Thyroid function and cognitive decline in the MRC Cognitive Function and Ageing Study

Thyroid Function and Brain Structure: Insight from a Mendelian Randomization Study

INTRODUCTION

Thyroid hormones play a critical role in brain development. However, the precise causal associations between thyroid function and structural changes in specific brain regions remain uncertain.

METHODS

We applied the univariate Mendelian randomization (UVMR) method to assess the causal effects of thyroid function on brain structure. Genome-wide association study (GWAS) data on thyroid-related traits from the ThyroidOmics Consortium including free thyroxine (FT4), free tri-iodothyronine (FT3), thyroid-stimulating hormone (TSH), FT3/FT4 ratio, as well as dichotomized high and low TSH levels were used as exposures. GWAS data on cortical thickness, surface area, and volume of subcortical structures served as outcomes. Inverse variance weighted was the main estimate method. Subsequently, multivariable MR (MVMR) was conducted to validate significant causal associations identified in UVMR.

RESULTS

UVMR analysis demonstrated a statistically significant inverse association between genetically predicted FT4 and putamen volume (β = -71.91 mm3, 95% confidence interval: -112.11 mm3 to -31.71 mm3, p = 4.54 × 10-4). The findings were robust in sensitivity analysis. MVMR analysis further confirmed a persistent causal relationship between FT4 and putamen volume after adjusting for FT3, TSH, and neuropsychiatric disorders. Functional enrichment analyses indicated the pathways by which FT4 influences putamen volume may be related to the thyroid hormone signaling pathway, sodium-independent organic anion transport, and Rap1 signaling pathway.

CONCLUSION

MR analysis provides evidence for causal relationships between thyroid function and brain structural alterations, particularly highlighting the impact of FT4 on putamen volume. Further research is warranted to elucidate the underlying mechanisms by which thyroid hormones modulate brain structure.

Thyroid Functions and Cognitive Decline in the Elderly

Background The maintenance of cognitive health depends on thyroid hormones, and it is becoming more widely acknowledged that thyroid hormone issues may be a factor in cognitive decline in the aged. Objective This study aimed to investigate the association between thyroid hormone levels and cognitive decline among elderly individuals, considering the influence of age-related factors and comorbidities. Methodology Over the course of two years, 218 adults 60 years of age and older with clinically diagnosed hypothyroidism or subclinical thyroid disease were included in a prospective observational research. Serum levels of thyroid-stimulating hormone (TSH), free thyroxine (T4), and free triiodothyronine (T3) were measured at baseline and at 6, 12, 18, and 24-month intervals to evaluate thyroid function. The Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) were used to assess cognitive function at the same intervals. Factors linked to cognitive deterioration were identified using multivariate regression analysis. Results The study found that TSH levels decreased from 3.20 ± 1.82 µIU/mL at baseline to 2.80 ± 1.51 by 24 months (p < 0.001), while free T4 levels increased from 13.50 ± 2.53 pmol/L to 14.20 ± 2.52 pmol/L (p = 0.020). Cognitive scores declined significantly, with MMSE scores dropping from 23.27 ± 4.64 to 21.80 ± 4.89 (p = 0.005) and MoCA scores from 21.20 ± 5.11 to 20.03 ± 5.51 (p = 0.012). Conclusion The results show a strong correlation between thyroid malfunction and cognitive loss in the elderly, emphasizing the need to closely monitor thyroid function to maintain cognitive function in this population.

Hyperthyroidism, hypothyroidism, thyroid stimulating hormone, and dementia risk: results from the NHANES 2011-2012 and Mendelian randomization analysis

Introduction

As the world ages, dementia places a heavy burden on society and the economy, but current methods of diagnosing dementia are still limited and there are no better therapies that target the causes of dementia. The purpose of this work is to explore the relationship between thyroid disease, thyroid stimulating hormone (TSH) concentrations, free tetraiodothyronine (FT4) concentrations and cognitive function.

Methods

This study utilized cognitive function and thyroid data from the 2011-2012 National Health and Nutrition Examination Survey (NHANES) to assess the relationship between different groups of TSH and FT4 concentrations and cognitive function using weighted logistic regression and restricted cubic spline (RCS), and then used two-sample Mendelian Randomization (MR) to assess the causal relationship between hyperthyroidism, hypothyroidism, TSH and FT4 concentrations with dementia.

Results

Our analysis of the 2011-2012 NHANES data showed that the individuals with low TSH concentrations had higher Alzheimer's Disease Word List Registry Consortium1 (CERAD1) and CERAD.delay.recall scores than individuals with high TSH concentrations, and individuals with low FT4 concentrations had higher CERAD3 and Animal Fluency Test scores than individuals with high FT4 concentrations. Our results also showed a non-linear relationship between serum TSH and FT4 concentrations and the Animal Fluency Test. The TSH concentrations within the range of 1.703 to 3.145 mIU/L exhibit a positive correlation with Animal Fluency Test, whereas concentrations outside this range are negatively correlated with Animal Fluency Test. The FT4 concentrations exhibited a positive correlation with Animal Fluency Test to the left of the FT4 concentrations inflection point (0.849 ng/L), whereas to the right of this inflection point, correlation was negative. MR analysis results further indicate that genetic predisposition to hyperthyroidism may be associated with a reduced risk of dementia and vascular dementia(VaD). Conversely, genetic predisposition to hypothyroidism appears to be linked with an increased risk of dementia and VaD. Additionally, genetic predisposition to elevated TSH concentrations may be correlated with a heightened risk of risk of Alzheimer's disease (AD).

Conclusion

This study provides evidence of a nonlinear relationship between TSH and FT4 concentrations and cognitive function, with hyperthyroidism decreasing the risk of dementia and VaD, hypothyroidism increasing the risk of dementia and VaD, and elevated serum TSH concentrations increasing the risk of AD. Furthermore, prioritizing early detection, diagnosis, and treatment through the assessment of thyroid function in individuals at high risk for developing dementia is of paramount importance. This strategy has the potential to significantly contribute to the prevention and deceleration of dementia progression.

Thyroid function variations within the reference range and cognitive function: A two-sample Mendelian randomization study

BACKGROUND

The causal relationship between thyroid function variations within the reference range and cognitive function remains unknown. We aimed to explore this causal relationship using a Mendelian randomization (MR) approach.

METHODS

Summary statistics of a thyroid function genome-wide association study (GWAS) were obtained from the ThyroidOmics consortium, including reference range thyroid stimulating hormone (TSH) (N = 54,288) and reference range free thyroxine (FT4) (N = 49,269). GWAS summary statistics on cognitive function were obtained from the Social Science Genetic Association Consortium (SSGAC) and the UK Biobank, including cognitive performance (N = 257,841), prospective memory (N = 152,605), reaction time (N = 459,523), and fluid intelligence (N = 149,051). The primary method used was inverse-variance weighted (IVW), supplemented with weighted median, Mr-Egger regression, and MR-Pleiotropy Residual Sum and Outlier. Several sensitivity analyses were conducted to identify heterogeneity and pleiotropy.

RESULTS

An increase in genetically associated TSH within the reference range was suggestively associated with a decline in cognitive performance (β = -0.019; 95%CI: -0.034 to -0.003; P = 0.017) and significantly associated with longer reaction time (β = 0.016; 95 % CI: 0.005 to 0.027; P = 0.004). Genetically associated FT4 levels within the reference range had a significant negative relationship with reaction time (β = -0.030; 95%CI:-0.044 to -0.015; P = 4.85 × 10-5). These findings remained robust in the sensitivity analyses.

CONCLUSIONS

Low thyroid function within the reference range may have a negative effect on cognitive function, but further research is needed to fully understand the nature of this relationship.

LIMITATIONS

This study only used GWAS data from individuals of European descent, so the findings may not apply to other ethnic groups.

Association between the oxidative balance score and thyroid function: Results from the NHANES 2007-2012 and Mendelian randomization study

BACKGROUND

Oxidative stress is a significant contributor to the development of various diseases, and the oxidative balance score (OBS) is a valuable tool for assessing the impact of dietary and lifestyle factors on oxidative stress in humans. Nevertheless, the precise relationship between OBS and thyroid function in adults remains elusive.

METHODS

This cross-sectional study comprised 6222 adult participants drawn from the National Health and Nutrition Examination Survey (NHANES) conducted from 2007 to 2012. Employing weighted multivariable linear regression modeling, the study estimated the connection between OBS quartiles and thyroid functions. The causal relationship between OBS components and thyroid function was analyzed by Mendelian randomization (MR).

RESULTS

We found a significant negative correlation between OBS and free thyroxine (FT4) and total thyroxine (TT4). Univariate and multivariate MR Analyses showed a causal relationship between BMI and FT4. Copper, smoking, and riboflavin showed a causal relationship with FT4 after moderation.

CONCLUSION

We found that a lifestyle high in antioxidant exposure reduced FT4 and TT4 levels in the population. We suggest that BMI, Copper, and Riboflavin are important factors in the regulation of FT4 levels.

Thyroid hormone biosynthesis and its role in brain development and maintenance

Thyroid hormones are critical modulators in the physiological processes necessary to virtually all tissues, with exceptionally fundamental roles in brain development and maintenance. These hormones regulate essential neurodevelopment events, including neuronal migration, synaptogenesis, and myelination. Additionally, thyroid hormones are crucial for maintaining brain homeostasis and cognitive function in adulthood. This chapter aims to offer a comprehensive understanding of thyroid hormone biosynthesis and its intricate role in brain physiology. Here, we described the mechanisms underlying the biosynthesis of thyroid hormones, their influence on various aspects of brain development and ongoing maintenance, and the proteins in the brain that are responsive to these hormones. This chapter was geared towards broadening our understanding of thyroid hormone action in the brain, shedding light on potential therapeutic targets for neurodevelopmental and neurodegenerative disorders.

Impaired Sensitivity to Thyroid Hormones is Associated with Mild Cognitive Impairment in Euthyroid Patients with Type 2 Diabetes

Purpose

The prevalence of mild cognitive impairment (MCI) in patients with type 2 diabetes (T2D) is rapidly increasing. Thyroid hormones are key regulators of cognitive function in adults. The purpose of this study was to investigate the relationship between thyroid hormone sensitivity and MCI in euthyroid T2D patients.

Patients and Methods

A total of 400 euthyroid T2D patients were enrolled in this cross-sectional study, including 218 patients with normal cognition and 182 MCI patients. The Montreal Cognitive Assessment (MoCA) was used to evaluate cognitive function. The free triiodothyronine to free thyroxine (FT3/FT4) ratio was calculated as a measure of peripheral sensitivity to thyroid hormones; the thyroid-stimulating hormone index (TSHI), thyrotrophic thyroxine resistance index (TT4RI) and thyroid feedback quantile-based index (TFQI) were calculated as measures of central sensitivity to thyroid hormones. Linear regression analysis and logistic regression analysis were performed to explore the relationships between these indices of thyroid hormone sensitivity and the MoCA score and MCI, respectively.

Results

Compared with the normal cognitive function group, patients in the MCI group had higher TSHI, TT4RI and TFQI but a lower FT3/FT4 ratio (P<0.05). The MoCA score was positively correlated with the FT3/FT4 ratio but negatively correlated with TSHI, TT4RI and TFQI (P< 0.05). Multivariate logistic regression analysis showed that a low FT3/FT4 ratio and high TSHI, TT4RI and TFQI were independently associated with MCI (P<0.05). After adjustment for confounding factors, the odds ratio (OR) for the association between MCI and the highest tertile of the FT3/FT4 was 0.455 (95% CI: 0.264-0.785), for the highest tertile of TSHI, the OR was 2.380 (95% CI: 1.376-4.119), for the highest tertile of TT4RI, the OR was 2.342 (95% CI:1.353-4.054), and for the highest tertile of TFQI, the OR was 2.536 (95% CI: 1.466-4.387) (P< 0.05).

Conclusion

Impaired sensitivity to thyroid hormones is associated with MCI in euthyroid T2D patients.

Executive function performance in middle-aged adults

Executive functions have been widely studied in the extreme of ages, but studies in middle-aged adults remain largely neglected. Education and gender are known to influence cognitive performance; however, their effect on executive function in middle-aged adults remains unclear.

Objective

The study aimed to observe the effect of hierarchy of educational qualifications (graduate, postgraduate, and PhD) and gender on various executive function tests across middle-aged adults with or without comorbidity.

Methods

A total of 66 middle-aged individuals volunteered for the study (mean age=48.45±5.45 years; 20 graduates, 28 postgraduates, and 18 PhD; 36 males and 30 females; 38 healthy adults and 28 adults with comorbidities). Each subject performed a test assessing short-term memory, spatial working memory, and multitasking abilities on the Cambridge Neuropsychological Test Automated Battery with rest periods in no specific order of tests. Key parameters of cognitive tests were analyzed for differences in educational qualifications (ANOVA), gender (t-test), and the effect of comorbidity as a covariate (ANCOVA).

Results

PhDs performed significantly better (p<0.05) in multitasking than graduates and had superior visuospatial working memory (fewer errors). Differences in simultaneous matching abilities, lower incongruence cost and multitasking cost were statistically significant in healthy females than in males.

Conclusion

On considering adults with comorbidity, those with higher educational attainment retained the ability to multitask compared to their healthy counterparts, which was not seen in the group with lower educational attainment. Thus, higher educational attainment attenuated the influence of comorbidities and deterioration of executive functions in general in middle-aged adults.

Association of vascular and degenerative brain pathologies and past medical history from the National Alzheimer's Coordinating Center Database

The relationship between past medical histories (PMH) and dementia-related neuropathologies is not well understood. Using the National Alzheimer's Coordinating Center (NACC) database, we explored the relationship between patient-reported PMH and various vascular and degenerative neuropathologies. We examined the following PMH: transient ischemic attack (TIA), stroke, traumatic brain injury, seizures, hypertension, cardiovascular events, hypercholesterolemia, B12 deficiency, diabetes mellitus, and thyroid disease. We dichotomized the following neuropathologies: atherosclerosis, arteriolosclerosis, cerebral amyloid angiopathy (CAA), Alzheimer disease neuropathology (ADNP), Lewy bodies (LB), hippocampal sclerosis, frontotemporal lobar degeneration (FTLD), and TAR DNA-binding protein-43 (TDP-43). Separate logistic regression models assessed the relationship between the outcome of individual neuropathologies and all PMHs. Additional logistic regressions were stratified by sex to further examine these associations. Hypertension history was associated with an increased likelihood of atherosclerosis (OR = 1.7) and arteriolosclerosis (OR = 1.3), but decreased odds of ADNP (OR = 0.81), CAA (OR = 0.79), and LB (OR = 0.78). History of TIA was associated with an increased likelihood of atherosclerosis (OR = 1.3) and arteriolosclerosis (OR = 1.4) and lower odds of ADNP (OR = 0.72). Seizure history was associated with an increased likelihood of ADNP (OR = 1.9) and lower odds of FTLD (OR = 0.49). Hypertension history was associated with a greater likelihood of vascular pathologies yet a lower likelihood of ADNP and other neurodegenerative pathologies.

Neuropsychiatric Manifestations of Thyroid Diseases

Thyroid disorders are known to cause neuropsychiatric manifestations. Various neuropsychiatric manifestations are depression, dementia, mania, and autoimmune Hashimoto encephalopathy. Numerous investigations carried out in the previous 50-60 years have been evaluated critically. The pathophysiology of neuropsychiatric symptoms of thyroid diseases is described in the current study and its link with autoimmune Hashimoto encephalopathy is also discussed. Furthermore, this paper also describes the association between thyroid-stimulating hormones and cognitive impairment. Hypothyroidism is associated with depression and mania, and hyperthyroidism is linked with dementia and mania. The association between Graves' disease and various mental disorders such as depressive and anxiety disorders is also discussed. The aim of this study is to review the relationship between various neuropsychiatric disorders and thyroid diseases. A literature search from the PubMed database to find various neuropsychiatric manifestations of thyroid disorders in the adult population was conducted. According to the review of the studies, cognitive impairment can result from thyroid disease. It has not been possible to demonstrate how hyperthyroidism can hasten the process of developing dementia. However, subclinical hyperthyroidism, thyroid-stimulating hormone (TSH) levels below the normal range, and high free thyroxine (T4) levels all raise the risk of dementia in the elderly. Additionally, the potential mechanisms underlying this association have been examined. A quick summary of the research on mania as a clinical symptom of hypothyroidism and its likely causes and pathogenesis is also reviewed. There is no dearth of evidence that describes various neuropsychiatric manifestation in thyroid disorders.

Association of Subclinical Thyroid Dysfunction with Cognitive Impairment in Rats: The Role of Autophagy

BACKGROUND

We investigated the effect of subclinical hyperthyroidism and subclinical hypothyroidism on cognitive function in rats and the role of autophagy in this process.

METHODS

Forty Wistar rats were randomized into normal control (NC), hyperthyroidism (Hyper), hypothyroidism (Hypo), subclinical hyperthyroidism (sHyper), and subclinical hypothyroidism (sHypo) groups. Cognitive function (spatial learning and memory) was tested by the Morris water maze test. Hippocampal histopathology was analyzed by H&E staining, and expression levels of caspase-3 in hippocampal CA1 neurons were measured. In addition, immunoblot analysis was performed to detect hippocampal autophagy-related proteins.

RESULTS

Escape latency from day 1 to day 4 was significantly longer in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). In addition, the number of rats crossing the virtual platform was significantly lower in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). Compared with the NC group, all four groups had significantly lower residence time in the target quadrant (P < 0.05). Beclin-1 and LC3-II protein expression in hippocampal tissues was significantly higher in the Hyper and sHyper groups than in the NC group (P < 0.01). Beclin-1 and LC3-II protein expression in hippocampal tissues did not significantly differ between the sHypo group and NC group (P > 0.05).

CONCLUSIONS

Subclinical thyroid dysfunction in rats might lead to cognitive impairment. Subclinical hyperthyroidism might be associated with excessive activation of autophagy and hippocampal neuron damage and necrosis.

Association of Hypothyroidism and the Risk of Cognitive Dysfunction: A Meta-Analysis

Objectives: The purpose of this meta-analysis was to assess whether there is an association between hypothyroidism and the risk of cognitive dysfunction. Methods: PubMed, Cochrane Library, and Embase were searched for relevant studies published from database inception to 4 May 2022, using medical subject headings (MeSHs) and keywords. Results: Eight studies involving 1,092,025 individuals were included, published between 2010 and 2021. The pooled analysis showed that there was no association between hypothyroidism and cognitive dysfunction (OR = 1.13, 95% CI = 0.84−1.51, p = 0.426), including both all-cause dementia (OR = 1.04, 95% CI = 0.76−1.43, p = 0.809) and cognitive impairment (OR = 1.50, 95% CI = 0.68−3.35, p = 0.318). Neither overt hypothyroidism (OR = 1.19, 95% CI = 0.70−2.02, p = 0.525) nor subclinical hypothyroidism (OR = 1.04, 95% CI = 0.73−1.48, p = 0.833) was associated with cognitive dysfunction. Neither prospective cohort (OR = 1.08, 95% CI = 0.77−1.51, p = 0.673) nor cross-sectional studies (OR = 1.23, 95% CI = 0.63−2.42, p = 0.545) had any effect on the association. Interestingly, the risk of cognitive dysfunction was significantly increased in the group not adjusted for vascular comorbidity (OR = 1.47, 95% CI = 1.07−2.01, p = 0.017), while it was reduced in the adjusted group (OR =0.82, 95% CI = 0.79−0.85, p < 0.001). Conclusions: This meta-analysis shows that hypothyroidism was associated with a reduced risk of cognitive dysfunction after adjustment for vascular-disease comorbidities. More prospective observational studies are needed in the future to investigate the relationship between hypothyroidism and cognitive dysfunction.

Association of serum thyroid hormone levels with positron emission tomography imaging in non-demented older adults

BACKGROUND

Although increasing evidence indicates that even variations in normal range thyroid function are associated with Alzheimer's disease (AD), the association between serum thyroid hormone levels within the reference range and AD biomarkers remains unclear. This study examined whether variations in thyroid hormones within the reference range are associated with brain amyloid burden and cortical glucose metabolism in older adults without dementia.

METHODS

One hundred and two non-demented older adults underwent ¹¹ C-Pittsburgh Compound B positron emission tomography (PiB-PET), ¹⁸ F-fluorodeoxyglucose (FDG)-PET, and measurement of serum thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) levels. The discrimination between PiB-negative and PiB-positive subgroup was made on the basis of a subject's cortical uptake value ratio greater than 1.4. The association of serum thyroid hormone levels with global PiB or FDG uptake, and PiB or FDG uptake in each region of interest, including frontal and temporoparietal lobes and posterior cingulate gyrus, was analysed using a multiple regression model with adjustment for covariates, including age, gender, years of education, apolipoprotein E4 status or PiB uptake value.

RESULTS

In the PiB-positive subgroup, the serum TSH levels positively associated with the global FDG uptake (β = 0.471, P = 0.003) and FDG uptake in the frontal and temporoparietal lobes (β = 0.466, P = 0.003, β = 0.394, P = 0.012, respectively); the serum-free T3 levels negatively associated with the FDG uptake in the temporoparietal lobe and posterior cingulate region (β = -0.351, P = 0.033, β = -0.544, P = 0.002, respectively). The PiB-negative subgroup showed no significant associations. The serum thyroid hormone levels did not correlate with the global PiB uptake and PiB uptake in each region.

CONCLUSIONS

The variations in the thyroid hormones within the reference ranges are associated with glucose metabolism, particularly in the specific regions affected by the neuropathologic changes of AD, in non-demented older adults with brain amyloid burden.

TREM2 is thyroid hormone regulated making the TREM2 pathway druggable with ligands for thyroid hormone receptor

Triggering receptor expressed on myeloid cells-2 (TREM2) is a cell surface receptor on macrophages and microglia that senses and responds to disease-associated signals to regulate the phenotype of these innate immune cells. The TREM2 signaling pathway has been implicated in a variety of diseases ranging from neurodegeneration in the central nervous system to metabolic disease in the periphery. Here, we report that TREM2 is a thyroid hormone-regulated gene and its expression in macrophages and microglia is stimulated by thyroid hormone and synthetic thyroid hormone agonists (thyromimetics). Our findings report the endocrine regulation of TREM2 by thyroid hormone, and provide a unique opportunity to drug the TREM2 signaling pathway with orally active small-molecule therapeutic agents.

Free thyroxine, brain frailty and clock drawing test performance in patients with acute minor stroke or transient ischaemic attack

OBJECTIVE

Thyroid dysfunction is associated with an elevated risk of cognitive decline, but the mechanism underlying this relationship is elusive. In this study, we investigate the relationships between free thyroxine (FT4), brain frailty and clock drawing test (CDT) performance in patients with acute minor stroke or transient ischaemic attack (TIA).

DESIGN, PATIENTS AND MEASUREMENTS

A total of 204 consecutive patients admitted to our hospital within 72 h after the onset of acute minor stroke or TIA were prospectively enroled and categorized in terms of quartiles of FT4 between March 2018 and August 2019. Brain frailty on magnetic resonance imaging was rated according to previously published criteria. Cognitive performance was assessed with the CDT.

RESULTS

Generalized linear analysis revealed that FT4 was independently associated with higher brain frailty score after adjusting potential confounders (β, 0.03; 95% confidence interval [CI], 0.00-0.06; p = 0.0205), which is consistent with the result of FT4 (quartile) as a categorical variable (β, 0.34; 95% CI, 0.01-0.68; p = 0.0059; p_trend  = 0.0807). A nonlinear relationship was detected between FT4 and brain frailty score, which had an inflection point of 1.19. FT4 was also associated with poor CDT performance (odds ratio, 1.15; 95% CI, 1.04-1.26; p = 0.0051). And mediation analysis found that brain frailty partially mediated the positive relationship between FT4 and poor CDT performance (indirect effect = 0.0024; 95% CI, 0.0003-0.01, p = 0.04).

CONCLUSIONS

Our findings suggested that a higher FT4 level was associated with a higher brain frailty score and poorer CDT performance, and brain frailty might play an important effect on the association between FT4 and cognitive decline.

Association of Thyroid Dysfunction With Cognitive Function: An Individual Participant Data Analysis

IMPORTANCE

In clinical guidelines, overt and subclinical thyroid dysfunction are mentioned as causal and treatable factors for cognitive decline. However, the scientific literature on these associations shows inconsistent findings.

OBJECTIVE

To assess cross-sectional and longitudinal associations of baseline thyroid dysfunction with cognitive function and dementia.

DESIGN, SETTING, AND PARTICIPANTS

This multicohort individual participant data analysis assessed 114 267 person-years (median, 1.7-11.3 years) of follow-up for cognitive function and 525 222 person-years (median, 3.8-15.3 years) for dementia between 1989 and 2017. Analyses on cognitive function included 21 cohorts comprising 38 144 participants. Analyses on dementia included eight cohorts with a total of 2033 cases with dementia and 44 573 controls. Data analysis was performed from December 2016 to January 2021.

EXPOSURES

Thyroid function was classified as overt hyperthyroidism, subclinical hyperthyroidism, euthyroidism, subclinical hypothyroidism, and overt hypothyroidism based on uniform thyrotropin cutoff values and study-specific free thyroxine values.

MAIN OUTCOMES AND MEASURES

The primary outcome was global cognitive function, mostly measured using the Mini-Mental State Examination. Executive function, memory, and dementia were secondary outcomes. Analyses were first performed at study level using multivariable linear regression and multivariable Cox regression, respectively. The studies were combined with restricted maximum likelihood meta-analysis. To overcome the use of different scales, results were transformed to standardized mean differences. For incident dementia, hazard ratios were calculated.

RESULTS

Among 74 565 total participants, 66 567 (89.3%) participants had normal thyroid function, 577 (0.8%) had overt hyperthyroidism, 2557 (3.4%) had subclinical hyperthyroidism, 4167 (5.6%) had subclinical hypothyroidism, and 697 (0.9%) had overt hypothyroidism. The study-specific median age at baseline varied from 57 to 93 years; 42 847 (57.5%) participants were women. Thyroid dysfunction was not associated with global cognitive function; the largest differences were observed between overt hypothyroidism and euthyroidism-cross-sectionally (-0.06 standardized mean difference in score; 95% CI, -0.20 to 0.08; P = .40) and longitudinally (0.11 standardized mean difference higher decline per year; 95% CI, -0.01 to 0.23; P = .09). No consistent associations were observed between thyroid dysfunction and executive function, memory, or risk of dementia.

CONCLUSIONS AND RELEVANCE

In this individual participant data analysis of more than 74 000 adults, subclinical hypothyroidism and hyperthyroidism were not associated with cognitive function, cognitive decline, or incident dementia. No rigorous conclusions can be drawn regarding the role of overt thyroid dysfunction in risk of dementia. These findings do not support the practice of screening for subclinical thyroid dysfunction in the context of cognitive decline in older adults as recommended in current guidelines.

Predictive Value of Gut Microbiome for Cognitive Impairment in Patients with Hypertension

A connection exists between hypertension (HTN) and cognitive impairment (CI) or gut microbiota (GM) and neuropsychiatric disease. However, the link between GM and HTNCI has not been illustrated. This study endeavoured to profile the landscape of GM in HTNCI patients and evaluate the value of GM as HTNCI biomarkers. We recruited 128 patients with hypertension and assigned them to two groups of different MoCA scores. Clinical and biological data were recorded. GM composition was illustrated with 16S ribosomal RNA sequencing, and the dominant species were identified by linear discriminant analysis Effect Size (LEfSe). It showed higher abundance of TM7 and lower abundances of Veillonella and Peptoniphilus in the HTNCI group than in the HTN without cognitive impairment (HTNnCI) group. We next clarified the link between GM and MoCA scores or HTNCI factors. KEGG analysis revealed the involvement of decreased bile secretion. An evident correlation showed up between HTNCI and Veillonella abundance (P = 0.0340). We concluded that some representative GM species, especially Veillonella, could predict cognitive impairment in hypertension patients, making them potential benchmarks of HTNCI.

Does Hormone Supplementation With Levothyroxine Improve Hypothyroid Impaired Cognitive Dysfunction?

Hypothyroidism is a widespread condition in the United States, affecting approximately 5% of the adult population. Although the clinical use of levothyroxine is well understood, its effect on preventing dementia is not well established. While the exact role of thyroid hormones in the adult brain is unknown, it is apparent that poor thyroid function can lead to mood swings, cognitive impairment, and other psychiatric symptoms. Most studies demonstrate an association between thyroid health and cognition, specifically slow processing of information, decreased effectiveness of executive functions, and lack of learning. This study aims to review the effect of levothyroxine on dementia. We searched electronic databases such as PubMed, Google Scholar, Science Direct, Cochrane, gray literature, and the references of included articles to find relevant articles. Two investigators independently identified eligible studies, screened title/abstract, and extracted data. We identified a total of 319 citations through a database search with six studies (case-control, longitudinal, cross-sectional, randomized controlled trials) meeting the inclusion criteria. Studies with moderate to low risk of bias were evaluated using their respective quality check tools. Five of six studies showed a positive impact of levothyroxine (LT-4) on dementia. According to these studies, the plausible rationale behind the reversal of memory with LT-4 treatment is restoring thyroid-stimulating hormone (TSH), thyroxine (T4) levels, and gamma-aminobutyric acid (GABA) concentrations. People with abnormal thyroid function should be screened for cognitive dysfunction using specific neurocognitive tests and start treatment with LT-4 regardless of symptom presentation. Multi-dose randomized placebo-controlled intervention studies are recommended to assess the effect of LT-4 on lowering the risk of dementia in hypothyroid patients.

The poorly conducted orchestra of steroid hormones, oxidative stress and inflammation in frailty needs a maestro: Regular physical exercise

This review outlines the various factors associated with unhealthy aging which includes becoming frail and dependent. With many people not engaging in recommended exercise, facilitators and barriers to engage with exercise must be investigated to promote exercise uptake and adherence over the lifespan for different demographics, including the old, less affluent, women, and those with different cultural-ethnic backgrounds. Governmental and locally funded public health messages and environmental facilitation (gyms, parks etc.) can play an important role. Studies have shown that exercise can act as a conductor to balance oxidative stress, immune and endocrine functions together to promote healthy aging and reduce the risk for age-related morbidities, such as cardiovascular disease and atherosclerosis, and promote cognition and mood over the lifespan. Like a classic symphony orchestra, consisting of four groups of related musical instruments - the woodwinds, brass, percussion, and strings - the aging process should also perform in harmony, with compassion, avoiding the aggrandizement of any of its individual parts during the presentation. This review discusses the wide variety of molecular, cellular and endocrine mechanisms (focusing on the steroid balance) underlying this process and their interrelationships.

The Role of Thyroid Function in Alzheimer's Disease

The thyroid gland is crucial for the regulation of metabolism, growth, and development of various tissues, organs, systems, including the central nervous system. Recent studies have implicated the role of thyroid dysfunction in the etiology of Alzheimer's disease (AD), while AD leads to a significant increase in the prevalence of thyroid dysfunction. In this review, we have analyzed the role of thyroid function in the pathophysiology of AD as well as its biomarkers. The present review aims to provide encouraging targets for early screening of AD risk factors and intervention strategies.

Subtle Thyroid Dysfunction Is Not Associated with Cognitive Decline: Results from the ELSA-Brasil

BACKGROUND

Subtle thyroid alterations have a controversial role in cognition.

OBJECTIVE

We investigated the longitudinal association of baseline thyroid function, thyrotropin (TSH), and thyroxine (FT4) levels with cognitive performance after 4 years of follow-up in middle-aged and older adults without overt thyroid dysfunction.

METHODS

We included 4,473 individuals, age≥55 years at the second study wave, without overt thyroid dysfunction at baseline. Individuals were divided according to thyroid function and TSH and FT4 tertiles. Cognition was assessed at baseline and after 4 years of follow-up by the word recall (DWR), semantic verbal fluency (SVF), and trail making (TMT) tests. The longitudinal association of thyroid function and TSH and FT4 tertiles with cognitive performance was investigated using generalized estimating equations adjusted for sociodemographic characteristics, lifestyle, cardiovascular risk factors and depression.

RESULTS

There was no longitudinal association of thyroid function and TSH and FT4 baseline levels with performance on the cognitive tests. However, there was a baseline cross-sectional U-shaped association of FT4 tertiles with poorer performance in the SVF (first FT4 tertile: β= -0.11, 95% CI = -0.17; -0.04; third FT4 tertile: β= -0.10, 95% CI = -0.17; -0.04) and of the third FT4 tertile with poorer performance in the DWR (β= -0.09, 95% CI = -0.16; -0.02).

CONCLUSION

Thyroid function and hormone levels were not associated with cognitive decline during 4 years of follow-up in middle-aged and older adults without overt thyroid dysfunction. Future studies with longer follow-up could clarify the implications of subtle thyroid alterations in cognition.

The Impact of the COVID-19 Pandemic on the Cognition of People with Dementia

(1) Background: To limit the COVID-19 outbreak, the Italian government implemented social restrictions that may have had psychological and cognitive repercussions on people with dementia. We aimed to analyze cognitive decline during the pandemic year in people evaluated in a memory clinic in northern Italy, the epicenter of COVID-19 spread. (2) Methods: A single-center retrospective study was carried out, including individuals with annual follow-up evaluated in three different years (2020-GROUP, 2019-GROUP, 2018-GROUP). We performed an intergroup comparison of cognitive decline over a one-year follow-up, and an intragroup comparison in the 2020-GROUP to analyze the five-year cognitive decline trajectory, as measured by the MMSE. (3) Results: The 2020-GROUP showed a significant loss of MMSE points per year in the considered follow-up period compared with the 2019-GROUP and 2018-GROUP (p = 0.021). Demographics, clinical features, and the other analyzed variables, including rate of diagnosis, therapy, and comorbidities, did not significantly differ between groups. The five-year cognitive decline trajectory confirmed a significant worsening of cognitive decline between 2019 and 2020 (p < 0.001), while the decrease in MMSE scores was not statistically significant between previous time points. (4) Conclusions: COVID-19 pandemic measures have induced a significant worsening of cognitive decline in people with dementia, needing more careful assistance to minimize the adverse effects of social isolation in case of future lockdowns.

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

The relation between thyroid dysregulation and impaired cognition/behaviour: An integrative review

Despite decades of research on the relation between thyroid diseases and cognition, the nature of this relationship remains elusive. An increasing prevalence of cognitive impairment and thyroid dysfunction has been consistently observed with ageing. Also, there appears to be an association between thyroid disorders and cognitive decline. Given the increasing global burden of dementia, elucidating the relationship between thyroid disorders as a potentially modifiable risk factor of cognitive impairment was the main goal of this review. We summarise the current literature examining the relationship between thyroid hormonal dysregulation and cognition or behaviour. We present the available imaging and pathological findings related to structural and functional brain changes related to thyroid hormonal dysregulation. We also propose potential mechanisms of interaction between thyroid hormones, autoantibodies and cognition/behaviour. Effects of gender, ethnicity and environmental factors are also briefly discussed. This review highlights the need for long-term prospective studies to capture the course of brain functional changes associated with the incidence and progression of thyroid dysregulations along with the confounding effects of non-modifiable risk factors such as gender and ethnicity. Moreover, double-blind controlled clinical trials are necessary to devise appropriate treatment plans to prevent cognitive consequences of over or undertreatment of thyroid disorders.

TREM2 is thyroid hormone regulated making the TREM2 pathway druggable with ligands for thyroid hormone receptor

Triggering receptor expressed on myeloid cells-2 (TREM2) is a cell surface receptor on macrophages and microglia that senses and responds to disease associated signals to regulate the phenotype of these innate immune cells. The TREM2 signaling pathway has been implicated in a variety of diseases ranging from neurodegeneration in the central nervous system to metabolic disease in the periphery. We report here that TREM2 is a thyroid hormone regulated gene and its expression in macrophages and microglia is stimulated by thyroid hormone. Both endogenous thyroid hormone and sobetirome, a synthetic thyroid hormone agonist drug, suppress pro-inflammatory cytokine production from myeloid cells including macrophages that have been treated with the SARS-CoV-2 spike protein which produces a strong, pro-inflammatory phenotype. Thyroid hormone agonism was also found to induce phagocytic behavior in microglia, a phenotype consistent with activation of the TREM2 pathway. The thyroid hormone antagonist NH-3 blocks the anti-inflammatory effects of thyroid hormone agonists and suppresses microglia phagocytosis. Finally, in a murine experimental autoimmune encephalomyelitis (EAE) multiple sclerosis model, treatment with Sob-AM2, a CNS-penetrating sobetirome prodrug, results in increased Trem2 expression in disease lesion resident myeloid cells which correlates with therapeutic benefit in the EAE clinical score and reduced damage to myelin. Our findings represent the first report of endocrine regulation of TREM2 and provide a unique opportunity to drug the TREM2 signaling pathway with orally active small molecule therapeutic agents.

Changes of Structural and Functional Attention Control Networks in Subclinical Hypothyroidism

Objective: This study aimed to explore the structural changes in patients with subclinical hypothyroidism (SCH) using voxel-based morphometry (VBM) and to investigate the altered attentional control networks using functional MRI (fMRI) during the performance of a modified Stroop task with Chinese characters. Methods: High-resolution three-dimensional (3D) T1-weighted images and an fMRI scan were taken from 18 patients with SCH and 18 matched control subjects. The Montreal Cognitive Assessment Chinese-revised (MoCA-CR) and the Stroop task were used to evaluate the cognitive and attention control of the participants. Results: Compared to controls, the VBM results showed decreased gray matter volumes (GMVs) in bilateral prefrontal cortices (PFCs, including middle, medial, and inferior frontal gyri), cingulate gyrus, precuneus, left middle temporal gyrus, and insula in patients with SCH. The fMRI results showed a distributed network of brain regions in both groups, consisting of PFCs (including superior and middle and inferior frontal cortices), anterior cingulate cortex (ACC), posterior cingulate cortex, and precuneus, as well as the insula and caudate nucleus. Compared to controls, the SCH group had lower activation of the above brain areas, especially during the color-naming task. In addition, the normalized GMV (nGMV) was negatively correlated with thyroid-stimulating hormone (TSH) level (r = -0.722, p < 0.001). Conclusion: Results indicate that patients with SCH exhibit reduced GMVs, altered BOLD signals, and activation in regions associated with attention control, which further suggest that patients with SCH may have attentional control deficiency, and the weakened PFC-ACC-precuneus brain network might be one of the neural mechanisms. Negative correlations between nGMV and TSH suggest that TSH elevation may induce abnormalities in the cortex.

Cognitive Impairment and Associated Factors Among Adult Hypothyroid Patients in Referral Hospitals, Amhara Region, Ethiopia: Multicenter Cross-Sectional Study

BACKGROUND

Cognitive impairment is a common complication of hypothyroidism that affects the patient's quality of life in different aspects. In Ethiopia, though the prevalence of hypothyroidism is high the magnitude of cognitive impairment among these patients is not known. Therefore, the current study is aimed at determining the prevalence of cognitive impairment and associated factors among adult hypothyroid patients.

METHODS

An institution-based cross-sectional study was employed from February 24 to May 22, 2020, to assess the prevalence of cognitive impairment and associated factors among adult hypothyroid patients. Data was collected by a pretested interviewer-administered structured questionnaire and standardized Mini-mental state examination (SMMSE) tool. A cluster sampling technique was used. Data was entered into Epidata version 4.6 and exported into a statistical package for social science (SPSS) version 25 for further analysis. Both bivariable and multivariable logistic regression analyses were done. A 95% confidence interval and P-value <0.05 were used to declare statistical significance.

RESULTS

A total of 216 adult hypothyroid patients were included with a response rate of 98.6%. The mean age was 42.5 (± 11) years. The prevalence of cognitive impairment was 27.3% (95% CI (21.7, 33.8)) and it was significantly associated with increased age (AOR = 1.23, 95% CI (1.11, 1.34)), increased duration of illness (AOR = 1.48, 95% CI (1.14, 1.90)) and high thyroid-stimulating hormone (TSH) level (AOR = 1.3, 95% CI (1.1, 1.6)).

CONCLUSION

The prevalence of cognitive impairment among hypothyroid patients was high. Increased age, increased duration of illness and high TSH levels were significantly associated with cognitive impairment. Hence, early screening of cognitive impairment among hypothyroid patients with increased age, increased duration of illness and high TSH level should be given due emphasis to increase patients quality of life.

Thyroid hormones in diabetes, cancer, and aging

Thyroid function is central in the control of physiological and pathophysiological processes. Studies in animal models and human research have determined that thyroid hormones modulate cellular processes relevant for aging and for the majority of age‐related diseases. While several studies have associated mild reductions on thyroid hormone function with exceptional longevity in animals and humans, alterations in thyroid hormones are serious medical conditions associated with unhealthy aging and premature death. Moreover, both hyperthyroidism and hypothyroidism have been associated with the development of certain types of diabetes and cancers, indicating a great complexity of the molecular mechanisms controlled by thyroid hormones. In this review, we describe the latest findings in thyroid hormone research in the field of aging, diabetes, and cancer, with a special focus on hepatocellular carcinomas. While aging studies indicate that the direct modulation of thyroid hormones is not a viable strategy to promote healthy aging or longevity and the development of thyromimetics is challenging due to inefficacy and potential toxicity, we argue that interventions based on the use of modulators of thyroid hormone function might provide therapeutic benefit in certain types of diabetes and cancers.

Blood-based biomarkers in hypothalamic-pituitary axes for the risk of dementia or cognitive decline: a systematic review and meta-analysis

Blood-based biomarkers are ideal candidates for dementia prediction. This systematic review and meta-analysis aimed to evaluate longitudinal relationships of blood hormones and hormone-binding proteins in hypothalamic-pituitary (HP) axes with dementia or cognitive decline. PubMed, MEDLINE, EMBASE, PsycINFO, and BIOSIS were systematically searched from 1919 to June 2020. Fifteen types of hormones and four types of hormone-binding proteins were measured in 48 prospective studies. Increased risk of dementia or cognitive decline could be predicted by elevated blood concentrations of free-thyroxine (free-T4, RR = 1.06, p = 0.001) and sex hormone-binding globulin (SHBG, RR = 1.10, p = 0.025). Lower thyroid-stimulating hormone (TSH) levels within (RR = 1.28, p < 0.001) and below (RR = 1.27, p = 0.004) the normal range were both risky. Current evidence suggests the alterations of multiple blood molecules in HP axes, especially TSH, free-T4, and SHBG precede the incidence of dementia or cognitive decline. The underpinning etiology remains to be elucidated in the future.

Is Hyperthyroidism a Possible Etiology of Early Onset Dementia?

Dementia, a disabling syndrome of the elderly characterized by the decline in memory and cognition, is increasing in incidence and affects not only the individual but also their family and close ones. Hyperthyroidism can mimic many other diseases and untreated hyperthyroidism can lead to adverse problems of various systems including the heart, bones, muscles, menstrual cycle, and fertility. In this article, we have tried to evaluate the association between hyperthyroidism and dementia, as well as the impact of hyperthyroidism management in the treatment and prevention of dementia. Studies available in the PubMed database have been used, excluding animal studies and including studies of adults above the age of 50. The analysis of studies reveals that thyroid dysfunction can lead to cognitive impairment. It has not been able to prove that hyperthyroidism can lead to an earlier onset of dementia. But subclinical hyperthyroidism, thyroid-stimulating hormone (TSH) levels below the normal range, and high free thyroxine (T4) levels increase the risk of dementia among the elderly. The possible mechanisms involved in this association have also been discussed. Thus, we concluded that it is essential to detect and manage hyperthyroidism at an earlier stage since hyperthyroidism increases the risk of dementia. The possibility of using antithyroid treatment in euthyroid dementia is yet to be studied extensively.

The effect of jet lag on the human brain: A neuroimaging study

Jet lag is commonly experienced when travelers cross multiple time zones, leaving the wake-sleep cycle and intrinsic biological "clocks" out of synchrony with the current environment. The effect of jet lag on intrinsic cortical function remains unclear. Twenty-two healthy individuals experiencing west-to-east jet lag flight were recruited. Brain structural and functional magnetic resonance studies, as well as psychological and neurohormonal tests, were carried out when participants returned from travel over six time zones and 50 days later when their jet lag symptoms had resolved. During jet lag, the functional brain network exhibited a small-world topology that was shifted toward regularity. Alterations during jet lag relative to recovery included decreased basal ganglia-thalamocortical network connections and increased functional connectivity between the medial temporal lobe subsystem and medial visual cortex. The lower melatonin and higher thyroid hormone levels during jet lag showed the same trend as brain activity in the right lingual gyrus. Although there was no significant difference between cortisol measurements during and after jet lag, cortisol levels were associated with temporal lobe activity in the jet lag condition. Brain and neuroendocrine changes during jet lag were related to jet lag symptoms. Further prospective studies are needed to explore the time course over which jet lag acts on the human brain.

Altered attention networks in patients with thyroid dysfunction: A neuropsychological study

Patients with thyroid dysfunction (31 hypothyroid, 32 subclinical hypothyroidism, 34 hyperthyroid, and 30 subclinical hyperthyroidism) and 37 euthyroid control subjects were recruited and performed the attention network test (ANT), which can simultaneously examine the alertness, orientation and execution control of the participants. Patients with hypothyroidism had abnormalities in the alerting network, and those with hyperthyroidism had impairments of the alerting and executive control networks. No attention networks deficit existed in patients with subclinical hyperthyroidism and subclinical hypothyroidism. The anxiety and depression scores of patients with thyroid dysfunction were significantly higher than those of the healthy control group. Covariance analysis demonstrated that interactions between group and Hamilton Anxiety Scale scores, group and HAMD score were not significant, but there was a significant main effect for group when analyzing the difference in values of the alerting network between groups. Further, the efficiency of the executive control network was negatively correlated with the T4 level in the hypothyroidism group, and positively correlated with the T4 level in the hyperthyroidism group. T4 or T3 level and efficiencies of the executive control network had a significant quadratic U-shaped relationship in all participants. In summary, the patients with four kinds of thyroid dysfunction exhibited different characteristics of ANT performance. Patients with thyroid dysfunction had various degrees of anxiety and depression disorders, but anxiety and depression disorders had no effect on the differences in the executive control network between the groups.

Exogenous 3-Iodothyronamine Rescues the Entorhinal Cortex from β-Amyloid Toxicity

Background: A novel form of thyroid hormone (TH) signaling is represented by 3-iodothyronamine (T₁AM), an endogenous TH derivative that interacts with specific molecular targets, including trace amine-associated receptor 1 (TAAR₁), and induces pro-learning and anti-amnestic effects in mice. Dysregulation of TH signaling has long been hypothesized to play a role in Alzheimer's disease (AD). In the present investigation, we explored the neuroprotective role of T₁AM in beta amyloid (Aβ)-induced synaptic and behavioral impairment, focusing on the entorhinal cortex (EC), an area that is affected early by AD pathology. Methods: Field potentials were evoked in EC layer II, and long-term potentiation (LTP) was elicited by high frequency stimulation (HFS). T₁AM (5 μM) and/or Aβ(1-42) (200 nM), were administered for 10 minutes, starting 5 minutes before HFS. Selective TAAR₁ agonist RO5166017 (250 nM) and TAAR₁ antagonist EPPTB (5 nM) were also used. The electrophysiological experiments were repeated in EC-slices taken from a mouse model of AD (mutant human amyloid precursor protein [mhAPP], J20 line). We also assessed the in vivo effects of T₁AM on EC-dependent associative memory deficits, which were detected in mhAPP mice by behavioral evaluations based on the novel-object recognition paradigm. TAAR₁ expression was determined by Western blot, whereas T₁AM and its metabolite 3-iodothyroacetic acid (TA₁) were assayed by high-performance liquid chromatography coupled to mass spectrometry. Results: We demonstrate the presence of endogenous T₁AM and TAAR₁ in the EC of wild-type and mhAPP mice. Exposure to Aβ(1-42) inhibited LTP, and T₁AM perfusion (at a concentration of 5 μM, leading to an actual concentration in the perfusion buffer ranging from 44 to 298 nM) restored it, whereas equimolar amounts of 3,5,3'-triiodo-L-thyronine (T₃) and TA₁ were ineffective. The response to T₁AM was abolished by the TAAR₁ antagonist EPPTB, whereas it was mimicked by the TAAR₁ agonist RO5166017. In the EC of APPJ20 mice, LTP could not be elicited, but it was rescued by T₁AM. The intra-cerebro-ventricular administration of T₁AM (0.89 μg/kg) also restored recognition memory that was impaired in mhAPP mice. Conclusions: Our results suggest that T₁AM and TAAR₁ are part of an endogenous system that can be modulated to prevent synaptic and behavioral deficits associated with Aβ-related toxicity.

Naming difficulties after thyroid stimulating hormone suppression therapy in patients with differentiated thyroid carcinoma: a prospective cohort study

BACKGROUND

Thyroid stimulating hormone (TSH) suppression therapy after differentiated thyroid carcinoma surgery causes cognitive impairment. However, data on naming difficulties (anomia)-related specific cognitive impairment are lacking.

METHODS

A prospective cohort study was conducted, in which, patients with differentiated thyroid carcinoma and benign thyroid nodules were given oral L-T4 therapy after surgery, after meeting the criteria of TSH suppression therapy and thyroxine replacement therapy, respectively, the patients were continually given L-T4 therapy for 6 and 12 months, and then, the neuropsychological test was performed.

RESULTS

Of the 255 subjects, 212 cases (83.13%) completed all the tests, including 33 cases in the normal control group (NC group), 110 cases in the TSH suppression therapy group (TS group), and 69 cases in the thyroxine replacement therapy group (TR group). There was no significant difference in background data among the three groups (P > 0.05). The scores of mini-mental state examination, clock drawing test, digit symbol substitution test, personal history, temporal and spatial orientation, digit order relation, visual object recognition, associative learning, and color naming in the TS and TR groups were not significantly different from those in the NC group after 6 and 12 months of L-T4 therapy (P > 0.05); the scores of picture recall, visual recall, comprehension memory, and digit span forward in the TS and TR groups were notably lower than those in the NC group (P < 0.01); the scores of confrontation naming and listing the names in the TS group were significantly lower than those in the NC and TR groups, and the scores decreased with the prolongation of TSH suppression therapy (P < 0.01).

CONCLUSION

TSH suppression therapy after differentiated thyroid carcinoma surgery could lead to short-term memory impairment, attention impairment, word selection anomia, and depression, of which, word selection anomia was aggravated with the prolongation of TSH suppression therapy. Therefore, we suggested that optimal TSH goals for individual patients must balance the potential benefit of TSH suppression therapy with the possible harm from subclinical hyperthyroidism especially in low risk differentiated thyroid carcinoma patients (ClinicalTrials.gov Protocol Registration System: ClinicalTrials.gov ID NCT0266532, Registered on 21 June 2016).

Prevalence of Undiagnosed Hypothyroidism in Europe: A Systematic Review and Meta-Analysis

BACKGROUND

Patients with undiagnosed hypothyroidism are not treated for the disease and are at high risk of developing serious complications, with major impact on public health. There is a need to systematically review the available evidence on this topic.

OBJECTIVE

To identify the prevalence of undiagnosed hypothyroidism in Europe.

METHODS

A systematic review of the literature (Medline, EMBASE, and Cochrane Central) was performed to identify epidemiological studies on the prevalence of undiagnosed hypothyroidism among European populations published between January 2008 and April 2018. The Newcastle-Ottawa Scale was used to assess the methodological quality of the included studies. Random-effects meta-analyses were performed to pool estimates of proportions (with 95% confidence intervals [CIs]) of undiagnosed (1) subclinical, (2) overt, and (3) total hypothyroidism.

RESULTS

The search returned 15,565 citations (4,526 duplicates). Twenty papers were included in the study. Fourteen and 6 studies were of good and moderate methodological quality, respectively. The results of the meta-analyses were as follows for the prevalence of undiagnosed hypothyroidism: subclinical, 4.11% (95% CI 3.05-5.31%, I2 = 99.32%); overt, 0.65% (95% CI 0.38-0.99%, I2 = 96.67%); and total, 4.70% (95% CI 2.98-6.79%, I2 = 99.53%). According to the sensitivity analysis, the prevalence of hypothyroidism tends to be higher in female patients, in those aged ≥65 years, among studies with lower sample sizes, in those with thyroid-stimulating hormone levels <4.5 mIU/L, and in Eastern and Southern Europe.

CONCLUSIONS

The current evidence suggests that a considerable proportion of the European population has hypothyroidism, particularly subclinical hypothyroidism, which is undiagnosed. This issue deserves further investigation because of possible deleterious consequences for public health.

Thyroid disorders in Brazil: the contribution of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Thyroid disorders are common diseases, both in Brazil and worldwide. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a prospective cohort study that investigates cardiovascular diseases, diabetes, and associated factors, including non-classical cardiovascular risk factors such as thyroid function. Thyroid function was classified according to thyrotropin stimulating hormone (TSH), free thyroxine (FT4), and use of medication to treat thyroid disorders, after excluding participants who reported use of any medication that could alter the results of the TSH and FT4 tests. All analyses included in this review are cross-sectional using baseline data (2008 to 2010). The results showed an association of subclinical thyroid disorders with biomarkers of subclinical atherosclerosis, measured by carotid intima-media thickness and coronary artery calcium, insulin resistance, metabolic syndrome, and some psychiatric disorders. No association was found with the biomarker of inflammation high-sensitivity C-reactive protein, or changes in pulse wave velocity or heart rate variability.

The Pathology of Rapid Cognitive Decline in Clinically Diagnosed Alzheimer's Disease

BACKGROUND

Variable rate of cognitive decline among individuals with Alzheimer's disease (AD) is an important consideration for disease management, but risk factors for rapid cognitive decline (RCD) are without consensus.

OBJECTIVE

To investigate demographic, clinical, and pathological differences between RCD and normal rates of cognitive decline (NCD) in AD.

METHODS

Neuropsychology test and autopsy data was pulled from the National Alzheimer's Coordinating Center database from individuals with a clinical diagnosis of AD. Individuals with average decline of 3 or more points on the Mini-Mental Status Examination (MMSE) per year over 3 years were labeled RCD; all others were NCD.

RESULTS

Sixty individuals identified as RCD; 230 as NCD. These neuropsychology tests differed at baseline (RCD versus NCD): WMS-LM Immediate Recall (4.35[3.39] versus 6.31[3.97], p < 0.001), Animal Naming (12.1[4.83] versus 13.9[4.83], p = 0.007), TMT Part B (187[86.1] versus 159[79.0], p = 0.02), WAIS-Digit Symbol (29.5[11.3] versus 29.5[11.3], p = 0.04), and the BNT (21.5[7.05] versus 23.6[5.09], p = 0.04). RCD had more thyroid disease (30% versus 16%, p = 0.01) and greater usage of AD medication at baseline (80% versus 62%, p = 0.01). RCD had more severe cerebral amyloid angiopathy (1.62[1.0] versus 1.13[1.0], p = 0.002), more neocortical Lewy bodies (20% versus 10%, p = 0.04), and more atrophy (1.54[0.92] versus 1.17[0.83], p = 0.04). A model combining select variables was significant above chance (χ2 = 25.8, p = 0.002), but not to clinical utility (AUC < 0.70; 95% CI).

CONCLUSION

Individuals with RCD have more severe pathology, more comorbidities, and lower baseline neuropsychology test scores of language and executive function.

High Thyrotropin Is Associated with Reduced Hippocampal Volume in a Population-Based Study from Germany

BACKGROUND

Previous patient studies suggest that thyroid dysfunction affects volumes of particular regions of the brain. So far, population-based data related to this topic are lacking. The aim of this study was to investigate associations of serum levels of thyrotropin (TSH), free triiodothyronine, and free thyroxine (fT4) with total brain volume, gray matter volume, white matter volume (WMV), and hippocampal volume (HV) in a population-based study.

METHODS

Data on 2557 individuals were pooled from two independent population-based surveys of the Study of Health in Pomerania conducted in Northeast Germany. Brain volumes were determined from images derived from 1.5 T magnetic resonance imaging. Low and high TSH were defined using the cutoffs 0.40 and 3.29 mIU/L, respectively. Associations between thyroid hormone levels and segmented brain volumes were analyzed by linear regression models. Further, voxel-based morphometry was conducted to search for associations with thyroid hormone levels in a hypothesis-free way throughout the whole brain. All models were adjusted for confounders.

RESULTS

Only 9/70 individuals with high TSH had low free triiodothyronine or fT4 levels. Individuals with high TSH had significantly lower total brain volume (β = -26.9 [confidence interval (CI) -49.0 to -4.8]; p = 0.017), WMV (β = -16.1 [CI -29.4 to -2.7]; p = 0.018), and HV (β = -223 [CI -395 to -50]; p = 0.011) than individuals with TSH within the reference range, while low TSH was not significantly associated with any of the brain volumes. Voxel-based morphometry analyses revealed a significant positive association with serum fT4 levels in the left middle frontal gyrus.

CONCLUSIONS

In conclusion, the results of this study indicate that the subclinical hypothyroid state may lead to a reduced brain volume affecting particularly HV in younger subjects and WMV, which might correspond to subtle microstructural changes in white matter fiber tracts or myelination of the axones. Gray matter seems not to be affected by subclinical hypothyroid states.

The association between adherence to levothyroxine and economic and clinical outcomes in patients with hypothyroidism in the US

OBJECTIVE

To evaluate outcomes associated with adherence to levothyroxine (LT4) in the US adult hypothyroidism population.

METHODS

We used data from Truven's MarketScan databases from 1 July 2011 through 31 December 2015. Patients aged 18 or older were diagnosed with hypothyroidism (confirmed at least twice) and prescribed LT4. Patients were excluded if they did not have continuous insurance coverage or if they received a diagnosis of thyroid cancer or pregnancy during the study period. Multivariable analyses on a matched cohort of adherent and nonadherent patients examined the relationships among patient outcomes and adherence, defined as the proportion of days covered ≥80%. Outcomes included all-cause and hypothyroidism-related medical costs and resource utilization and comorbid diagnoses measured over the 1 year post-period following the first prescription for LT4. The analyses controlled for patient age, sex, region of residence, type of insurance coverage, diagnosing physician and pre-period general health status as proxied by the Charlson Comorbidity Index.

RESULTS

Prior to matching, there were 168,457 patients identified as adherent and 198,443 patients identified as nonadherent. The matched cohort consisted of 318,628 individuals, with equal numbers of adherent and nonadherent patients (n = 159,314). Patients who were adherent used significantly fewer resources and had significantly lower all-cause ($14,136 vs. $14,926; p < .0001) and hypothyroidism-related ($1672 vs. $1709; p < .0001) total costs, although the costs of drugs were higher in the adherent group. Furthermore, adherent patients, compared to nonadherent patients, were significantly less likely to be diagnosed with comorbid Addison's disease, bipolar disorder, chronic kidney disease, depression, migraine, obesity, type 1 diabetes or type 2 diabetes during the follow-up period.

CONCLUSIONS

Compared to nonadherence, adherence to LT4 among patients with hypothyroidism was associated with a significant reduction in all-cause and hypothyroidism-related costs and resource utilization as well as significantly lower rates of many comorbid diagnoses.

Evaluation of Cognitive Function in Patients with Type 2 Diabetes and Overt Hypothyroidism

Background and Aims. Previous studies report the presence of cognitive impairment in patients with overt hypothyroidism. The thyroid hormones are essential for neurological and intellectual functions. Type 2 diabetes mellitus (T2DM) subjects are exposed to higher risk of cognitive function alteration compared to nondiabetic subjects. The aim of the present study was to analyze the cognitive function of T2DM subjects with overt hypothyroidism.

Materials and Methods. We performed an observational study between 2015-2017. A total of 12 patients (11 women and 1 men) with overt hypothyroidism and T2DM were recruited for this study. Their cognitive function was compared with that of subjects of a control group (16 patients - 12 women and 4 men with T2DM but without overt hypothyroidism). Cognitive function was evaluated using the Mini Mental State Examination (MMSE) test. Serum thyroid stimulating hormone (TSH) levels were measured by immunoradiometric assay, free thyroxine (FT4) by radioimmunoassay while fasting plasma glucose (FPG) levels were evaluated using automated devices.

Results. There were no significant differences between the two groups in respect of age and FPG. In the study group, mean TSH and FT4 levels were 11.76±4.43 mIU/L, resepectively 0.53±0.08 ng/dL while in the control group these were 2.60±0.40 mIU/L, respectively 1.12±0.19 ng/dL (p<0.001). Moderate cognitive impairment was present in 3 patients of the study group (25.00%) and in 2 subjects from the control group (12.50%). Mild cognitive impairment was present in 4 patients (33.33%) of the study group and in 2 subjects from the control group (12.50%).

Conclusion. This study showed that MMSE scores are significantly reduced in subjects with T2DM and hypothyroidism compared to subjects with T2DM without hypothyroidism (p<0.004). The study revealed a negative correlation between TSH and MMSE score in the study group.

Alteration in intrinsic and extrinsic functional connectivity of resting state networks associated with subclinical hypothyroid

Subclinical hypothyroidism (SCH) is characterized by mild elevation of thyroid stimulating hormone (TSH) (range 5-10 μIU/ml) and normal free triiodothyronine (FT3) and free thyroxine (FT4). The cognitive function impairment is well known in thyroid disorders such as hypothyroidism and hyperthyroidism, but little is known about deficits in brain functions in SCH subjects. Also, whether hormone-replacement treatment is necessary or not in SCH subjects is still debatable. In order to have an insight into the cognition of SCH subjects, intrinsic and extrinsic functional connectivity (FC) of the resting state networks (RSNs) was studied. For resting state data analysis we used an unbiased, data-driven approach based on Independent Component Analysis (ICA) and dual-regression that can emphasize widespread changes in FC without restricting to a set of predefined seeds. 28 SCH subjects and 28 matched healthy controls (HC) participated in the study. RSN analysis showed significantly decreased intrinsic FC in somato-motor network (SMN) and right fronto-parietal attention network (RAN) and increased intrinsic FC in default mode network (DMN) in SCH subjects as compared to control subjects. The reduced intrinsic FC in the SMN and RAN suggests neuro-cognitive alterations in SCH subjects in the corresponding functions which were also evident from the deficit in the neuropsychological performance of the SCH subjects on behavioural tests such as digit span, delayed recall, visual retention, recognition, Bender Gestalt and Mini-Mental State Examination (MMSE). We also found a significant reduction in extrinsic network FC between DMN and RAN; SMN and posterior default mode network (PDMN); and increased extrinsic FC between SMN and anterior default mode network (ADMN) in SCH subjects as compared to controls. An altered extrinsic FC in SCH suggests functional reorganization in response to neurological disruption. The partial correlation analysis between intrinsic and extrinsic RSNs FC and neuropsychological performances as well as clinical indices give interesting insights into brain-behavior relationship in SCH subjects. This article is protected by copyright. All rights reserved.

Thyrotropin level and cognitive performance: Baseline results from the ELSA-Brasil Study

BACKGROUND AND AIMS

The role of subtle thyroid alterations, such as subclinical thyroid disease and low/high serum thyrotropin (TSH) within the normal range, on cognitive decline is controversial. The aim of this study was to evaluate the association of serum TSH and subclinical thyroid dysfunction with performance on cognitive tests in a large sample of Brazilian middle-aged adults without overt thyroid disease.

METHODS

In this cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health, we excluded individuals aged 65 years and older, with overt thyroid dysfunction, prevalent stroke, in use of medications that affect thyroid function or that indicate neurologic diseases, and from Asian or indigenous ethnicity. Thyroid status was assessed by serum TSH and free thyroxine (only when the TSH was altered). Individuals were divided according to TSH tertiles and classified according to thyroid function as euthyroidism, subclinical hypothyroidism, or subclinical hyperthyroidism. Cognition was evaluated using delayed word recall test, semantic verbal fluency test, and trail making test version B. The associations of cognitive tests performance with TSH tertiles (using the middle tertile as reference) and thyroid function were investigated using linear regression models, adjusted for an extensive set of possible confounders (sociodemographic characteristics, cardiovascular risk factors, and depression).

RESULTS

The mean age of the 10,362 participants was 49.5±7.4years, 52.3% women. After adjustment for confounders, the first TSH tertile was associate with worse performance on the trail making test (β=-0.05, 95% CI=-0.09; -0.01, p=0.017). When restricting the analysis to the 9769 individuals with TSH within the normal range, the association between TSH and performance on the trail making test remained significant (β=-0.05, 95% CI=-0.09; -0.01, p=0.020) on multiple linear regression. Subclinical thyroid disease was not associated with performance on cognitive tests.

CONCLUSION

Low TSH is associated with poorer performance on an executive function test in middle-aged adults without overt thyroid dysfunction.

The association between subclinical thyroid dysfunction and dementia: The Health, Aging and Body Composition (Health ABC) Study

OBJECTIVE

Data on the association between subclinical thyroid dysfunction and dementia are limited and conflicting. We aimed to determine whether subclinical thyroid dysfunction was associated with dementia and cognitive decline.

DESIGN

Population-based prospective cohort study.

PATIENTS

Adults aged 70-79 years with measured thyroid function, but no dementia at baseline, and Modified Mini-Mental State (3MS) at baseline and follow-up.

MEASUREMENTS

Primary outcome was incident-adjudicated dementia, based on 3MS, hospital records and dementia drugs. Secondary outcome was change in 3MS. Models were adjusted for age, sex, race, education and baseline 3MS, and then further for cardiovascular risk factors.

RESULTS

Among 2558 adults, 85% were euthyroid (TSH 0.45-4.49mIU/L), 2% had subclinical hyperthyroidism with mildly decreased TSH (TSH 0.10-0.44 mIU/L), 1% subclinical hyperthyroidism with suppressed TSH (TSH < 0.10 mIU/L with normal free thyroxine [FT4]) and 12% subclinical hypothyroidism (TSH 4.50-19.99 mIU/L with normal FT4). Over 9 years, 22% developed dementia. Compared to euthyroidism, risk of dementia was higher in participants with subclinical hyperthyroidism with suppressed TSH (HR 2.38, 95% CI = 1.13;5.04), while we found no significant association in those with mildly decreased TSH (HR 0.79, 95% CI = 0.45;1.38) or with subclinical hypothyroidism (HR 0.91, 95% CI = 0.70;1.19). Participants with subclinical hyperthyroidism with suppressed TSH had a larger decline in 3MS (-3.89, 95% CI = -7.62; -0.15).

CONCLUSIONS

Among older adults, subclinical hyperthyroidism with a TSH < 0.10 mIU/L was associated with a higher risk of dementia and a larger cognitive decline, while subclinical hyperthyroidism with mildly decreased TSH or subclinical hypothyroidism were not.