Cognitive function in subclinical hypothyroidism in elderly

Association of thyroid disease with risks of dementia and cognitive impairment: A meta-analysis and systematic review

Introduction

It is still uncertain whether the risk of dementia and cognitive impairment is related to thyroid disease. we carried out a meta-analysis and systematic review (PROSPERO: CRD42021290105) on the associations between thyroid disease and the risks of dementia and cognitive impairment.

Methods

We searched PubMed, Embase, and Cochrane Library for studies published up to August 2022. The overall relative risk (RRs) and its 95% confidence interval (CIs) were calculated in the random-effects models. Subgroup analyses and meta-regression were conducted to explore the potential source of heterogeneity among studies. We tested and corrected for publication bias by funnel plot-based methods. The Newcastle-Ottawa Scale (NOS) or Agency for Healthcare Research and Quality (AHRQ) scale were used to evaluate the study quality of longitudinal studies and cross-sectional studies, respectively.

Results

A total of 15 studies were included in our meta-analysis. Our meta-analysis showed that hyperthyroidism (RR = 1.14, 95% CI = 1.09–1.19) and subclinical hyperthyroidism (RR = 1.56, 95% CI = 1.26–1.93) might be associated with an elevated risk for dementia, while hypothyroidism (RR = 0.93, 95% CI = 0.80–1.08) and subclinical hypothyroidism (RR = 0.84, 95% CI = 0.70–1.01) did not affect the risk.

Discussion

Hyperthyroidism and subclinical hyperthyroidism are predictors of dementia.

Systematic review registration

PROSPERO, Identifier: CRD42021290105.

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.

Effect of Levothyroxine Replacement on Cognitive Function Impairment in a Sample of Egyptian Population with Subclinical Hypothyroidism

<b><i>Introduction:</i></b> Subclinical hypothyroidism (SHT) is characterized by a normal range of free thyroxin concentrations together with increased serum TSH levels. SHT is defined as serum thyroid-stimulating hormone (TSH) concentration above the upper limit of the reference range in the face of normal free FT4 and FT3 levels. The effect of SHT on cognitive function has been investigated in several preclinical studies, and a growing body of evidence has suggested a relevant link between thyroid hormones and the central nervous system. <b><i>Objectives:</i></b> This study aimed to investigate the effect of levothyroxine replacement on cognitive impairment in a sample of Egyptian patients with SHT. <b><i>Methods:</i></b> A prospective cohort study conducted on 30 patients with cognitive impairment and SHT attending an endocrine outpatient clinic at the Ain Shams University Hospital to study the effect of levothyroxine supplementation on cognitive impairment in patients with SHT. The study was conducted on 30 patients. All participants were subjected to a full history taking; thorough clinical examination; laboratory investigations including thyroid profile (FT3, FT4, TSH), anti-thyroid peroxidase antibodies, anti-thyroglobulin antibodies, and lipid profile; imaging tests as neck ultrasound, echocardiography, and carotid duplex; and finally Addenbrooke’s questionnaire used to diagnose mild cognitive impairment. <b><i>Results:</i></b> A highly statistically significant difference was found before, 3 months and 6 months after treatment with levothyroxine regarding all clinical data, TSH, LDL, T. cholesterol, FT3, FT4 and HDL, carotid intima-media thickness, and Addenbrooke’s questionnaire. Our study showed a statistically significant inverse correlation between TSH level and mild cognitive impairment before and after treatment with levothyroxine at 3 and 6 months intervals as when TSH increased, results of Addenbrooke’s questionnaire decreased and, so, cognitive impairment increased, while when TSH decreased in response to thyroxine replacement, cognitive impairment improved as detected by an increase in the patient’s score. <b><i>Conclusion:</i></b> SHT has a great effect on cognitive impairment, as normalization in TSH level results in improvement in cognitive function. Also, there was a significant reduction in carotid intima-media thickness, which may contribute to improvement of cognitive function in addition to a great improvement in lipid profile, which in turn positively affects cardiac and cognitive function.

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.

Diagnosis and Management of Hypothyroidism: Addressing the Knowledge-Action Gaps

Hypothyroidism presents a large epidemiological burden in India. As a result of subtle and nonspecific clinical symptoms and signs, the condition often goes undiagnosed and is not adequately treated when it is detected. There is heterogeneity in the diagnostic and treatment approaches to hypothyroidism. As a result of the physiological changes in thyroid hormones with age and illness, it is important to tailor the diagnosis and management of this condition in specific populations including pregnant women, infants, children, geriatric patients, and those with comorbid conditions. Enhanced understanding and education of physicians and patients can help to improve the outcomes of treatment in hypothyroidism which should be focused on patient-centered care. Policies and reforms should be crafted and implemented at the national level to curb public health challenges of hypothyroidism. This publication summarizes the recommendations of a national advisory board meeting to identify and bridge the gaps in understanding of the diagnosis and treatment of hypothyroidism in India. As a complement to clinical judgment, these recommendations will foster the diagnosis and management of hypothyroidism in the community and clinics for the benefit of the patients.

FUNDING

Merck Ltd, India.

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.

High levels of Nesfatin-1 in relation to the dysfunction of the hypothalamic-pituitary-adrenal and hypothalamus-pituitary-thyroid axes in depressed patients with subclinical hypothyroidism

Despite the increasing amount of evidence suggesting a relationship between depression and subclinical hypothyroidism (SCH), the exact mechanism underlying this relationship remains unclear. The main purpose of this study was to investigate the roles of plasma Nesfatin-1 levels and dysfunction of the hypothalamic-pituitary-adrenal (HPA) and hypothalamus-pituitary-thyroid (HPT) axes in the comorbidity of depression and SCH. Dysfunctions of the HPA and HPT axes were detected by measuring plasma corticosterone and thyroid-stimulating hormone (TSH) concentrations, respectively. Subjects in the patient group were selected from patients hospitalized at the Anhui Mental Health Center, and subjects in the control group were recruited from healthy volunteers. Healthy control subjects were matched to the patients in terms of weight and body mass index. The Hamilton Depression Rating Scale was administered to both the groups. The enzyme-linked immunosorbent assay method was used to measure plasma Nesfatin-1, corticosterone, and TSH levels. A radioimmunoassay kit was used for the measurement of the plasma-free triiodothyronine and plasma-free thyroxine. The results showed that the Hamilton Depression Rating Scale scores and average Nesfatin-1, corticosterone, and TSH levels were significantly higher in depressed patients with SCH than in the control group. Moreover, positive relationships were observed between Nesfatin-1 levels and the concentrations of corticosterone (r=0.626, P<0.001) and TSH (r=0.229, P=0.036) in depressed patients with SCH. These findings indicate that Nesfatin-1 is involved in the comorbidity of depression and SCH, and the mechanism underlying this involvement might be related to the dysfunction of the HPA and HPT axes.

Is There Any Effect on Smell and Taste Functions with Levothyroxine Treatment in Subclinical Hypothyroidism?

Subclinical hypothyroidism has been accused for coronary heart disease, lipid metabolism disorders, neuropsychiatric disorders, infertility or pregnancy related problems with various strength of evidence. Currently there is insufficient knowledge about olfaction and taste functions in subclinical hypothyroidism. Aim of the present study is to investigate the degree of smell and taste dysfunction in patients with subclinical hypothyroidism. 28 subclinical hypothyroid patients, and 31 controls enrolled in the prospective study in Istanbul, Turkey. Subclinical hypothyroid patients were treated with L-thyroxine for 3 months. Psychophysiological olfactory testing was performed using odor dispensers similar to felt-tip pens (“Sniffin’ Sticks”, Burghart, Wedel, Germany). Taste function tests were made using "Taste Strips" (Burghart, Wedel, Germany) which are basically tastant adsorbed filter paper strip. Patients scored lower on psychophysical olfactory tests than controls (odor thresholds:8.1±1.0 vs 8.9±1.1, p = 0.007; odor discrimination:12.4±1.3 vs 13.1±0.9, p = 0.016; odor identification:13.1±0.9 vs 14.0±1.1, p = 0.001; TDI score: 33.8±2.4 vs 36.9±2.1, p = 0.001). In contrast, results from psychophysical gustatory tests showed only a decreased score for “bitter” in patients, but not for other tastes (5.9±1.8 vs 6.6±1.0, p = 0.045). Three month after onset of treatment olfactory test scores already indicated improvement (odor thresholds:8.1±1.0 vs 8.6±0.6, p<0.001; odor discrimination:12.4±1.31 vs 12.9±0.8, p = 0.011; odor identification:13.1±0.9 vs 13.9±0.8, p<0.001; TDI scores:33.8±2.4 vs 35.5±1.7, p<0.001) respectively. Taste functions did not differ between groups for sweet, salty and, sour tastes but bitter taste was improved after 3 months of thyroxin substitution (patients:5.9±1.8 vs 6.6±1.2, p = 0.045). Correlation of changes in smell and taste, with thyroid function test were also evaluated. TSH, fT4 were found have no correlation with smell and taste changes with treatment. However bitter taste found positively correlated with T3 with treatment(r: 0.445, p: 0.018). Subclinical hypothyroid patients exhibited a significantly decreased olfactory sensitivity; in addition, bitter taste was significantly affected. Most importantly, these deficits can be remedied on average within 3 months with adequate treatment.

Resveratrol improved the spatial learning and memory in subclinical hypothyroidism rat induced by hemi-thyroid electrocauterization

The major purpose of this study was to investigate the effect of resveratrol (RES) on the spatial learning and memory ability in subclinical hypothyroidism (SCH) rat model and the potential mechanism. A SCH rat model was induced by hemi-thyroid electrocauterization and the activity of hypothalamus-pituitary-thyroid (HPT) axis was detected. The spatial learning and memory ability was tested using Morris water maze (MWM) and Y-maze. The protein expressions of synaptotagmin-1 (syt-1) and brain-derived neurotrophic factor (BDNF) in the hippocampus were measured via western blot. The results showed that SCH rat model was successfully duplicated. The SCH rats showed impaired learning and memory in the behavioral tests. However, these changes were reversed by the treatment of RES (15mg/kg) and levothyroxine (LT4). Moreover, RES treated rats exhibited reduced plasma TSH level and hypothalamic thyrotropin releasing hormone (TRH) mRNA expression, which suggested that the imbalance of HPT axis in the SCH rats could be reversed by RES treatment. Furthermore, RES treatment up-regulated the protein levels of syt-1 and BDNF in hippocampus. These findings indicated an amelioration effect of RES on the spatial learning and memory in the SCH rats, the mechanism of which might be involved with its ability of modifying the hyperactive HPT axis and up-regulating the hippocampal hypo-expression of syt-1 and BDNF.