The optimal healthy ranges of thyroid function defined by the risk of cardiovascular disease and mortality: systematic review and individual participant data meta-analysis

Associations of reverse triiodothyronine serum levels with anxiety, depression, and health related quality of life after experiencing acute ischemic stroke

Aim

This study intended to explore associations of reverse triiodothyronine (rT3) with emotional disturbances and health-related quality of life (HRQoL) after experiencing acute ischemic stroke (AIS).

Materials and methods

Serum samples from individuals with AIS were collected on admission to three Lithuania stroke centers and investigated for free tetraiodothyronine, free triiodothyronine (fT3), rT3, and thyroid stimulating hormone levels. At discharge, emotional disturbance was evaluated using the Hospital Depression and Anxiety Scale (HADS), and HRQoL using the EQ-5D-5L scale.

Results

Analyses included 159 individuals (59.7% male and 40.3% female; mean (SD) aged 66.4 [10.3] years), 52.83% of which showed increased rT3 levels upon admission. After adjustment for age, sex, National Institutes of Health Stroke Scale scores, previous stroke, modified Rankin Scale before AIS ≤ 2, and diabetes mellitus, multivariable linear regression revealed negative associations of rT3 with HADS total score (β = -0.163; p = 0.046) and HADS-D subscale score (β = -0.187; p = 0.019). Analyses supported a positive relationship between the fT3 ratio to rT3 with HADS-D score (β = 0.157; p = 0.046) and rT3, rT3 × fT3 product with EQ-5D index score (β = 0.157; p = 0.044 and β = 0.179; p = 0.023, respectively).

Conclusion

We found that individuals who experienced AIS and had higher levels of rT3 at hospital admission had less emotional disturbance and better HRQoL when discharged.

Subclinical Hyperthyroidism and Cardiovascular Disease

Background: In this narrative review, we assess published data on subclinical hyperthyroidism (SCHyper) and its association with cardiovascular disease (CVD) in the general population. Summary: We present data on the risk of SCHyper in relation to CVD outcomes, including atrial fibrillation (AF), heart failure, stroke, coronary heart disease (CHD), major adverse cardiac events (MACE), CVD mortality, and all-cause mortality. Evidence indicates that SCHyper is associated with an elevated risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. SCHyper appears to have little association with stroke risk and has shown conflicting results regarding CHD risk. Regarding the degree of serum TSH suppression, evidence shows a higher risk of CVD in SCHyper individuals with suppressed TSH (<0.1 mIU/L) compared with those with low TSH (0.1-0.4 mIU/L). Despite evidence that older individuals are inherently at a higher risk for CVD, no studies have yet demonstrated an age-related increase in the relative risk of CVD in SCHyper. Conclusion: The studies indicate that SCHyper is associated with an increased risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. Considering the importance of the degree of serum TSH suppression and age as risk factors for CVD, treatment decisions should be individualized based on their specific risk factors.

Defining Gestational Thyroid Dysfunction Through Modified Nonpregnancy Reference Intervals: An Individual Participant Meta-analysis

BACKGROUND

Establishing local trimester-specific reference intervals for gestational TSH and free T4 (FT4) is often not feasible, necessitating alternative strategies. We aimed to systematically quantify the diagnostic performance of standardized modifications of center-specific nonpregnancy reference intervals as compared to trimester-specific reference intervals.

METHODS

We included prospective cohorts participating in the Consortium on Thyroid and Pregnancy. After relevant exclusions, reference intervals were calculated per cohort in thyroperoxidase antibody-negative women. Modifications to the nonpregnancy reference intervals included an absolute modification (per .1 mU/L TSH or 1 pmol/L free T4), relative modification (in steps of 5%) and fixed limits (upper TSH limit between 3.0 and 4.5 mU/L and lower FT4 limit 5-15 pmol/L). We compared (sub)clinical hypothyroidism prevalence, sensitivity, and positive predictive value (PPV) of these methodologies with population-based trimester-specific reference intervals.

RESULTS

The final study population comprised 52 496 participants in 18 cohorts. Optimal modifications of standard reference intervals to diagnose gestational overt hypothyroidism were -5% for the upper limit of TSH and +5% for the lower limit of FT4 (sensitivity, .70, CI, 0.47-0.86; PPV, 0.64, CI, 0.54-0.74). For subclinical hypothyroidism, these were -20% for the upper limit of TSH and -15% for the lower limit of FT4 (sensitivity, 0.91; CI, 0.67-0.98; PPV, 0.71, CI, 0.58-0.80). Absolute and fixed modifications yielded similar results. CIs were wide, limiting generalizability.

CONCLUSION

We could not identify modifications of nonpregnancy TSH and FT4 reference intervals that would enable centers to adequately approximate trimester-specific reference intervals. Future efforts should be turned toward studying the meaningfulness of trimester-specific reference intervals and risk-based decision limits.

Hypothyroidism

Hypothyroidism, the deficiency of thyroid hormone, is a common condition worldwide. It affects almost all body systems and has a wide variety of clinical presentations from being asymptomatic to, in rare cases, life threatening. The classic symptoms of hypothyroidism include fatigue, lethargy, weight gain, and cold intolerance; however, these symptoms are non-specific and the diagnosis is typically made on biochemical grounds through serum thyroid function tests. The most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto's thyroiditis), although other causes, including drugs (such as amiodarone, lithium, and immune checkpoint inhibitors), radioactive-iodine treatment, and thyroid surgery, are frequent. Historically, severe iodine deficiency was the most common cause. Reference ranges for thyroid function tests are based on fixed percentiles of the population distribution, but there is increasing awareness of the need for more individualised reference intervals based on key factors such as age, sex, and special circumstances such as pregnancy. Levothyroxine monotherapy is the standard treatment for hypothyroidism; it is safe and inexpensive, restores thyroid function tests to within the reference range, and improves symptoms in the majority of patients. However, 10% of patients have persistent symptoms of ill health despite normalisation of thyroid function tests biochemically and a substantial proportion of patients on levothyroxine have thyroid-stimulating hormone concentrations outside the reference range. Ongoing symptoms despite levothyroxine treatment has led to some patients using liothyronine or desiccated thyroid extract. Taken together, these factors have led to intense debate around the treatment thresholds and treatment strategies for hypothyroidism. In this Seminar, we review the epidemiology, genetic determinants, causes, and presentation of hypothyroidism; highlight key considerations and controversies in its diagnosis and management; and provide future directions for research.

Metabolic Syndrome, Thyroid Dysfunction, and Cardiovascular Risk: The Triptych of Evil

The triad formed by thyroid dysfunction, metabolic syndrome (MetS), and cardiovascular (CV) risk forms a network with many connections that aggravates health outcomes. Thyroid hormones (THs) play an important role in glucose and lipid metabolism and hemodynamic regulation at the molecular level. It is noteworthy that a bidirectional association between THs and MetS and their components likely exists as MetS leads to thyroid dysfunction, whereas thyroid alterations may cause a higher incidence of MetS. Thyroid dysfunction increases insulin resistance, the circulating levels of lipids, in particular LDL-C, VLDL-C, and triglycerides, and induces endothelial dysfunction. Furthermore, THs are important regulators of both white and brown adipose tissue. Moreover, the pathophysiological relationship between MetS and TH dysfunction is made even tighter considering that these conditions are usually associated with inflammatory activation and increased oxidative stress. Therefore, the role of THs takes place starting from the molecular level, then manifesting itself at the clinical level, through an increased risk of CV events in the general population as well as in patients with heart failure or acute myocardial infarction. Thus, MetS is frequently associated with thyroid dysfunction, which supports the need to assess thyroid function in this group, and when clinically indicated, to correct it to maintain euthyroidism. However, there are still several critical points to be further investigated both at the molecular and clinical level, in particular considering the need to treat subclinical dysthyroidism in MetS patients.

Establishment of precise prevention strategies for the occurrence and progression of coronary atherosclerotic heart disease using machine learning

Background

Coronary atherosclerotic heart disease (CHD) is highly prevalent in Northwest China; however, effective preventive measures are limited. This study aimed to develop metabolic risk models tailored for the primary and secondary prevention of CHD in Northwest China.

Methods

This hospital-based cross-sectional study included 744 patients who underwent coronary angiography. Data on demographic characteristics, comorbidities, and serum biochemical indices of the participants were collected. Three machine learning algorithms-recursive feature elimination, random forest, and least absolute shrinkage and selection operator-were employed to construct risk models. Model validation was performed using receiver operating characteristic and calibration curves, and the optimal cutoff values for significant risk factors were determined.

Results

The predictive model for CHD onset included sex, overweight/obesity, and hemoglobin A1c (HbA1c) levels. For CHD progression to multiple coronary artery disease, the model included age, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and HbA1c levels. The model predicting an increased coronary Gensini score included sex, overweight/obesity, TC, LDL-C, high-density lipoprotein cholesterol, lipoprotein(a), and HbA1c levels. Notably, the optimal cutoff values for HbA1c and lipoprotein(a) for determining CHD progression were 6 % and 298 mg/L, respectively.

Conclusions

Robust metabolic risk models were established, offering significant value for both the primary and secondary prevention of CHD in Northwest China. Weight loss, strict hyperglycemic control, and improvement in dyslipidemia may help prevent or delay the occurrence and progression of CHD in this region.

Relationship between preoperative FT3 levels and new-onset atrial fibrillation after off-pump coronary artery bypass grafting

Background

Postoperative atrial fibrillation (POAF) is the most common arrhythmia after cardiac surgery. While thyroid dysfunction can predict POAF, the association between preoperative serum free triiodothyronine (FT3) levels and POAF in patients undergoing off-pump coronary artery bypass (OPCAB) grafting remains unclear. This study aimed to investigate the relationship between preoperative FT3 levels and POAF in OPCAB patients.

Methods

This prospective observational study included patients with sinus rhythm and no history of atrial fibrillation or thyroid disease who underwent OPCAB and FT3 testing at the Tianjin Chest Hospital from June 2021 to March 2023. The relationship between FT3 level and POAF was evaluated using restricted cubic spline. Cox proportional hazards regression models were used to analyze the associations between FT3 concentration categories [low T3 syndrome (LT3S) (FT3 below the normal range), low normal FT3 (3.10-4.59 pmol/L), high normal FT3 (4.60-6.80 pmol/L)] and POAF, adjusting for potential confounders. Stratified analyses were performed to assess effect modification by gender and age (<60 vs. ≥60 years old).

Results

Among 875 patients, 259 (29.6%) developed POAF within 2 days after surgery. Restricted cubic spline analysis showed an S-shaped association between FT3 concentration and POAF risk. Compared to the low normal FT3 group, LT3S was associated with an increased risk of POAF [hazard ratio (HR), 1.41; 95% confidence interval (CI): 1.90-2.19], while high normal FT3 was associated with a decreased risk (HR, 0.72; 95% CI: 0.51-0.99). The association between FT3 and increased POAF risk was more pronounced in patients aged ≥60 years (HR, 1.41; 95% CI: 1.89-2.22).

Conclusions

Preoperative FT3 levels most likely could predict POAF risk after OPCAB, especially in patients aged 60 years and older. Measuring FT3 preoperatively may identify high-risk patients benefiting from close monitoring and prophylactic treatment. Further investigation of thyroid hormone replacement therapy for LT3S is warranted.

Associations of TSH, free T3, free T4, and conversion ratio with incident hypertension: results from the prospective Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Objective

To evaluate the association of TSH, free T3 (FT3), free T4 (FT4), and conversion (FT3:FT4) ratio values with incident hypertension.

Materials and methods

The study included data from participants of the ELSA-Brasil study without baseline hypertension. Serum TSH, FT4 and FT3 levels, and FT3:FT4 ratio values were assessed at baseline, and incident hypertension (defined by blood pressure levels ≥ 140/90 mmHg) was estimated over a median of 8.2 years of follow-up. The risk of incident hypertension was evaluated considering a 1-unit increase in TSH, FT4, FT3, and conversion ratio values and after dividing these variables into quintiles for further analysis using Poisson regression with robust variance. The results are presented as relative risks (RR) and 95% confidence intervals (CIs) before and after adjustment for multiple variables.

Results

The primary analysis incorporated data from 5,915 euthyroid individuals, and the secondary analysis combined data from all euthyroid individuals, 587 individuals with subclinical hypothyroidism, and 31 individuals with subclinical hyperthyroidism. The rate of incident hypertension was 28% (95% CI: 27%-29.3%). The FT4 levels in the first quintile (0.18-1.06 ng/dL) were significantly associated with incident hypertension (RR: 1.03, 95% CI: 1.01-1.06) at follow-up. The association between FT4 levels in the first quintile and incident hypertension was also observed in the analysis of combined data from euthyroid individuals and participants with subclinical thyroid dysfunction (RR: 1.04, 95% CI: 1.01-1.07). The associations were predominantly observed with systolic blood pressure levels in euthyroid individuals. However, in the combined analysis incorporating euthyroid participants and individuals with subclinical thyroid dysfunction, the associations were more pronounced with diastolic blood pressure levels.

Conclusion

Low FT4 levels may be a mild risk factor for incident hypertension in euthyroid individuals and persons with subclinical thyroid dysfunction.

Causal association of TSH with ischemic heart diseases and heart failure: A 2-sample Mendelian randomization study

Thyroid dysfunction is associated with the risk of cardiovascular disease; however, whether plasma thyroid-stimulating hormone (TSH) levels in subjects with euthyroidism affect the risk of cardiovascular disease remains unclear. This study aimed to investigate the causal association between plasma TSH levels and cardiovascular diseases, particularly ischemic heart disease and heart failure (HF). Summary statistics from the Integrative Epidemiology Unit Open genome-wide association studies Project and FinnGen consortium were used to investigate the causal relationship between plasma TSH levels and the risk of cardiovascular diseases. Two-sample Mendelian randomization analysis using inverse-variance weighting as the primary method was performed. The MR Pleiotropy RESidual Sum and Outlier and leave-one-out methods were used to ensure the robustness of our findings. Genetically determined plasma TSH levels were associated with major coronary heart disease events (OR 1.0557, 95% CI 1.0141-1.0991), all-cause HF (OR 0.9587, 95% CI 0.9231-0.9956), and HF + non-ischemic cardiomyopathy (OR 0.9318, 95% CI 0.8786-0.9882). After the Bonferroni correction, the causation described above disappeared. In the secondary analysis, genetically determined higher TSH levels were associated with a higher risk for unstable angina pectoris (OR 1.0913, 95% CI 1.0350-1.1507), but were associated with a lower risk for HF + overweight (OR 0.9265, 95% CI 0.8821-0.9731). These results were further validated using sensitivity analysis. Our findings show that increased plasma TSH levels in patients with euthyroidism may increase the risk of unstable angina pectoris but reduce the risk of HF in overweight patients. This evidence indicates that plasma TSH levels may need to be carefully controlled in specific patients.

The Rotterdam Study. Design update and major findings between 2020 and 2024

The Rotterdam Study is a population-based cohort study, started in 1990 in the district of Ommoord in the city of Rotterdam, the Netherlands, with the aim to describe the prevalence and incidence, unravel the etiology, and identify targets for prediction, prevention or intervention of multifactorial diseases in mid-life and elderly. The study currently includes 17,931 participants (overall response rate 65%), aged 40 years and over, who are examined in-person every 3 to 5 years in a dedicated research facility, and who are followed-up continuously through automated linkage with health care providers, both regionally and nationally. Research within the Rotterdam Study is carried out along two axes. First, research lines are oriented around diseases and clinical conditions, which are reflective of medical specializations. Second, cross-cutting research lines transverse these clinical demarcations allowing for inter- and multidisciplinary research. These research lines generally reflect subdomains within epidemiology. This paper describes recent methodological updates and main findings from each of these research lines. Also, future perspective for coming years highlighted.

Association of sensitivity to thyroid hormones with all-cause mortality in euthyroid US adults: A nationwide cohort study

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 quartile 4th (Q4) had lower all-cause mortality than those in quartile 1st (Q1) of FT3/FT4 ratio (OR 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 (OR 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.