Association between a serum thyroid-stimulating hormone concentration within the normal range and indices of obesity in Japanese men and women

Development and basic performance verification of a rapid homogeneous bioassay for agonistic antibodies against the thyroid-stimulating hormone receptor

Graves' disease is a type of autoimmune hyperthyroidism caused by thyroid-stimulating antibodies (TSAb).1 The combination of a porcine thyroid cell bioassay and cyclic adenosine monophosphate (cAMP) immunoassay (TSAb-enzyme immunoassay; EIA) is a clinically approved TSAb measurement method. Due to the requirement of multiple procedures and a long assay time of 6 h in the TSAb-EIA, a simplified and rapid assay is desired. Herein, we developed a rapid homogeneous TSAb bioassay (rapid-TSAb assay) using the human embryonic kidney cell line (HEK293), engineered to express the human thyroid-stimulating hormone receptor (TSHR), along with a cAMP-dependent luminescence biosensor. The measurement consists of three steps: thawing frozen cells, blood sample addition, and luminescence detection. The procedures can be conducted within 1 h. The World Health Organization International Standard TSAb (NIBSC 08/204) stimulated the cells co-expressing TSHR and cAMP biosensor. The intra- and inter-assay coefficients of variance were < 10%. Stimulation activity using wild-type TSHR and chimeric TSHR (Mc4) almost completely correlated with the tested Graves' disease and normal samples. In the rapid-TSAb assay, the evaluation of 39 samples, including TSHR antibody-positive sera, yielded a sensitivity of 100.0% and a specificity of 90.9%, compared to the TSAb-EIA control. The rapid-TSAb assay enables simple and rapid measurement of TSAb and is promising for improving the diagnosis of autoimmune thyroid diseases.

Pituitary crosstalk with bone, adipose tissue and brain

Traditional textbook physiology has ascribed unitary functions to hormones from the anterior and posterior pituitary gland, mainly in the regulation of effector hormone secretion from endocrine organs. However, the evolutionary biology of pituitary hormones and their receptors provides evidence for a broad range of functions in vertebrate physiology. Over the past decade, we and others have discovered that thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotropic hormone, prolactin, oxytocin and arginine vasopressin act directly on somatic organs, including bone, adipose tissue and liver. New evidence also indicates that pituitary hormone receptors are expressed in brain regions, nuclei and subnuclei. These studies have prompted us to attribute the pathophysiology of certain human diseases, including osteoporosis, obesity and neurodegeneration, at least in part, to changes in pituitary hormone levels. This new information has identified actionable therapeutic targets for drug discovery.

Thyroid-Related Hormones Changes Predict Changes in Anthropometric Measures and Incidence of Obesity in Chinese Euthyroid Persons

The purpose of this study was to investigate the correlation of thyroid-related hormones changes within the reference range with the changes in anthropometric measures and incidence of obesity. The study included 4850 subjects with normal thyroid-related hormones at baseline and at follow-up. We evaluated the relationship of changes in thyroid-related biomarkers with anthropometric measures changes and incidence of obesity. In euthyroid persons, changes in serum thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) concentrations and FT3/FT4 ratio were independent predictors of changes in body mass index (BMI) and waist circumference (WC) in men, changes in serum FT3 and FT4 concentrations and FT3/FT4 ratio were independent predictors of changes in BMI and WC in women. Every single unit increment in ΔFT3/FT4 was accompanied by a 7.144 and 7.572 times risk of having obesity in men and women, respectively. Every single unit decrement in ΔFT4 was accompanied by a 21.0% and 26.9% lower risk of having obesity in men and women, respectively. In conclusion, in euthyroid individuals, changes in thyroid-related hormones were associated with anthropometric measures changes and incidence of obesity.

Association between High Normal TSH Levels and Obesity in Women with Anti-Thyroid Autoantibodies (ATAs)

A positive correlation between Thyroid-Stimulating Hormone (TSH) and Body Mass Index (BMI) has been reported in many studies, but data on this topic remain controversial, especially when TSH values are in the normal range. Moreover, few studies have evaluated the co-existence of thyroid autoimmunity. This study investigated the role of thyroid autoimmunity in the interconnection between TSH, BMI, and waist circumference (WC) in euthyroid patients with overweight or obesity. We enrolled 902 patients (213 males; mean age ± SD: 45 ± 14 years; mean BMI ± SD: 35.8 ± 6.5 kg/m²), with normal serum TSH concentration; anti-thyroid autoantibodies (ATAs) were evaluated in 752 patients (186 males). Patients were divided into four BMI classes, based on WHO criteria, and the relationship between BMI, WC, and TSH was evaluated in the whole sample and compared to ATAs positivity, observed in 235 patients (44 males). No significant difference was found between TSH levels in the BMI classes. A statistically significant correlation between TSH and BMI was found only in ATAs-positive females (N = 191, Spearman rho: 0.149; p-value: 0.040). However, this finding was not confirmed when considering the WC. Our study shows a positive correlation only between TSH and BMI in obese women with positive ATAs, suggesting that in these patients, the high normal levels of TSH could be attributed to a mild thyroid failure with a possible worsening obesity-related effect, and both need a careful evaluation.

The Effects of Zinc and Selenium Supplementation on Body Composition and Thyroid Function in Individuals with Overweight or Obesity: A Systematic Review

People with obesity have been found to have lower zinc (Zn) and selenium (Se) circulatory levels and abnormal thyroid function than people with normal weight. Studies about the effects of Zn and Se supplementation on body composition and thyroid function of overweight-obese people showed inconsistent results. A systematic review of randomized controlled trials was conducted to determine the effects of Ζn supplementation, Se supplementation, and their combination on body composition and thyroid function of individuals with overweight or obesity. Databases of PubMed, ScienceDirect, and Cochrane, were searched from inception to February 27, 2022, to identify relevant articles. For the assessment of the methodological quality of the studies, the Jadad scale was used. After screening the articles, thirteen studies were finally included and were analyzed using the strength of the evidence approach. Regarding the effectiveness of Zn supplementation on body composition, moderate evidence was found, while the effects of Se were found to be mixed. Zn supplementation was found to affect the thyroid function of people with overweight or obesity by increasing their free triiodothyronine (FT3) levels. However, this result is based only on one study among hypothyroid patients. At this point, the effectiveness of Zn, Se, and their combination, on the body composition and the thyroid function of people with overweight or obesity cannot safely be determined because of the controversial results, small number, and the limitations of the identified studies. The results of this systematic review must be interpreted with caution due to the limitations detected.

Is There a Relationship Between Vascularity and Echogenicity of Thyroid Lobes in Ultrasonography With BMI? A Large Retrospective Cohort Study

Objective:

The aim of this study was to investigate the relationship between sonographic vascularity and echogenicity of the thyroid lobes, compared with a participant’s body mass index (BMI).

Materials and Methods:

A total of 3722 participations, with varied BMI, were included in the study. For all the participants, the thyroid-stimulating hormone (TSH) was measured, as well as thyroid volume, sonographic echogenicity, and vascularity were recorded. A multiple regression analysis was performed to assess the relationship between the sonographic vascularity and echogenicity, of thyroid lobes, compared with the participants’ BMI.

Results:

The serum TSH values were significantly higher in patients with a BMI > 25 kg/m². The sonographic vascularity and volume of thyroid lobes were positively correlated the participants’ BMI ( P < .005). Sonographic heterogenicity of the left thyroid lobe, right thyroid lobe, and the isthmus were positively associated with BMI ( P < .005). However, the hyper/hypoechogenicity did not demonstrate any significant correlation with BMI ( P > .005).

Conclusion:

Based on the findings of this study, it was concluded that thyroid volumes may have a significant positive relationship with BMI. In overweight participants (i.e., BMI more than 25), thyroid echogenicity was more heterogeneous and their thyroid lobes were more hypovascular.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

Investigating the prevalence of primary thyroid dysfunction in obese and overweight individuals: Tehran thyroid study

BACKGROUND

Due to the increasing worldwide prevalence of obesity, it is essential to determine the prevalence of obesity-related thyroid dysfunctions. The purpose of this study was to investigate the prevalence of thyroid dysfunctions, namely hypothyroidism and hyperthyroidism, and their association with BMI among adult Iranian overweight and obese individuals.

METHOD

This cross-sectional study was carried out within the framework of the Tehran Thyroid Study (TTS); 5353 participants (57.5% female) entered our study. Anthropometric measurements were performed. Serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid peroxidase antibody (TPOAb) were assayed. We categorized individuals into 3 BMI groups (normal-weight, overweight and obese), then calculated prevalence rate, odds ratio (OR), and 95% confidence interval (CI) for outcomes in overweight and obese groups. The normal-weight group was used as the control group.

RESULTS

We found a higher prevalence of hypothyroidism (11.6% vs 8.2% Total, 4.0% vs 1.1% overt and 7.6% vs 7.1% subclinical, P < 0.001) and TPOAb positivity (17.3% vs 11.6%, P < 0.001) in obese participants compared with normal-weight participants. Hyperthyroidism's overall prevalence was 4.2, 5.7, and 4.9% in obese, overweight, and normal-weight groups, respectively. Obesity was associated with higher odds of overt hypothyroidism (OR: 2.0, 95% CI: 1.15-3.49, P < 0.05) and TPOAb positivity (OR: 1.29, 95% CI: 1.04-1.60, P < 0.05) after adjusting for confounding variables. In contrast, no association was observed between the overweight group and the odds of hypothyroidism and TPOAb positivity in the adjusted results.

CONCLUSIONS

Obesity was associated with an increased risk of overt hypothyroidism and TPOAb positivity.

The Relationship Between Metabolic Parameters, Age, and Thyroid Status: A Cross-Sectional Study-Based National Survey of Iodine Nutrition, Thyroid Disease

Aim

The relationship between thyroid status and metabolic factors was investigated as well as iodine nutrition in the general population and among the elderly population.

Methods

We performed a cross-sectional survey of 2483 subjects to assess the status of national iodine nutrition and incidence of thyroid disease. The general and elderly populations were divided into normal thyroid function (NTF) and subclinical hypothyroidism (SCH) groups. The anthropometric parameters and biochemical indicators were then analyzed.

Results

Overall, 327 participants were diagnosed with thyroid diseases, 73 (22.32%) of whom were 65 years or older. For the general population, compared with the NTF group, individuals in the SCH group were older, presented with higher systolic blood pressure, fasting blood glucose, serum cholesterol, and urinary iodine concentration (all p<0.05) but lower blood uric acid (UA) (p<0.05). Linear regression analysis further revealed that age and triglyceride (TG) serum levels positively correlated with serum thyroid-stimulating hormone (TSH) levels. Multiple regression analyses revealed that age, TG, waist circumference (WC), and body mass index were independent predictors for abnormal TSH serum levels. For the elderly population, compared with NTF group, individuals in the SCH group were substantially older (p<0.05) but presented with lower UA (p<0.05). Pearson linear regression analysis revealed a positive correlation between age (p=0.003) as well as TG levels (p<0.001) and serum TSH levels. In contrast, WC (p=0.003) was negatively related to TSH serum levels. Further multiple regression analysis revealed that age, TG, WC and heart rate were independent predictors of blood TSH.

Conclusion

The large-scale national study of iodine nutrition, thyroid disease has shown a vital relationship between metabolic indicators and serum TSH levels. Age and metabolic diseases increase the likelihood of developing thyroid diseases, both the general population and among the elderly.

Interaction effect of obesity and thyroid autoimmunity on the prevalence of hyperthyrotropinaemia

PURPOSE

The role of thyroid autoimmunity in the association between obesity and hyperthyrotropinaemia remains unclear. We aimed to assess the relationship between obesity, autoimmunity, and hyperthyrotropinaemia.

METHODS

In this population-based cross-sectional study, 12531 Chinese individuals (18-80 years) with thyroid function test were categorized into three groups by body mass index (BMI) and were categorized into three layers by thyroid autoantibodies. Multivariate logistic regression was employed to assess the correlation and interaction effect.

RESULTS

There was no significant difference in prevalence of hyperthyrotropinaemia (P = 0.637) among three BMI groups. After stratification, the difference of serum thyrotropin (P < 0.01) and prevalence of hyperthyrotropinaemia (P < 0.01) between the three groups have significant linear trends at the positive levels of thyroid peroxidase antibody (TPOAb) or/and thyroglobulin antibody (TgAb). When TPOAb and TgAb were positive, the risk of hyperthyrotropinaemia increased 1.857-fold in overweight group and 2.201-fold in obese group compared with normal group. Compared with negative TPOAb and TgAb, the risk of hyperthyrotropinaemia for individuals with two positive antibodies increased 3.310-fold, 4.969-fold, and 5.122-fold in the three BMI groups. The adjusted OR (95% CI) for interaction were 1.033 (0.752-1.419) for overweight and one positive antibodies, 1.935 (1.252-2.990) for overweight and two positive antibodies, 1.435 (0.978-2.105) for obesity and one positive antibodies and 2.191 (1.252-3.832) for obesity and two positive antibodies.

CONCLUSION

Overweight and obesity were associated with hyperthyrotropinaemia only in presence of thyroid autoimmunity, and obesity might aggravate the pathogenic effect of autoimmunity on hyperthyrotropinaemia. There was an interaction effect between obesity and autoimmunity on the prevalence of hyperthyrotropinaemia.

The role of thyroid hormone in metabolism and metabolic syndrome

Metabolic syndrome (MetS) and thyroid dysfunction are common in clinical practice. The objectives of this review are to discuss some proposed mechanisms by which thyroid dysfunctions may lead to MetS, to describe the bidirectional relationship between thyroid hormones (THs) and adiposity and finally, to resume a list of recent studies in humans that evaluated possible associations between thyroid hormone status and MetS or its clinical components. Not solely THs, but also its metabolites regulate metabolic rate, influencing adiposity. The mechanisms enrolled are related to its direct effect on adenosine triphosphate (ATP) utilization, uncoupling synthesis of ATP, mitochondrial biogenesis, and its inotropic and chronotropic effects. THs also act controlling core body temperature, appetite, and sympathetic activity. In a bidirectional way, thyroid function is affected by adiposity. Leptin is one of the hallmarks, but the pro-inflammatory cytokines and also insulin resistance impact thyroid function and perhaps its structure. MetS development and weight gain have been positively associated with thyroid-stimulating hormone (TSH) in several studies. Adverse glucose metabolism may be related to hyperthyroidism, but also to reduction of thyroid function or higher serum TSH, as do abnormal serum triglyceride levels. Hypo- and hyperthyroidism have been related to higher blood pressure (BP), that may be consequence of genomic or nongenomic action of THs on the vasculature and in the heart. In summary, the interaction between THs and components of MetS is complex and not fully understood. More longitudinal studies controlling each of all confounding variables that interact with endpoints or exposure factors are still necessary.

Association between TSH levels within the reference range and adiposity markers at the baseline of the ELSA-Brasil study

Background

The association of thyrotropin (TSH) with overall (body mass index, BMI), visceral (waist circumference and steatosis), and upper subcutaneous (neck circumference, NC) adiposity markers is still controversial, and the aim of this study is to assess these associations in the baseline data of a large cohort from ELSA-Brasil.

Methods and findings

This cross-sectional study included 11,224 participants with normal thyroid function (normal TSH levels). BMI, waist circumference, NC and steatosis, defined by hepatic attenuation (mild or moderate/severe) were the explicative variables. TSH levels were log transformed (logTSH), and multivariate linear regression models were generated to estimate the associations between logTSH and BMI (continuous and categorized), waist circumference, NC, and steatosis after adjusting for sociodemographic characteristics, health behaviors, and comorbidities. The mean age was 51.5±8.9 years, 5,793 (51.6%) participants were women, 21.8% (n = 2,444) were obese, and 15.1% of the sample was TPOAb positive. The TSH levels were significantly higher in the obese group than in the reference group (<25.0 kg/m²). In the multivariable linear regression models, significant associations of logTSH with BMI and obesity were found. LogTSH was associated with waist circumference only among women. NC and steatosis were not related to TSH levels.

Conclusions

TSH levels were associated with overall adiposity and obesity. Further studies may elucidate reference levels of TSH according to BMI status.

The Association Between Serum Thyrotropin Within the Reference Range and Metabolic Syndrome in a Community-Based Chinese Population

PURPOSE

We aimed to ascertain the association between thyrotropin (TSH) levels in euthyroid state and the prevalence of metabolic syndrome (MetS) in a community-based Chinese population.

PARTICIPANTS AND METHODS

Based on a large and well-characterized community cohort in Beijing, China, 1831 men and 1742 women with serum TSH levels within the reference range (0.50-4.78 µIU/mL) were stratified by quartiles of TSH (Q1-4). MetS was identified according to the criteria of International Diabetes Federation guidelines. Poisson regression models were used to estimate the association between serum TSH and the prevalence of MetS and its components before and after adjustment for potential confounding factors. The reported association was measured using the prevalence ratio (PR) with its respective 95% confidence interval (95% CI).

RESULTS

The prevalence of MetS in euthyroid population across TSH quartiles (Q1-4) was 38.9%, 44.6%, 41.0%, and 47.7%, respectively, in men (P = 0.045), and 47.7%, 46.6%, 46.9%, and 54.6%, respectively, in women (P = 0.032). Compared with the reference group TSH-Q1, the prevalence of MetS was higher among TSH-Q4 group both in men (PR = 1.27; 95% CI: 1.09, 1.48, P = 0.002) and women (PR = 1.21; 95% CI: 1.07, 1.37, P = 0.003) even after adjustment for age, lifestyle factors, serum levels of free triiodothyronine (FT3), and free thyroxine (FT4). Most of the components of MetS were common in higher serum TSH levels within the normal range.

CONCLUSION

The prevalence of MetS and most of its components increased in the higher TSH group in euthyroid Chinese population.

Thyroid disease and the metabolic syndrome

PURPOSE OF REVIEW

To summarize recent developments in the association of thyroid function with metabolic syndrome (MetS).

RECENT FINDINGS

Although thyroid hormones even within low normal range are associated with various metabolic abnormalities, the risk of MetS remains a controversial issue. Hyperthyroid state might be associated only with insulin resistance and dysglycemia. Autoimmune thyroid diseases may be a potential risk factor for metabolic abnormalities even in those with low normal thyroid function.

SUMMARY

The interrelation between thyroid stimulating hormone, free T3, freeT4 and metabolic parameters is complex and might be affected by age, sex, BMI, insulin resistance, smoking, iodine intake and inflammatory markers.

Association between serum thyrotropin within the euthyroid range and obesity

The relationship between variations in thyroid function and indices of obesity remains a focus of debate. To explore the associations between thyroid function within the normal range and obesity and to evaluate potential modifying factors, we analyzed a large and well-characterized community cohort in Beijing, China, containing 1,816 men and 1,774 women with serum thyrotropin (TSH) levels within the reference range (0.55-4.78 μIU/mL). Associations between TSH levels and BMI were identified using correlation analysis, ANOVA and Chi-square tests. Logistic regression analyses were used to estimate the impact of serum TSH on obesity before and after adjustment for possible confounding factors. The mean serum TSH was 2.04 ± 0.94 μIU/mL. TSH within the reference range was positively associated with BMI in both genders. Compared with euthyroid adults whose TSH was in the middle quartiles (TSH 1.30-2.60 μIU/mL) of the reference range, the odds of obesity (BMI ≥ 28.0 kg/m²) and severe obesity (BMI ≥ 33.0 kg/m²) was 38% (OR = 1.38, 95% CI 1.17-1.64) and 58% (OR = 1.58, 95% CI 1.12-2.21) more likely, respectively, among those with TSH in the upper quartile. For women, postmenopausal subjects with lower TSH levels had a lower risk of severe obesity (OR = 0.42, 95% CI 0.20-0.91) than those in the middle TSH quartile. Positive associations were found between serum TSH within the euthyroid range and obesity, and menopause showed a significant influence on the relationship between TSH level and severe obesity.

Thyroid function is associated with body mass index and fasting plasma glucose in Thai euthyroid population

AIMS

Several population-based studies found the associations between body mass index and thyroid function within the normal range. Furthermore, these thyroid functions are related with insulin resistance and plasma glucose levels. This study aimed to investigate the associations between thyroid functions and metabolic parameters in Thai euthyroid population.

METHODS

Participants from the Thai National Thai Health Examination Survey were randomly measured for TSH, FT4, anti-thyroperoxidase, and anti-thyroglobulin. Euthyroidism was defined by TSH 0.27-4.20 mIU/L and FT4 0.93-1.71 ng/dL.

RESULTS

A total of 2242 euthyroid participants were included. Fifty-one percent were female. Mean age, fasting plasma glucose, and body mass index were 55 ± 21 years, 93 ± 29 mg/dL, and 23.4 ± 4.6 kg/m², respectively. Multivariate regression analysis after age and sex adjustment showed a negative association of serum FT4 with body mass index (β = -0.070, p = 0.001) and the relationship was still significant after subjects with positive anti-thyroperoxidase were excluded (β = -0.068, p = 0.003). In contrast, serum TSH was positively associated with body mass index (β = 0.052, p = 0.012). Moreover, serum FT4 was positively associated with fasting plasma glucose levels (β = 0.097, p < 0.001).

CONCLUSIONS

Small variations of serum TSH and FT4 within the reference range may contribute to the differences in metabolic indexes such as body mass index and fasting plasma glucose.

Association between serum TSH levels and metabolic components in euthyroid subjects: a nationwide population-based study

BACKGROUND

Whether a relationship exists between various metabolic factors and thyroid-stimulating hormone (TSH) levels in euthyroid persons remains unknown. This study aims to explore the relationship between TSH levels and metabolic factors in euthyroid individuals.

METHODS

A total of 2,663 subjects were enrolled from a nationwide population-based cross-sectional survey of iodine nutrition, thyroid disease and diabetes in China (2014-2017). Euthyroid individuals were divided into four groups according to quartiles of TSH levels: group A (n=305, 0.3-1.3 mIU/L), group B (n=829, 1.3-2.2 mIU/L), group C (n=673, 2.2-3.2 mIU/L) and group D (n=349, 3.2-4.2 mIU/L). Anthropometric parameters, biochemical indicators and TSH levels were determined.

RESULTS

A total of 2,156 euthyroid subjects with serum TSH levels within the normal range accounted for 86.8% of the sample. The systolic blood pressure (SBP) in group D was significantly higher than that in the other three groups. Group C displayed significantly lower thyroid peroxidase antibody (TPOAb) levels than the other three groups. Group C also had lower anti-thyroglobulin antibody (TgAb) levels than groups A and D, whereas the TgAb levels in group B were only lower than those in group A. Spearman's or Pearson's linear regression analysis showed that SBP (r=0.054; P=0.013) was positively correlated with TSH, but cholesterol (TC) (r=-0.043, P=0.047) was negatively correlated with TSH. Multiple stepwise regression analysis revealed that SBP, the urinary iodine concentration (UIC), waist circumference (WC), body mass index (BMI), TC, triglycerides (TGs) and low-density lipoprotein cholesterol (LDL-C) were independent predictors of serum TSH levels.

CONCLUSION

This large population-based study demonstrates a significant interaction between metabolic factors and TSH levels. An adverse weight status, high blood pressure levels, blood lipid metabolism disorder and excessive iodine intake may be early manifestations of thyroid disease in euthyroid subjects.

Age and Gender Specific Thyroid Hormones and Their Relationships with Body Mass Index in a Large Chinese Population

OBJECTIVES

To investigate the associations of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4) with body mass index (BMI) and the effect of age and gender on these relationships in a large Chinese population.

METHODS

A total of 97,997 individuals from a health examination center were selected. The medians (25th and 75th) of TSH, FT3 and FT4 were used to explore the trends based on gender, 10-year age groups and BMI. The relationships of TSH, FT3 and FT4 with BMI were assessed by generalized additive models (GAM) along with adjusting the effect of age and gender.

RESULTS

After applying our exclusion criteria, 77,991 euthyroid participants (45,428 males and 32,563 females) were analyzed. The medians of TSH level based on BMI groups were significantly higher in female participants than those in males in all age groups (P < 0.05), and the median FT3 level was lower in female subjects; however, there was no significant difference between male and female subjects in median FT4 level. The GAM analysis showed the non-linear positive association of TSH and FT3 with BMI, and these relationships were markedly influenced by age and gender. However, FT4 had a negative relationship with BMI, with neglectable effect of age and gender.

CONCLUSIONS

TSH, FT3 and BMI have a non-linear and positive quadratic relationship after age and gender adjustment. FT4, however, has a negative non-linear relationship with BMI with neglectable influence of age and gender.

Waist Circumference and Subclinical Thyroid Dysfunction in a Large Cohort of Chinese Men and Women

OBJECTIVE

The association between subclinical thyroid dysfunction and waist circumference (WC) is still controversial, especially from the perspective of sex differences. We aimed to explore the impact of sex on this relationship in a large Chinese cohort.

METHODS

This cross-sectional study recruited 13,505 healthy participants (8,346 males, 5,159 females) who were enrolled in a health check program. Clinical data were collected. The association between subclinical thyroid dysfunction and WC of both sexes was analyzed separately after dividing WC into quartiles. Odds ratios (ORs) were calculated by binary logistic regression models, and linear regression analysis was also performed.

RESULTS

The prevalence rates of subclinical hyper-and hypothyroidism were significantly lower in males. Binary logistic regression models showed that WC in females with subclinical hypothyroidism had a detrimental effect with an OR of 1.011, but the effect disappeared when we included other covariates. The other ORs indicated no significant effects. The weak negative relationship between WC and thyrotropin was also indicated by linear regression analyses with very low R² values.

CONCLUSION

The current research did not show WC as a risk factor for subclinical thyroid dysfunction in either sex. Regional and ancestral origin differences may account for the variations with other studies.

ABBREVIATIONS

ALT = alanine aminotransferase; BMI = body mass index; FT3 = free triiodothyronine; FT4 = free thyroxine; TG = triglycerides; TSH = thyroid-stimulating hormone; UA = uric acid; WC = waist circumference.

Association between Thyroid Function and Body Mass Index: A 10-Year Follow-Up

BACKGROUND/AIMS

We aimed to evaluate the association between change in thyroid function tests within the euthyroid range and body mass index (BMI) in persons with normal weight at baseline.

METHODS

This study investigated 1,100 normal-weight euthyroid persons in a population-based cohort study, Tehran Thyroid Study. BMI was calculated and serum concentrations of thyrotropin (TSH) and free T4 (FT4) were assayed at baseline and after 10 years of follow-up. We evaluated the relationship between thyroid and obesity based on 2 definitions for outcome: (1) a binary outcome as BMI <25 or ≥25 kg/m2, and (2) a multinomial outcome as normal BMI, overweight, and obese.

RESULTS

A total of 569 women and 531 men, aged 36.3 ± 13.5 years, were included. Modified Poisson regression analysis for binary outcome, after adjustment for age, sex, smoking, and anti-thyroid peroxidase antibody status, revealed a negative association between delta serum FT4 and follow-up BMI (relative risk 0.55 [95% CI 0.37-0.80]) without any significant association between change in serum TSH and follow-up BMI. However, in multinomial logistic regression analysis, we found no relationship between delta serum FT4 or TSH and follow-up BMI categories, for either overweight or obese vs. normal-weight participants.

CONCLUSIONS

In normal-weight euthyroid individuals, changes in serum concentrations of FT4, but not TSH, may contribute to change in body weight.

Relationship between Body Mass Index, Waist-to-Hip Ratio, and Serum Lipid Concentrations and Thyroid-Stimulating Hormone in the Euthyroid Adult Population

The aim of this cross-sectional study was to investigate the relationship between body mass index (BMI), waist-to-hip ratio, and lipid parameters and serum thyroid-stimulating hormone (TSH) levels in healthy euthyroid individuals. This cross-sectional study was conducted between June 1^st and July 20^th, 2013, at Bushehr University of Medical Sciences. One hundred forty euthyroid individuals were divided into 2 groups: a high-TSH group (TSH between 2.0 and 5.5 mIU/L, n=67) and a low-TSH group (TSH between 0.3 and 2.0 mIU/L, n=73). After overnight fast, total cholesterol, triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), TSH, thyroxine (T4), and triiodothyronine (T3) were measured. Height and weight were measured with a stadiometer, and BMI was calculated as weight in kilograms divided by the square of height in meters. Waist-to-hip ratio was determined as waist circumference divided by hip circumference. The simple independent t-test and a general linear model were used for statistical analysis. All statistical analyses were done using the SPSS, version 15, statistical software package. BMI and LDL-C were significantly higher in the high-TSH group than in the low-TSH group after adjustment for age, sex, calorie intake, total fat and carbohydrate intakes, and physical activity. No significant differences were found between the groups in TG, cholesterol, and HDL-C. The association between TSH levels andT4 was significant. Individuals with TSH levels at the upper limit of normality might be at risk of hypercholesterolemia and obesity.

Association between Serum Thyroid-Stimulating Hormone Levels and Visceral Adipose Tissue: A Population-Based Study in Northeast Germany

BACKGROUND

Abdominal obesity is a major driver for adverse medical conditions. While an interaction between adipose tissue and thyroid function is thought to exist, to our knowledge, no study has examined the effect of thyroid-stimulating hormone (TSH) on visceral adipose tissue (VAT) in a population-based context.

OBJECTIVE

We determined an association between serum TSH levels and VAT.

METHODS

A sample of 1,021 female and 956 male adults aged 20-79 years was drawn from registry offices in the cross-sectional, population-based Study of Health in Pomerania Trend (SHIP Trend) in Northeast Germany from 2008 to 2012. Our main exposure was serum TSH levels. Our main outcome was VAT measured using magnetic resonance imaging. The possibly mediating role of leptin on the TSH-VAT association was also assessed.

RESULTS

A total of 1,719 participants (87.9%) had serum TSH levels within the reference range. The mean volume of VAT was 5.33 liters for men and 2.83 liters for women. No association between TSH and VAT (β = 0.06, 95% CI: -0.02, 0.14) was observed, and there were no differences detected between sexes. VAT was strongly associated with leptin with a greater effect in women than in men. Leptin was strongly associated with TSH.

CONCLUSIONS

No association between TSH and VAT was observed. Other biomarkers such as leptin may play a role in the relationship between thyroid function and metabolic risk.

The relation between changes in thyroid function and anthropometric indices during long-term follow-up of euthyroid subjects: the Tehran Thyroid Study (TTS)

OBJECTIVE

Uncertainties exist regarding the causal relationship between thyroid function tests (TFT) within the euthyroid range and anthropometric measures. This longitudinal cohort is aimed to examine the relationship between the two conditions.

SUBJECTS AND METHODS

Euthyroid participants of Tehran Thyroid Study (TTS) attending phase I (1999-2001) were included in this study and were followed up to phase IV (2008-2011). TSH and free T4 (fT4) levels as well as weight (Wt), waist circumference (WC), hip circumference (HC) and waist-to-hip ratio (WHR) were measured at both phases.

RESULTS

971 women and 784 men were included in the analysis. During 9.7years of follow-up, increases in TSH levels, Wt and WHR as well as a decrease in fT4 level were observed. Multivariable regression analysis showed a significant relationship between TSH changes and alterations in WC in women (β=0.69, P=0.021) and men (β=0.61, P=0.038). Moreover, a significant negative association of ΔfT4 with changes in weight was documented (β=-0.49, P=0.001 in women and β=-0.56, P<0.001 in men). Additionally, we found a negative relationship between ΔfT4 and ΔHC in men (β=-0.36, P=0.001).

CONCLUSION

In both genders, there was a positive relationship between changes in TSH and waist circumference and conversely a negative association of changes of fT4 levels with weight over time.

Carriers of a VEGFA enhancer polymorphism selectively binding CHOP/DDIT3 are predisposed to increased circulating levels of thyroid-stimulating hormone

BACKGROUND

Levels of serum thyroid-stimulating hormone (TSH) indicate thyroid function, because thyroid hormone negatively controls TSH release. Genetic variants in the vascular endothelial growth factor A (VEGFA) gene are associated with TSH levels. The aim of this study was to characterise the association of VEGFA variants with TSH in a Danish cohort and to identify and characterise functional variants.

METHODS

We performed an association study of the VEGFA locus for circulating TSH levels in 8445 Danish individuals. Lead variants were tested for allele-specific effects in vitro using luciferase reporter and gel-shift assays.

RESULTS

Four SNPs in VEGFA were associated with circulating TSH (rs9472138, rs881858, rs943080 and rs4711751). For rs881858, the presence of each G-allele was associated with a corresponding decrease in TSH levels of 2.3% (p=8.4×10^-9) and an increase in circulating free T4 levels (p=0.0014). The SNP rs881858 is located in a binding site for CHOP (C/EBP homology protein) and c/EBPβ (ccaat enhancer binding protein β). Reporter-gene analysis showed increased basal enhancer activity of the rs881858 A-allele versus the G-allele (34.5±9.9% (average±SEM), p=0.0012), while co-expression of CHOP effectively suppressed the rs881858 A-allele activity. The A-allele showed stronger binding to CHOP in gel-shift assays.

CONCLUSIONS

VEGF is an important angiogenic signal required for tissue expansion. We show that VEGFA variation giving allele-specific response to transcription factors with overlapping binding sites associate closely with circulating TSH levels. Because CHOP is induced by several types of intracellular stress, this indicates that cellular stress could be involved in the normal or pathophysiological response of the thyroid to TSH.

TRIAL REGISTRATION NUMBER

NCT00289237, NCT00316667; Results.