUSIONS

Our meta-analysis determined that abnormal thyroid hormone level is associated with an increased risk of T2DM, showing a J-shaped relationship with TSH and inverted-J-shaped relationships with FT3 and FT4.

TRIAL REGISTRATION

Registered number in PROSPERO: CRD42021225695 .

Metabolic syndrome and its components are associated with thyroid volume in adolescents

OBJECTIVE

To explore the association between metabolic syndrome (MetS) and its component and thyroid volume in Chinese adolescents, and to compare the detection rate of MetS under the three different diagnostic criteria.

METHODS

A total of 1097 school students (610 males and 487 females, ages 12-15 years) were enrolled. All the participants underwent physical examination, biochemical test, and thyroid gland ultrasonography. The thyroid volume of normal, overweight and obese group was compared. We also analyzed the association between the number of MetS components and thyroid volume. Linear and multiple linear regression were applied to explore the association between metabolic parameters and thyroid volume.

RESULTS

The thyroid volume of the males in overweight (t = 3.784, P < 0.001) and obese group (t = 5.068, P < 0.001) was significantly larger than that in normal group; the thyroid volume of the females in overweight group (t = 4.627,P < 0.001) was significantly larger than that of normal group. As the number of MetS components increased, the thyroid volume also increased significantly (F = 10.64, P < 0.01). Height, weight, body mass index (BMI), waist circumference, hip circumference, systolic blood pressure, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), uric acid and triglyceride were all positively associated with thyroid volume in the adolescents (P all < 0.001). Meanwhile, there was a negative association between high-density lipoprotein cholesterol (HDL-C) and thyroid volume (P < 0.001). According to multiple linear regression, waist circumference (β = 0.029, 95 %CI: 0.015 ~ 0.042; P < 0.01) and waist height ratio (β = 3.317, 95 %CI: 1.661 ~ 4.973; P < 0.01) were predict factors of thyroid volume. No statistical difference was found in the detection rates of metabolic syndrome under the three diagnostic criteria.

CONCLUSIONS

Overweight, obesity and metabolic syndrome was associated with adolescent thyroid volume. Central obesity may be an independent risk factor for thyroid enlargement in adolescents.

Relationship of TSH Levels with Cardiometabolic Risk Factors in US Youth and Reference Percentiles for Thyroid Function

CONTEXT

Thyroid hormones play an important role in metabolic homeostasis, and higher levels have been associated with cardiometabolic risk.

OBJECTIVE

To examine the association of cardiometabolic risk factors with TSH levels in US youth.

METHODS

Cross-sectional study of youth aged 12 to 18 years without known thyroid abnormalities from 5 National Health and Nutrition Examination Survey cycles (n = 2818) representing 15.4 million US children. Subclinical hypothyroidism (SH) was defined as thyrotropin (TSH) levels of 4.5 to 10 mIU/L. Assessed cardiometabolic risk factors include abdominal obesity (waist circumference >90th percentile), hypertriglyceridemia (triglyceride ≥130 mg/dL), low high-density lipoprotein cholesterol (<40 mg/dL), elevated blood pressure (systolic and diastolic blood pressure ≥90th percentile), hyperglycemia (fasting blood glucose ≥100 mg/dL, or known diabetes), insulin resistance (homeostatic model for insulin resistance > 3.16), and elevated alanine transferase (≥ 50 for boys and ≥44 U/L for girls). Age and sex- specific percentiles for thyroid parameters were calculated.

RESULTS

In this cohort of youth (51.3% male), 31.2% had overweight/obesity. The prevalence of SH was 2.0% (95% CI 1.2-3.1). The median TSH levels were higher in youth with overweight/obesity (P < 0.001). Adjusting for age, sex, race/ethnicity, and obesity, youth with TSH in the fourth quantile had higher odds of abdominal obesity (OR 2.53 [1.43-4.46], P = .002), insulin resistance (OR 2.82 [1.42-5.57], P = .003), and ≥2 cardiometabolic risk factors (CMRF) (OR 2.20 [1.23-3.95], P = .009).

CONCLUSION

The prevalence of SH is low in US youth. The higher odds of insulin resistance and cardiometabolic risk factors in youth with TSH levels >75th percentile requires further study.

Association Between Serum Thyroid-Stimulating Hormone Levels and Salivary Microbiome Shifts

High serum thyroid-stimulating hormone (TSH) levels are linked to many metabolic disorders, but the effects of TSH levels on the oral microbiota are still largely unknown. This study aimed to explore the association between the salivary microbiome in adults and serum TSH levels. Saliva and fasting blood samples were obtained from a health census conducted in Southeast China. All participants were divided according to serum TSH levels. The microbial genetic profiles and changes were acquired by 16S rDNA sequencing and bioinformatics analysis. Relevant anthropometric and biochemical measurements such as insulin resistance, blood lipids, and body composition were evaluated with laboratory tests and physical examinations. The salivary microbiome in individuals with higher TSH level showed significantly higher taxa diversity. Principal coordinates analysis and partial least squares discriminant analysis showed distinct clustering in the Abnormal and Normal Groups (Adonis, P=0.0320). Granulicatella was identified as a discriminative genus for comparison of the two groups. Fasting serum insulin, Homeostatic Model Assessment for Insulin Resistance, and hemoglobin A1 were elevated in the Abnormal Group (P<0.05), showing the presence of insulin resistance in individuals with abnormal higher serum TSH levels. Distance-based redundancy analysis revealed the association of this distinctive difference with salivary microbiome. In conclusion, shifts in microbial profile were observed in the saliva of individuals with different serum TSH levels, and insulin resistance may play an important role in the biochemical and microbial alteration.

Sensitivity to Thyroid Hormones and Risk of Prediabetes: A Cross-Sectional Study

CONTEXT

Thyroid hormone influences glucose homeostasis through central and peripheral regulations. To date, the link between sensitivity to thyroid hormones and prediabetes remains unknown. We aimed to investigate the association between thyroid hormones sensitivity and risk of prediabetes in both general and euthyroid populations.

METHODS

Participants with serum free triiodothyronine (FT3), free thyroxine (FT4), and thyrotropin (TSH) measurements from the health checkup programs of the First Hospital of China Medical University were collected. We measured the parameters representing central and peripheral sensitivities to thyroid hormones (central sensitivity, assessed by calculating Thyroid Feedback Quantile-based Index (TFQI), TSH Index (TSHI), and Thyrotroph Thyroxine Resistance Index (TT4RI); peripheral sensitivity, evaluated by FT3/FT4 ratio). Associations between thyroid hormones sensitivities and risk of prediabetes were assessed with logistic regression.

RESULTS

A total of 4378 participants (mean age ± SD, 49 ± 11 years) were included, with 1457 (33%) subjects had prediabetes. The risk of prediabetes was negatively associated with levels of TSHI (odds ratio [OR] 0.91; 95% confidence interval [CI], 0.85-0.97), TT4RI (OR 0.91; 95% CI, 0.84-0.99) and Parametric TFQI (PTFQI) (OR 0.89; 95% CI, 0.83-0.95) among all subjects. The association remained significant in euthyroid subjects and euthyroid subjects with negative thyroid autoimmunity. Higher FT3/FT4 ratio was associated with a mild increased risk of prediabetes (95% CI 1.09; 1.02-1.16). Compared with subjects in the lowest quartile of PTFQI, those in the highest quartile had lower risk of prediabetes (0.70; 95% CI, 0.58-0.84).

CONCLUSIONS

Decreased central sensitivity to thyroid hormones is associated with lower risk of prediabetes. This demonstrates the complex interaction between thyroid system and glucose metabolism. Future studies are warranted to confirm our findings and underlying mechanisms.

Free Thyroxine Levels are Associated with Cold Induced Thermogenesis in Healthy Euthyroid Individuals

Thyroid hormone (TH) is an important regulator of mammalian metabolism and facilitates cold induced thermogenesis (CIT) in brown adipose tissue (BAT). Profound hypothyroidism or hyperthyroidism lead to alterations in BAT function and CIT. In euthyroid humans the inter-individual variation of thyroid hormones is relatively large. Therefore, we investigated whether levels of free thyroxine (T4) or free triiodothyronine (T3) are positively associated with CIT in euthyroid individuals. We performed an observational study in 79 healthy, euthyroid volunteers (mean age 25.6 years, mean BMI 23.0 kg · m^-2). Resting energy expenditure (REE) was measured by indirect calorimetry during warm conditions (EE_warm) and after a mild cold stimulus of two hours (EE_cold). CIT was calculated as the difference between EE_cold and EE_warm. BAT activity was assessed by ¹⁸F-FDG-PET after a mild cold stimulus in a subset of 26 participants. EE_cold and CIT were significantly related to levels of free T4 (R² = 0.11, p=0.0025 and R² = 0.13, p=0.0011, respectively) but not to free T3 and TSH. Cold induced BAT activity was also associated with levels of free T4 (R² = 0.21, p=0.018). CIT was approximately fourfold higher in participants in the highest tertile of free T4 as compared to the lowest tertile. Additionally, free T4 was weakly, albeit significantly associated with outdoor temperature seven days prior to the respective study visit (R² = 0.06, p=0.037). These finding suggests that variations in thyroid hormone levels within the euthyroid range are related to the capability to adapt to cool temperatures and affect energy balance.

Increased Serum Adipocyte Fatty Acid-Binding Protein Levels Are Associated with Decreased Sensitivity to Thyroid Hormones in the Euthyroid Population

Background: Serum adipocyte fatty acid-binding protein (A-FABP) and thyroid hormones are closely associated with metabolic disorders; however, their relationship remains unknown. We aimed at investigating the associations of serum A-FABP levels with single and composite indices of the thyroid system. Methods: The study included 1057 community-based euthyroid participants (age range: 27-81 years) in Shanghai, among whom 601 were women. Serum free triiodothyronine (fT3), free thyroxine (fT4), and thyrotropin (TSH) were measured by electrochemical luminescence immunoassay. The thyroid feedback quantile-based index (TFQI), thyrotropin index (TSHI), and thyrotroph thyroxine resistance index (TT4RI) were calculated to evaluate central sensitivity to thyroid hormones. Peripheral sensitivity to thyroid hormones was evaluated by the fT3 to fT4 ratio (fT3/fT4). Enzyme-linked immunosorbent assay was used to measure serum A-FABP levels. Results: Serum A-FABP levels were 6.41 [95% confidence interval: 6.10-6.74] ng/mL among all subjects. Multiple cardiovascular metabolic risk factors were adjusted in the multivariate linear regression analysis and the multinomial logistic regression analysis (nonordinal). In both sexes, serum A-FABP levels were positively associated with fT4 (men: standardized β = 0.150, p = 0.001; women: standardized β = 0.218, p < 0.001), TFQI (men: standardized β = 0.119, p = 0.009; women: standardized β = 0.165, p < 0.001), and TSHI (men: standardized β = 0.108, p = 0.017; women: standardized β = 0.114, p = 0.005); while they were negatively associated with fT3/fT4 (men: standardized β = -0.122, p = 0.008; women: standardized β = -0.129, p = 0.001). Serum A-FABP levels were not associated with fT3, TSH, or TT4RI. Compared with the first quartile group of TFQI, for every 10 ng/mL increase in A-FABP, the odds ratio (OR) for the third quartile group of TFQI was 2.213 in women (p = 0.035); the ORs for the fourth quartile group of TFQI were 2.614 in men (p = 0.022) and 3.425 in women (p = 0.002). Conclusions: In a euthyroid population, increased serum A-FABP levels were associated with decreased sensitivity to thyroid hormones, suggesting that A-FABP may mediate the "cross-talk" between adipose tissue and the thyroid system.

Clinical Parameters Are More Likely to Be Associated with Thyroid Hormone Levels than with Thyrotropin Levels: A Systematic Review and Meta-Analysis

Background: Though the functional states of other endocrine systems are not defined on the basis of levels of controlling hormones, the assessment of thyroid function is based on levels of the controlling hormone thyrotropin (TSH). We, therefore, addressed the question as to whether levels of thyroid hormones [free thyroxine (fT4), total triiodothyronine (TT3)/free triiodothyronine (fT3)], or TSH levels, within and beyond the reference ranges, provide the better guide to the range of clinical parameters associated with thyroid status. Methods: A PubMed/MEDLINE search of studies up to October 2019, examining associations of levels of thyroid hormones and TSH, taken simultaneously in the same individuals, with clinical parameters was performed. We analyzed atrial fibrillation, other cardiac parameters, osteoporosis and fracture, cancer, dementia, frailty, mortality, features of the metabolic syndrome, and pregnancy outcomes. Studies were assessed for quality by using a modified Newcastle-Ottawa score. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed. A meta-analysis of the associations was performed to determine the relative likelihood of fT4, TT3/fT3, and TSH levels that are associated with the clinical parameters. Results: We identified 58 suitable articles and a total of 1880 associations. In general, clinical parameters were associated with thyroid hormone levels significantly more often than with TSH levels-the converse was not true for any of the clinical parameters. In the 1880 considered associations, fT4 levels were significantly associated with clinical parameters in 50% of analyses. The respective frequencies for TT3/fT3 and TSH levels were 53% and 23% (p < 0.0001 for both fT4 and TT3/fT3 vs. TSH). The fT4 and TT3/fT3 levels were comparably associated with clinical parameters (p = 0.71). More sophisticated statistical analyses, however, indicated that the associations with TT3/fT3 were not as robust as the associations with fT4. Conclusions: Thyroid hormones levels, and in particular fT4 levels, seem to have stronger associations with clinical parameters than do TSH levels. Associations of clinical parameters with TSH levels can be explained by the strong negative population correlation between thyroid hormones and TSH. Clinical and research components of thyroidology currently based on the measurement of the thyroid state by reference to TSH levels warrant reconsideration.

Sex-influenced association between free triiodothyronine levels and poor glycemic control in euthyroid patients with type 2 diabetes mellitus

OBJECTIVE

The study investigated the association between free triiodothyronine (FT3) and poor glycemic control with different definitions in euthyroid patients with type 2 diabetes mellitus (T2DM).

METHODS

This was a cross-sectional study which included 2172 patients from National Metabolic Management Center in Ruijin Hospital. The association between thyroid function and glycated hemoglobin A1c (HbA1c) was determined by multiple liner regression models. The association between FT3 and poor glycemic control was further determined by binary logistic regression models. Two definitions of poor glycemic control (HbA1c ≥ 7% and HbA1c ≥ 8%) were applied when we analyzed the association.

RESULTS

Prevalence of HbA1c ≥ 7% and HbA1c ≥ 8% were 63.8% and 39.3%, respectively. After adjusting for confounding factors, FT3, rather than free tetraiodothyronine (FT4) or thyroid stimulating hormone (TSH), was independently associated with HbA1c (β = -0.104, P = 0.002). Further analysis after gender stratification showed that the association was only found in males (β = -0.164, P < 0.001). We further analyzed the association between FT3 quartiles and poor glycemic control. FT3 quartiles were not significantly associated with the risk of HbA1c ≥ 7% before and after adjusting for confounding factors in both genders. FT3 quartiles were negatively associated with the risk of HbA1c ≥ 8% only in males, independent of traditional risk factors for poor glycemic control (P for trend = 0.030).

CONCLUSIONS

FT3 in the reference range was significantly associated with reduced risk of HbA1c ≥ 8% in males, independent of traditional risk factors for poor glycemic control.

Urinary miR-3137 and miR-4270 as potential biomarkers for diabetic kidney disease

Background

As one of the most prevalent diagnostic indicators of diabetic kidney disease (DKD), albumin‐to‐creatinine ratio (ACR) shows considerably limited predictive power in clinical application. We analyzed microarray expression profiling of urine to seek for differentially expressed miRNAs for potential biomarkers of DKD.

Methods

Urine samples from type 2 diabetes mellitus (T2DM) patients with (30 mg/g < ACR < 300 mg/g, DKD group) or without DKD (ACR < 30 mg/g, DM group) were collected for miRNA microarray analysis. The differentially expressed miRNAs were screened by bioinformatics analysis and validated by quantitative real‐time PCR. Target genes of differentially expressed miRNAs were predicted in miRDB, Targetscan, and microRNA.org databases. We also conducted the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathways analysis to explore for potential mechanisms in DKD.

Results

Nine miRNAs were down‐regulated and seventeen miRNAs were up‐regulated in DKD group, compared to DM group. The levels of miR‐3137 and miR‐4270 in DKD group were 0.670 ± 0.505 and 2.116 ± 1.762 times than those in DM group, respectively, showing great significance. A total of 1076 target genes were simultaneously predicted by miRDB, Targetscan, and microRNA.org databases. According to the GO analysis results, disorders of endomembrane system may be one of the major pathological changes in DKD. In addition, Rap 1 signaling pathway is also altered obviously in DKD, discovered by the KEGG analysis.

Conclusion

MiR‐3137 and miR‐4270 show the potential for urinary biomarkers of DKD. The pathological changes of DKD may be related to disorders of endomembrane system and alternation of Rap1 signaling pathway.

Thyroid Hormone Changes in Euthyroid Patients with Diabetes

BACKGROUND

Thyroid dysfunction is associated with diabetes, but it is unclear if the thyroid hormone levels change in euthyroid adults with diabetes.

OBJECTIVE

To investigate the association between thyroid hormone levels and diabetes in euthyroid adults.

METHODS

Among the euthyroid adults who underwent health examination in West China Hospital of Sichuan University in 2016, patients with diabetes were identified according to the medical history, fasting blood glucose and HbA1c. Age and sex matched controls were identified from the population. The patients with diabetes group was further divided into two subgroups: patients with newly diagnosed diabetes (NDD) and with previously diagnosed diabetes (PDD). Independent t-test and multivariate logistic regression models were used to investigate the difference in the levels of thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and the ratio of FT4/FT3 between groups.

RESULTS

We included 32,557 participants, 2,271 with diabetes. Compared to the adults without diabetes, the odds ratios (ORs) per one unit elevation of TSH, FT4, FT4/FT3 ratio and FT3 in patients with diabetes were 0.88 [95% confidence interval (CI): 0.82-0.95], 1.11 (95% CI: 1.08-1.14), 2.05 (95% CI: 1.81-2.32) and 0.85 (95% CI: 0.78-0.93), respectively. Compared to the NDD group, the ORs per one unit elevation of TSH, FT4, FT4/FT3 ratio and FT3 of the PDD group were 0.81 (95% CI: 0.71-0.92), 1.08 (95% CI: 1.04-1.12), 1.76 (95% CI: 1.49-2.08) and 1.01 (95% CI: 0.92-1.12), respectively.

CONCLUSION

In euthyroid adults, diabetes was associated with increased FT4/FT3 ratio, which is linked to the peripheral turnover of the thyroid hormones.

Thyroid Dysfunction and Diabetes Mellitus: Two Closely Associated Disorders

Thyroid dysfunction and diabetes mellitus are closely linked. Several studies have documented the increased prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. This review critically discusses the different underlying mechanisms linking type 1 and 2 diabetes and thyroid dysfunction to demonstrate that the association of these two common disorders is unlikely a simple coincidence. We assess the current state of knowledge on the central and peripheral control of thyroid hormone on food intake and glucose and lipid metabolism in target tissues (such as liver, white and brown adipose tissue, pancreatic β cells, and skeletal muscle) to explain the mechanism linking overt and subclinical hypothyroidism to type 2 diabetes and metabolic syndrome. We also elucidate the common susceptibility genes and the pathogenetic mechanisms contributing to the autoimmune mechanism involved in the onset of type 1 diabetes mellitus and autoimmune thyroid disorders. An untreated thyroid dysfunction can impair the metabolic control of diabetic patients, and this association can have important repercussions on the outcome of both of these disorders. Therefore, we offer recommendations for the diagnosis, management, and screening of thyroid disorders in patients with diabetes mellitus, including the treatment of diabetic patients planning a pregnancy. We also discuss the major causes of failure to achieve an optimal management of thyroid dysfunction in diabetic patients and provide recommendations for assessing and treating these disorders during therapy with antidiabetic drugs. An algorithm for a correct approach of these disorders when linked is also provided.

Thyroid-stimulating hormone levels in the normal range and incident type 2 diabetes mellitus

AIM

To evaluate the relationship between thyroid-stimulating hormone (TSH) levels within the normal range and the risk of type 2 diabetes mellitus (T2DM) in a cohort of patients at high cardiovascular risk, and to perform a systematic review and meta-analysis of previous studies.

METHODS

We included 5542 patients without T2DM from the prospective Secondary Manifestations of ARTerial disease study with TSH levels between 0.35 and 5.0 mIU/L without anti-thyroid medication or thyroid-hormone replacement therapy. Cox regression was used to investigate the relationship between baseline plasma TSH levels and incident T2DM. MEDLINE, EMBASE, and Cochrane were searched for prospective cohorts assessing TSH and incident T2DM. Hazard ratios (HR) from included prospective cohort studies were pooled using a random-effects model.

RESULTS

In patients at high cardiovascular risk, higher plasma TSH levels in the normal range were not associated [HR 1.07 per mIU/L increase in TSH (95% confidence interval (95% CI) 0.95-1.22)] with an increased risk of T2DM, adjusted for age, sex, smoking, total and HDL cholesterol, and triglycerides. In the meta-analysis involving three prospective cohort studies, including the present study, including 29,791 participants with 1930 incident events, there was no relation between plasma TSH levels in the normal range and incident T2DM [pooled HR 1.06 (95% CI 0.99-1.14)].

CONCLUSION

There is no apparent relation between plasma TSH levels in the normal range and incident T2DM in patients at high cardiovascular risk.

High-normal serum thyrotropin levels and increased glycemic variability in type 2 diabetic patients

PURPOSE

High-normal thyrotropin (TSH) is related to reduced insulin sensitivity and may contribute to glycemic disorders in diabetes. We investigated the relationship between normal serum TSH levels and glycemic variability in euthyroid type 2 diabetic patients.

METHODS

A total of 432 newly diagnosed type 2 diabetic patients with euthyroid function and normal serum TSH levels were recruited between March 2013 and February 2017. Insulin sensitivity was evaluated by the Matsuda index (ISI_Matsuda) following a 75-g oral glucose tolerance test. Multiple glycemic variability indices, including the mean amplitude of glycemic excursions (MAGE), mean of daily differences (MODD), and standard deviation of glucose (SD), were calculated from glucose data obtained with a continuous glucose monitoring system. Average glucose accessed by 24-h mean glucose (24-h MG) was also calculated.

RESULTS

A normal serum TSH level was positively correlated with MAGE, MODD, SD, and 24-h MG (r = 0.206, 0.178, 0.186, and 0.132, respectively, p < 0.01). After adjusting for somatometric parameters, lipid profiles, ISI_Matsuda, and HbA1c via multiple linear regression analysis, mean differences [B(95% CI)] in MAGE, MODD, SD, and 24-h MG between the patients in the lowest and highest quartiles of TSH levels were 0.128(0.031, 0.226), 0.085(0.022, 0.148), 0.039(0.001, 0.078), and 0.002(-0.264, 0.267) mmol/L, respectively. High-normal TSH was independently associated with MAGE, MODD, and SD, but not 24-h MG.

CONCLUSIONS

High-normal serum TSH is a significant additional risk factor for increased glycemic variability in type 2 diabetic patients.

TSH oscillations in young patients with type 1 diabetes may be due to glycemic variability

PURPOSE

A relationship between thyroid dysfunction and diabetes mellitus has been described by several authors but the role of glycemic variability is still unclear. We planned the present study to evaluate the influence of glycemic variability on thyroid hormones and TSH concentrations in patients with type 1 diabetes mellitus (T1DM).

METHODS

Seventy-seven young patients with T1DM were enrolled and evaluated for basal glucose concentrations, HbA1c, thyroid hormones and TSH concentrations. Glucose variability was investigated by considering the standard deviation of blood glucose readings and by calculating the mean amplitude of glycemic excursions and continuous overlapping net glycemic action (CONGA). The low (LBGI) and high (HBGI) blood glucose indices were also calculated. The correlations between TSH, thyroid hormones, glycemia and HbA1c were studied in patients and in controls, whereas those between TSH, thyroid hormones and indices of glucose variability only in patients.

RESULTS

No correlations were observed in T1DM patients between free thyroid hormones and glycemic values, HbA1c and indices of glucose variability, while an inverse correlation was observed between TSH levels and glycemic values (r = -0.27; p = 0.01), CONGA index (r = -0.35; p = 0.001) and HBGI (r = -0.28; p = 0.01) but not with HbA1c (r = -0.1; p = 0.47).

CONCLUSIONS

Our results suggest a direct action of glycemic excursions on TSH secretion, regardless of variations of thyroid hormone concentrations. Thus, the evaluation of thyroid function through the assay of TSH concentrations in these patients should be made, if possible, by multiple samples on patients in euglycemic state to avoid underestimation or overestimation of thyroid dysfunction due to a wrong diagnosis of euthyroidism or dysthyroidism with consequent inappropriate choice of therapeutic options.

Hormetic effect of triiodothyronine in metabolically healthy obese persons

PURPOSE

Metabolically healthy obese is the designation for a subgroup of obese individuals with normal metabolic features. However, metabolically healthy obese individuals are prone to developing metabolic syndrome. Serum triiodothyronine (T3) levels are associated with various metabolic risk factors including obesity. Therefore, this longitudinal study aimed to explore the possible correlation between serum T3 concentration and the onset of MetS in metabolically healthy obese persons.

METHODS

A retrospective analysis of 992 euthyroid metabolically healthy obese subjects who underwent yearly health checkups over 6 years was performed. The risk of developing MetS was analyzed according to baseline T3 concentration, as both tertiles and continuous values, using Cox regression analysis. Serum T3 concentration at the end of the study was further analyzed according to the final metabolic phenotype.

RESULTS

The incidence of MetS was 464 cases (46.8%) during a median 3.3 years of follow-up (3168.2 person-years). The hazard ratio for incident MetS enhanced with increasing T3 concentration in both the crude and adjusted models. Higher baseline serum T3 levels were associated with unfavorable metabolic parameters. However, over the course of the study, serum T3 concentration significantly increased in subjects who sustained metabolically healthy phenotypes compared to baseline value, while it significantly decreased in the subjects who developed MetS.

CONCLUSIONS

Serum T3 concentrations exhibit distinct associations with development of metabolic syndrome in euthyroid metabolically healthy obese persons, but its increment during follow-up maintained metabolically healthy state. These findings suggest that serum T3 modulation might be an adaptive process to protect against metabolic deterioration.

Association of high normal HbA1c and TSH levels with the risk of CHD: a 10-year cohort study and SVM analysis

This study aimed to determine the association between the clinical reference range of serum glycated hemoglobin A1c (HbA1c) and thyrotropin (TSH) and the risk of coronary heart disease (CHD) in non-diabetic and euthyroid patients. We examined baseline HbA1c and TSH in 538 healthy participants, and then analyzed the associations and potential value of these indicators for predicting CHD using Cox proportional hazard and support vector machine analyses. During the median follow-up of 120 months, 39 participants later developed CHD. The baseline HbA1c and TSH within the reference range were positively associated with CHD risk. No correlation and interaction were found between the baseline HbA1c and TSH for the development of CHD. Disease event-free survival varied among participants with different baseline HbA1c quintiles, whereas disease event-free survival was similar for different TSH tertiles. The combination of these baselines showed sensitivity of 87.2%, specificity of 92.7%, and accuracy of 92.3% for identifying the participants who will later develop CHD. Relatively high but clinically normal HbA1c and TSH levels may increase the risk of CHD. Therefore, the combination of these indicators can serve as a biomarker for identifying healthy individuals from those who would later develop CHD.

TSH increment and the risk of incident type 2 diabetes mellitus in euthyroid subjects

PURPOSE

Thyroid function is known to influence glucose metabolism, and thyroid-stimulating hormone is the most useful parameter in screening for thyroid dysfunction. Therefore, the aim of this study was to investigate the incidence of type 2 diabetes according to baseline thyroid-stimulating hormone level and thyroid-stimulating hormone change in euthyroid subjects.

METHODS

We identified and enrolled 17,061 euthyroid subjects without diabetes among participants who had undergone consecutive thyroid function tests between 2006 and 2012 as a part of yearly health check-up program. Thyroid-stimulating hormone changes were determined by subtracting baseline thyroid-stimulating hormone level from thyroid-stimulating hormone level at 1 year before diagnosis of diabetes or at the end of follow-up in subjects who did not develope diabetes.

RESULTS

During 84,595 person-years of follow-up, there were 956 new cases of type 2 diabetes. Cox proportional hazards models showed the risk of incident type 2 diabetes was significantly increased with each 1 μIU/mL increment in TSH after adjustment for multiple confounding factors (hazard ratio = 1.13, 95% confidence interval: 1.07-1.20, P < 0.001). Compared with individuals in the lowest tertile (-4.08 to 0.34 μIU/mL), those in the highest thyroid-stimulating hormone change tertile (0.41-10.84 μIU/mL) were at greater risk for incident type 2 diabetes (hazard ratio = 1.25, 95% confidence interval: 1.05-1.48, P for trend = 0.011). However, baseline thyroid-stimulating hormone level and tertile were not associated with the risk for diabetes.

CONCLUSIONS

Prominent increase in thyroid-stimulating hormone concentration can be an additional risk factor for the development of type 2 diabetes in euthyroid subjects.

Association of Vitamin D Deficiency and Thyroid Function in Postmenopausal Women

Pupose: Although there are reports of vitamin D (VitD) insufficiency in immune-mediated hypothyroidism, an association between VitD and thyroid-stimulating hormone (TSH) levels has yet to be shown. We aim to examine VitD and TSH levels among postmenopausal women, as both conditions are more prevalent in elderly women. Methods: The clinic records of postmenopausal women during their routine maintenance visits were reviewed. All patients were examined for the symptoms related to thyroid function and osteoporosis. Participants were divided into three subgroups according to their TSH levels (below <0.5 mIU/L, 0.51-4.0 mIU/L and >4.0 mIU/L). Patient characteristics and VitD levels were compared between these subgroups. Multivariate linear regression model was constructed using serum VitD and serum TSH as the dependent variables to identify factors independently associated with these laboratory values. Results: Two-hundred and nighty nine postmenopausal women were included. Average age was 62.2±7.5 years old. VitD was insufficient (10-30 ng/mL) in 12.0% and deficient (<10 ng/mL) in 60.9% of the participants. In 11.3%, TSH was low and in 7.6% of women, TSH was high, while the remaining 80.1%, had normal TSH levels. Subjects with low TSH had significantly higher VitD concentrations (34.2±29.1 ng/mL) compared to the other two groups (P-value: 0.039). In multivariate regression analysis, TSH was not a contributing factor, as age was the only significant predictor of VitD levels. Meanwhile, no predictor (including age and VitD) was identified for TSH levels in linear regression analysis. Conclusion: Age was the only independent predictor of serum VitD in this study population. Though suppressed TSH was associated with higher VitD levels, the association was not linear between TSH and VitD in postmenopausal women.