Free Thyroxine Levels are Associated with Cold Induced Thermogenesis in Healthy Euthyroid Individuals

Temperature Differences Between Controlled Primary Hypothyroidism and Healthy Patients: An Exploratory Study

Introduction

Hypothyroidism is conventionally treated with replacement therapy through levothyroxine (LT4). Despite the improvement in symptoms, cold intolerance persists in some patients. The present study aims to determine whether there is a difference in temperature perception and skin temperature between patients with primary controlled hypothyroidism (PCH) and a group of healthy controls matched for body mass index and age. Secondarily we aimed to determine difference in quality of life.

Methodology

Skin temperature measurements were performed in both groups, both in the central and peripheral regions of the body. In addition, subjects were asked about their perception of temperature in a temperature-controlled room; anthropometric measurements were taken, their quality of life was assessed using the ThyPRO-39, and a thyroid hormone profile was performed.

Results

Eleven patients in the PCH group and 30 patients in the control group were studied. It was found that the group with PCH presented a significantly lower palmar temperature than the control group [mean (SD) of 32.05 (1.79) vs 33.10 (1.30) oC, P = .046]. A mediation model showed a direct effect. Temperature perception was equal between groups. The median (interquartile range) of ThyPRO was 8 (5.2) points in the control group vs 21.8 (13.5) in the group of controlled hypothyroidism, P < .001.

Discussion

These results suggest that, despite LT4 treatment, patients continue to present abnormalities in thermogenesis-related thermogenesis, and this may be due to a lack of hormonal adaptation to environmental changes and physiological demands, leading to lower body temperatures and increased sensitivity to cold.

18F-FDG PET/CT technology for the assessment of brown adipose tissue: an updated review

INTRODUCTION

This review provides an update of 18 F-fluorodeoxyglucose ([18F] FDG) for Brown adipose tissue (BAT) activity quantification, whose role is not completely understood.

AREAS COVERED

We conducted an unstructured search of the literature for any studies employing the [18F] FDG PET in BAT assessment. We explored BAT quantification both in healthy individuals and in different pathologies, after cold exposure and as a metabolic biomarker. The assessment of possible BAT modulators by using [18F] FDG PET is shown. Further PET tracers and novel developments for BAT assessments are also described.

EXPERT OPINION

Further PET tracers and imaging modalities are under investigation, but the [18F] FDG PET is currently the method of choice for the evaluation of BAT and further multicentric trials are needed for a better understanding of the BAT physiopathology, also after cold stimuli. The modulation of BAT activity, assessed by [18F] FDG PET imaging, seems a promising tool for the management of conditions such as obesity and type 2 diabetes. Moreover, an interesting possible correlation of BAT activation with prognostic [18F] FDG PET indices in cancer patients should be assessed with further multicentric trials.

Temporal trend and global burden of type 2 diabetes attributable to non-optimal temperature, 1990-2019: an analysis for the Global Burden of Disease Study 2019

Exposure to hot or cold temperatures was reported to be associated with increased mortality and morbidity of type 2 diabetes, but few studies have estimated the temporal trend and global burden of type 2 diabetes attributable to non-optimal temperature. Based on the Global Burden of Disease Study 2019, we collected data on the numbers and rates of deaths and disability-adjusted life years (DALYs) of type 2 diabetes attributed to non-optimal temperature. The joinpoint regression analysis was used to estimate the temporal trends of the age-standardized rate of mortality and DALYs from 1990 to 2019 by average annual percentage change (AAPC). From 1990 to 2019, globally, the numbers of deaths and DALYs of type 2 diabetes attributable to non-optimal temperature increased by 136.13% (95% (uncertainty interval) UI: 87.04% to 277.76%) and 122.26% (95% UI: 68.77% to 275.59%), with the number from 0.05 (95% UI: 0.02 to 0.07) million and 0.96 (95% UI: 0.37 to 1.51) million in 1990 to 0. 11 (95% UI: 0.07 to 0.15) million and 2.14 (95% UI: 1.35 to 3.13) million in 2019. The age-standardized mortality rate (ASMR) and DALYs rate (ASDR) of type 2 diabetes attributable to non-optimal temperature showed an increasing trend in the high temperature effect and lower (low, low-middle and middle) socio-demographic index (SDI) region, with AAPCs of 3.17%, 1.24%, 1.61%, and 0.79% (all P < 0.05), respectively. The greatest increased ASMR and ASDR were observed in Central Asia, followed by Western Sub-Saharan Africa and South Asia. Meanwhile, the contribution of type 2 diabetes burden attributable to high temperature gradually increased globally and in five SDI regions. In addition, the global age-specific rate of mortality and DALYs of type 2 diabetes attributable to non-optimal temperature for both men and women almost increased with age in 2019. The global burden of type 2 diabetes attributable to non-optimal temperature increased from 1990 to 2019, particularly in high temperature, regions with lower SDI, and the older population. Appropriate temperature interventions are necessary to curb climate change and increasing diabetes.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

The Role of Thyroid Hormones on Skeletal Muscle Thermogenesis

Nowadays obesity becomes a significant global problem. Hence, recently more and more attention has been paid to substances present in the body that have a significant impact on metabolic processes and thermogenesis, in the context of their potential use in the prevention and treatment of obesity. It is well known that the relationship between thyroid hormones and obesity is multilayered, however recently, more and more information about the possible relation between thyroid hormones and muscle metabolism has been published. The aim of this review is to present the most updated information on the physiological impact of thyroid hormones on muscle tissue, as well as pathological changes related to the occurrence of various types of thyroid disorders, including hypothyroidism, hyperthyroidism and sick euthyroid syndrome. However, the data in humans still remains insufficient, and further studies are needed to fully explore the thyroid-muscle cross-talk.

Obesity and Thyroid Axis

Development of obesity is primarily the result of imbalance between energy intake and energy expenditure. Thyroid hormones influence energy expenditure by regulating cellular respiration and thermogenesis and by determining resting metabolic rate. Triiodothyronine influences lipid turnover in adipocytes and impacts appetite regulation through the central nervous system, mainly the hypothalamus. Thyroid-stimulating hormone may also influence thermogenesis, suppress appetite and regulate lipid storage through lipolysis and lipogenesis control. Subclinical hypothyroidism may induce changes in basal metabolic rate with subsequent increase in BMI, but obesity can also affect thyroid function via several mechanisms such as lipotoxicity and changes in adipokines and inflammatory cytokine secretion. The present study investigated the complex and mutual relationships between the thyroid axis and adiposity.