Relationship between pituitary-thyroid axis hormones and anthropometric parameters in Czech adult population

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.

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.

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 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.

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

OBJECTIVE

This cross-sectional study investigated the associations between the serum thyroid-stimulating hormone (TSH) concentration and indices of obesity in middle-aged Japanese men and women.

METHODS

The participants were 2,037 employees (1,044 men and 993 women; age, 36-55 yr) of a metal products factory in Japan. Clinical examinations were conducted in 2009. We obtained a medical history and anthropometric measurements (body weight, body mass index [BMI] and waist circumference) and measured the serum TSH concentrations. The anthropometric indices were compared across serum TSH quartiles. The associations were evaluated separately according to the smoking status in men.

RESULTS

The mean body weight (kg), BMI (kg/m(2)) and waist circumference (cm) were 69.2, 23.7 and 83.2 in men and 55.3, 22.3 and 74.3 in women, respectively. Men with a higher TSH concentration had higher body weight and BMI values (p for trend=0.016 and 0.019, respectively), and these significant associations were observed even after adjusting for age, smoking status and other potential confounders. The TSH level was not associated with waist circumference. We found a significant interaction between the TSH level and the smoking status on body weight (p for interaction=0.013) and a significant association between the TSH level and body weight in nonsmokers, but not in current smokers. No significant associations were observed between the TSH level and the anthropometric indices in women.

CONCLUSION

Significant positive associations between the serum TSH concentration, body weight and BMI were detected in men only, and an interaction with the smoking status was observed for this association.

Low-normal or high-normal thyrotropin target levels during treatment of hypothyroidism: a prospective, comparative study

BACKGROUND

Recent literature advocates the decrease of the upper limit of the normal thyrotropin (TSH) reference range. The objective of this study was to determine whether treated hypothyroid patients maintained within a low-normal TSH range (0.4-2.0 mIU/L) have better clinical outcomes than those maintained within a high-normal TSH range (2.0-4.0 mIU/L).

METHODS

The study was performed in a thyroid outpatient clinic of a tertiary hospital. This was a prospective, interventional study. Forty-two participants with newly diagnosed overt primary hypothyroidism were paired in two groups: group 1 (n=20), low-normal target TSH; group 2 (n = 22), high-normal target TSH. Levothyroxine was initiated, and dose was adjusted to achieve and sustain the target TSH value during the study period. After the target TSH was reached, participants were evaluated every 3 months for thyroid function, serum lipid profile, resting energy expenditure (REE), body composition, and bone mineral density, for 12 months.

RESULTS

Nineteen patients in group 1 and 16 in group 2 completed the study. In the whole-group analysis, total cholesterol (p = 0.01), low-density lipoprotein cholesterol (p = 0.004), and triglycerides (p < 0.001) decreased after treatment, whereas REE per kilogram of lean body mass (p = 0.001) and total fat body mass (p =0.02) increased. Group 1 patients had a significantly higher relative increase in REE (+7.1% ± 11.3% vs. +3.6% ± 15.1%, p = 0.02). There was no difference between the groups in the other variables.

CONCLUSIONS

Despite recent trends toward lowering the upper limit of normal TSH range, the results of this 12-month study provided no substantial clinical evidence to corroborate that treatment of primary hypothyroidism should aim at maintaining TSH levels in a low-normal range

Relationship between urinary metabolites of polycyclic aromatic hydrocarbons and thyroid hormone levels in Chinese non-occupational exposure adult males

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous global pollutants. Limited studies suggested that PAH may interfere with thyroid function in animals, but little is known about humans. A population of 480 Chinese males was recruited. Using LC-MS/MS, four urinary metabolites of PAH including 1-hydroxynaphthalene (1-N), 2-hydroxynaphthalene (2-N), 1-hydroxypyrene (1-P) and 2-hydroxyfluorene (2-F) were measured in spot urinary samples, which were adjusted by urinary creatinine (CR). Blood samples were collected for measuring serum levels of thyroid hormones including total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH). The median CR-adjusted urine PAH concentrations of 1-N, 2-N, 1-P, 2-F were 2.306, 4.047, 1.155 and 2.899 microg g(-1) of CR, respectively. Significant p-values for trend were found for men with higher 2-F tertiles and were more likely to possess high-reference TSH levels. In addition, the multivariate linear regression models showed significant positive correlations for TSH levels with increased CR-adjusted 2-F concentration. No significant associations were found between other thyroid hormones levels and PAH metabolite concentrations. These results indicated that PAH exposure might be related to altered male thyroid hormone levels, but further study is needed to confirm these observed findings.