Resting energy expenditure is sensitive to small dose changes in patients on chronic thyroid hormone replacement

What could be the reasons for not losing weight even after following a weight loss program?

INTRODUCTION

Approximately four million people worldwide die annually because of obesity. Weight loss is commonly recommended as a first-line therapy in overweight and obese patients. Although many individuals attempt to lose weight, not everyone achieves optimal success. Few studies point out that weight loss eventually slows down, stagnates or reverses in 85% of the cases.

RESEARCH QUESTION

What could be the reasons for not losing weight even after following a weight loss program?

METHODS

A scoping review of the literature was performed using weight loss-related search terms such as 'Obesity,' 'Overweight,' 'Lifestyle,' 'weight loss,' 'Basal Metabolism,' 'physical activity,' 'adherence,' 'energy balance,' 'Sleep' and 'adaptations. The search involved reference tracking and database and web searches (PUBMED, Science Direct, Elsevier, Web of Science and Google Scholar). Original articles and review papers on weight loss involving human participants and adults aged > 18 years were selected. Approximately 231 articles were reviewed, and 185 were included based on the inclusion criteria.

DESIGN

Scoping review.

RESULTS

In this review, the factors associated with not losing weight have broadly been divided into five categories. Studies highlighting each subfactor were critically reviewed and discussed. A wide degree of interindividual variability in weight loss is common in studies even after controlling for variables such as adherence, sex, physical activity and baseline weight. In addition to these variables, variations in factors such as previous weight loss attempts, sleep habits, meal timings and medications can play a crucial role in upregulating or downregulating the association between energy deficit and weight loss results.

CONCLUSION

This review identifies and clarifies the role of several factors that may hinder weight loss after the exploration of existing evidence. Judging the effectiveness of respective lifestyle interventions by simply observing the 'general behavior of the groups' is not always applicable in clinical practice. Each individual must be monitored and advised as per their requirements and challenges.

A Cross-Sectional Study Examining the Parametric Thyroid Feedback Quantile Index and Its Relationship with Metabolic and Cardiovascular Diseases

Background: The usual inverse correlation between thyrotropin (TSH) and thyroid hormone disappears in syndromes of central resistance to thyroid hormone, where both are high. TSH and thyroid hormone are also simultaneously high when there is an elevation of the set point of the thyroid regulation axis. This can be estimated with indices, such as the Parametric Thyroid Feedback Quantile-based Index (PTFQI), which was designed for the general population. The PTFQI is positively associated with diabetes prevalence, but association with other pathologies has not been yet explored. The aim of this project was to explore the potential relationship of the PTFQI with metabolic and cardiovascular disease in a sample of ambulatory adult patients from Spain. Methods: A cross-sectional study was carried out among the patients who underwent thyroid hormones measurement (6434 measurements from September to November 2018 in a central laboratory in Spain). We retrospectively reviewed clinical records of a subgroup of adults aged >18 years with normal TSH and free thyroxine (fT4) belonging to groups that represent extreme PTFQI (n = 661). Individuals with known conditions interfering the thyroid axis were excluded (remaining n = 296). Logistic and linear regression models adjusted for age and sex were used to calculate odds ratio (OR) of diseases and differences of clinical parameters, and 95% confidence intervals [CI]. Results: Across levels with higher PTFQI, there was an increase in the prevalence of type 2 diabetes (High vs. Low PTFQI OR: 2.88 [CI: 1.14-7.86], p-Trend = 0.02), ischemic heart disease (16.4% vs. 0%, unadjusted Haldane-Anscombe corrected OR: 23.90 [CI: 1.36-21.48], adjusted p-Trend = 0.04), atrial fibrillation (OR: 8.13 [CI: 1.33-158.20], p-Trend = 0.05), and hypertension (OR: 3.19 [CI: 1.14-9.94], p-Trend = 0.05). While the prevalence of type 2 diabetes was similarly associated with TSH and fT4, ischemic heart disease, atrial fibrillation, and hypertension were more strongly associated with the differences in fT4 values. Conclusions: Type 2 diabetes, ischemic heart disease, atrial fibrillation, and hypertension may be associated with a higher central regulation set point for thyroid hormone. These findings should be confirmed in other populations.

The Impact of the Metabolic Syndrome and Its Components on Resting Energy Expenditure

We determined whether metabolic syndrome (MetS) and the increasing number of its components influenced the resting energy expenditure (REE). Data on adult men (n = 72, 40%) and women (n = 108, 60%) from European (n = 154, 86%) and Sub-Saharan African (n = 26, 14%) ancestry were used. Ninety-five (53%) participants had MetS (MetS+), while 85 (47%) were without MetS (MetS−). REE was determined through indirect calorimetry, body composition by DEXA, and clinical biochemistry by standard laboratory techniques. MetS+ had a significantly higher REE (mean ± se: MetS+: 5995 ± 87.3 vs. MetS−: 5760 ± 86.3 kJ/d, p = 0.025) when adjusted for age, gender, fat mass (FM), fat-free mass (FFM), ethnicity, season, 25OHD, insulin sensitivity, and time of data collection. Within each MetS status group, an increase in the number of components (C) resulted in a stepwise increase in REE. Relative to zero components, those with 1C had adjusted REE higher by +526 ± 248.1 kJ/d (p = 0.037), while 2C were higher than 1C by +298 ± 140.8 kJ/d (p = 0.037). Similarly, relative to 3C, those with 4C had REE higher by +242 ± 120.7 kJ/d (p = 0.049). The higher REE of 5C over 4C by 132 ± 174.5 kJ/d did not achieve statistical significance. MetS was associated with a significantly higher REE. This greater energetic cost varied directly with the numbers of its components but was most evident in those not diagnosed with the syndrome.

Association between thyroid hormone and components of metabolic syndrome in euthyroid Korean adults: A population-based study

Thyroid dysfunction increases the prevalence of metabolic syndrome. However, the link between thyroid hormones and metabolic syndrome remains debatable, and the effect of sex on their relationship is not completely understood. To elucidate the relationship of thyroid hormones with metabolic syndrome and its components according to sex in euthyroid individuals in South Korea. Adult participants who underwent thyroid tests at our institution between January 2015 and December 2018 and had thyroid-stimulating hormone (TSH; 0.270-4.200 μIU/mL) and free thyroxine (FT4; 0.93-1.70 ng/dL) levels in the normal range were included. After correcting for age and body mass index, multiple linear regression was performed to assess the association of TSH and FT4 with metabolic syndrome and its components, and logistic regression was performed to estimate the risk of developing metabolic syndrome and its components according to different thyroid hormone quartiles. We included 12,478 men and 7,575 women in this study. The prevalence of metabolic syndrome was 9.68%. In men, TSH was positively associated with blood pressure and triglycerides, and the odds ratio for high blood pressure and hypertriglyceridemia was approximately 1.3 times higher in the fourth quartile than in the first quartile. FT4 associated positively with waist circumference, and a high odds ratio for abdominal obesity in the fourth quartile was observed in both men (odds ratio [OR], 1.239; 95% confidence interval [CI], 1.045-1.470) and women (OR, 1.302; 95% CI, 1.029-1.649). A negative association was found between FT4 and triglycerides, and concurrently, the odds ratios for hypertriglyceridemia were lower in the fourth quartile in both men (OR, 0.692; 95% CI, 0.619-0.774) and women (OR: 0.641; 95% CI: 0.512-0.803). In addition, a higher odds ratio for high blood pressure was observed in the fourth quartiles of FT4 and TSH in women. However, there was no association between TSH and FT4 levels and the onset of metabolic syndrome in either of the sexes. Serum TSH and FT4 levels were associated with different metabolic syndrome components in men and women, but there was no association with the onset of metabolic syndrome.

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.

Patterns of Bodyweight Changes in Patients With Hypothyroidism, a Retrospective Study From Basrah, Southern Iraq

Background

Weight gain is one of the most important hypothyroidism-related concerns in patients with hypothyroidism. However, unexpectedly, levothyroxine replacement does not necessarily result in body weight (BWT) reduction among those patients. The study aimed to assess the patterns of BWT changes through time in patients with hypothyroidism.

Method

In a retrospective database study from Faiha Specialized Diabetes, Endocrine, and Metabolism Center, a total of 346 adult patients with hypothyroidism (192 newly diagnosed and 154 known hypothyroidism patients) who had one visit every three months, five visits in one year were included. Of these, 116 new and 69 known hypothyroidism patients had completed nine visits in two years. Each visit involved thyroid-stimulating hormone (TSH) and BWT measurements. Patients with chronic liver or renal disease, diabetes mellitus, thyroid cancer, or other malignancies, pregnancy, and steroid or hormonal therapies were excluded. The patients were further subdivided based on average TSH levels into controlled (TSH ≤ 4.2 μIU/ml) and uncontrolled (TSH > 4.2 μIU/ml). Repeated measures analysis of variance (ANOVA) with a Greenhouse-Geisser correction and post hoc tests using the Bonferroni correction were used to evaluate TSH and BWT changes through the study.

Results

Both in newly diagnosed and known hypothyroidism patients with an average TSH > 4.2 μIU/mL, BWT increased significantly through visits over one and two years. For newly diagnosed patients assessed over one year (F(2.41, 321.60) = 3.28, p = 0.03), the mean BWT increase was 1.4 ± 0.38 kg from 3rd to 12th month visits (p = 0.004). For newly diagnosed patients assessed over two years (F(3.10, 263.89) = 9.08, P < 0.0005), the mean BWT increase was 3.02 ± 0.77 kg from 3rd to 24th month visits (p = 0.007). For patients with known hypothyroidism assessed over one year (F(2.56, 187.47) = 7.11, p = 0.0003), the mean BWT increase was 1.97 ± 0.64 kg at 12th month visit, and over two years (F(2.35, 77.56) = 4.67, P = 0.009), the mean BWT increase was 3.78 ± 1.26 kg at 24th month visit. While in all other patients with an average TSH ≤ 4.2 μIU/mL, the BWT changed non-significantly through the visits for newly diagnosed patients over one year and two years (p = 0.10, 0.34, respectively), and known patients over one year and two years (p = 0.47, 0.34, respectively).

Conclusion

Contrary to what is believed, adequate treatment with levothyroxine does not associate with weight reduction. Instead, either the patient kept on the same weight or continued to gain more weight.

Common Electrolyte and Metabolic Abnormalities Among Thyroid Patients

The prevalence of thyroid diseases is high in the general population and causes serious abnormalities and disorders that can affect the quality of life. Many complications can result from poor or inappropriate management of the disease, leading to serious cardiovascular and metabolic complications. In the present review study, we aim to discuss the effect of thyroid diseases on metabolic and electrolyte abnormalities and the potential correlation with some common disorders. Evidence from previous studies has demonstrated that thyroid dysfunctions hugely affect the metabolism of glucose in the bodies of the affected patients, which can lead to the development of both type 1 and 2 diabetes mellitus (DM). Hyperthyroidism can lead to the development of impaired glucose tolerance and secondary diabetes mellitus. These include an increased glycogenolysis and gluconeogenesis process, increased intestinal absorption of glucose, and secondary ketogenesis and lipolysis, which will subsequently affect the functions of the insulin-secreting cells of the pancreas. Evidence showed that thyroid diseases are associated with the development of obesity and metabolic syndrome, and the management for these modalities should involve prior management of underlying thyroid diseases. Efforts should be made to adequately manage these cases with concomitant approaches to achieve the best clinical outcomes.

Association Between Body Mass Index and Thyroid Function in Euthyroid Chinese Adults

BACKGROUND Obesity can influence thyroid function through multiple routes, even in people who are euthyroid. The correlation between weight and thyroid function is a matter of debate. The present study investigated the relationship between body weight and thyroid function in euthyroid Chinese adults. MATERIAL AND METHODS A total of 1564 participants with serum thyrotropin (TSH) and thyroid hormone levels within the reference range were included. All of them were tested for thyroid function parameters and categorized, based on body mass index (BMI), into 3 groups: normal weight, overweight, and obese. The effects of BMI on thyroid function were examined using linear (continuous values) and logistic (dichotomous levels according to medians or means) regression and controlling for age and sex. RESULTS There were significant differences in free triiodothyronine (FT3) levels and FT3/free thyroxine (FT4) ratios among participants who were normal weight, overweight, and obese (both P<0.001). Multivariable regression analysis (P<0.001) showed that BMI was positively associated with FT3 levels and FT3/FT4 ratios. Compared with the normal weight group, the patients who were overweight or obese had significantly higher FT3 levels and FT3/FT4 ratios that were higher than average, according to logistic regression analyses. CONCLUSIONS We found that Chinese adults who are obese may have higher FT3 levels and FT3/FT4 ratios than those who are of normal weight, even if their thyroid function values are within the normal range.

Lower normal free thyroxine is associated with a higher risk of metabolic syndrome: a retrospective cohort on Chinese population

BACKGROUND

Recently, the relationship between thyroid hormones (THs) across the euthyroid ranges and metabolic syndrome (MetS) has been widely discussed. This study aimed to present specific cutoff values of THs to assess the association between THs and MetS in a euthyroid cohort.

METHODS

Data of 2694 subjects, aged 18-80 years, who attended health examination in Xi'an Electric Power Central Hospital from April 2011 to December 2015 were collected and analyzed. The first cohort enrolled 929 participants (followed up by 2221 person-years totally) to assess correlations between serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4) levels and MetS. The second cohort included 698 participants (followed up by 1709 person-years totally) to evaluate relationships between serum free triiodothyronine (FT3), free thyroxine (FT4) levels and MetS. MetS was defined according to the criteria of the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) scientific statements of 2009. Euthyroidism was defined as serum TSH, FT3 and FT4 levels within the reference ranges without taking any thyroid medication.

RESULTS

The cutoff values for TSH, T3, T4, FT3 and FT4 were 2.0mIU/L, 1.9 nmol/L, 117 nmol/L, 4.3 pmol/L and 16 pmol/L, respectively. Participants were categorized into two groups according to cutoff values: the lower-THs group and the higher-THs group. There was no significant difference in the risk of MetS between two groups in TSH, T3, T4 and FT3. The incidence of MetS was significantly higher in lower-FT4 group than higher-FT4 group (1.00 vs 0.622 (0.458, 0.846), P = 0.002). The lower-FT4/higher-TSH group had the highest hazard ratios of MetS. (2.131vs 1.0 (1.380,3.291), P = 0.006).

CONCLUSIONS

Lower normal FT4 (FT4 ≤ 16.0 pmol/L) is an independent risk factor for MetS, and lower normal thyroid function (TSH > 2.0 mIU/L and FT4 ≤ 16.0 pmol/L) is associated with a higher risk of developing MetS.

The Relationship Between Thyroid Function and Body Composition, Leptin, Adiponectin, and Insulin Sensitivity in Morbidly Obese Euthyroid Subjects Compared to Non-obese Subjects

Background/Objectives

Thyroid function tests (TFTs) changes in obese people have been studied with increasing interest, however, studies have been inconsistent hence it remains poorly understood. We compared the TFTs of morbidly obese euthyroid Saudi subjects with non-obese controls and then we examined the influence of leptin, adiponectin, and insulin resistance on TFTs.

Subjects/Methods

Fifty-five euthyroid obese subjects attending bariatric surgery clinic and 52 non-obese age-and gender-matched controls were recruited. We measured body weight, BMI, body composition, thyroid-stimulating hormone (TSH), Free T4 (FT4), Free T3(FT3), thyroid antibodies, fasting leptin, adiponectin, and lipid profile. Insulin resistance was quantified by HOMA-IR. Data are presented as mean ± SEM.

Results

Mean BMI was 45.6 ± 1.5 and 23.2 ± 0.5 kg/m², for the obese and non-obese controls, respectively, P value < 0.001. Mean TSH was 2.7 ± 0.18 mIU/L in obese subjects and 1.7 ± 0.13 mIU/L (0.27-4.2) in the non-obese controls, respectively, P value .014. Mean FT3 was 3.9 ± 0.1 pmol/L (3.1-6.8) in obese subjects compared to 5.0 ± 0.1 pmol/L in non-obese controls, respectively, P value 0.001, however, FT4 was similar in the 2 groups. In the whole group (N = 107), BMI correlated positively with TSH and negatively with FT3. Leptin correlated negatively with both FT4 and FT3 in the non-obese group only while none of the TFTs correlated with HOMA-IR or adiponectin in either group. Binary logistic regression showed that each 1 unit increase in TSH increased the odds of becoming obese by 12.7, P value 0.009, 95 C.I. (1.9-85.0). Conversely, each - unit increase in FT3 decreased the odds of becoming obese by 0.2, P value 0.023, 95% C.I. (0.05-0.80).

Conclusions

We report a small increase in TSH and a small decrease in FT3 within the normal range in obese subjects compared to non-obese controls. We also report a positive correlation between TSH and BMI with increased odds ratio of becoming obese with the increase in TSH and decrease in FT3. These changes may be either causally related or adaptive to the obesity state. FT4 and FT3 seem to correlate with leptin (but not with adiponectin or HOMA-IR) in the non-obese controls only. Larger mechanistic studies are needed to further elucidate the interesting association between obesity and TFTs.

Standard hypothyroid treatment did not restore proper metabolic response to carbohydrate

PURPOSE

Hypothyroidism is associated with a lower metabolic rate, impaired glucose tolerance, and increased responsiveness of sympathetic nervous system to glucose ingestion. The Levothyroxine (LT4) monotherapy is the standard treatment for hypothyroidism; however to what extent this treatment restores the patients' metabolism has not been verified. The aim of this study was to test the hypothesis that standard LT4 therapy may not restore proper metabolic response to carbohydrate ingestion.

METHODS

Energy expenditure, glucose tolerance, and catecholamine response to glucose ingestion were compared in 18 subjects with pharmacologically compensated hypothyroidism (PCH) and controls, at baseline and during oral glucose tolerance test conditions.

RESULTS

Metabolic rate was significantly lower in PCH (P < 0.0001). Glucose tolerance was decreased in this group with no differences in insulin resistance indicators between both groups. Adrenergic activity (P < 0.05) as well as adrenergic reaction to glucose ingestion (P < 0.001) were stronger in PCH.

CONCLUSIONS

Standard treatment for hypothyroidism does not restore the normal metabolic reaction to carbohydrate which is observed in healthy people.

A Feedforward Loop within the Thyroid-Brown Fat Axis Facilitates Thermoregulation

Thyroid hormones (TH) control brown adipose tissue (BAT) activation and differentiation, but their subsequent homeostatic response following BAT activation remains obscure. This study aimed to investigate the relationship between cold- and capsinoids-induced BAT activation and TH changes between baseline and 2 hours post-intervention. Nineteen healthy subjects underwent ¹⁸F-fluorodeoxyglucose positron-emission tomography (¹⁸F-FDG PET) and whole-body calorimetry (WBC) after 2 hours of cold exposure (~14.5 °C) or capsinoids ingestion (12 mg) in a crossover design. Standardized uptake values (SUV-mean) of the region of interest and energy expenditure (EE) were measured. Plasma free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) were measured before and 2 hours after each intervention. Subjects were divided into groups based on the presence (n = 12) or absence (n = 7) of BAT after cold exposure. 12 of 19 subjects were classified as BAT-positive. Subjects with BAT had higher baseline FT3 concentration, baseline FT3/FT4 ratio compared with subjects without BAT. Controlling for body fat percentage, FT3 concentration at baseline was associated with EE change from baseline after cold exposure (P = 0.037) and capsinoids (P = 0.047). Plasma FT4 level significantly increased associated with reciprocal decline in TSH after acute cold exposure and capsinoids independently of subject and treatment status. Circulating FT3 was higher in BAT-positive subjects and was a stronger predictor of EE changes after cold exposure and capsinoids in healthy humans. BAT activation elevates plasma FT4 acutely and may contribute towards augmentation of thermogenesis via a positive feedback response.

3-Iodothyronamine and Derivatives: New Allies Against Metabolic Syndrome?

In the two decades since its discovery, a large body of evidence has amassed to highlight the potential of 3-iodothyronamine (T1AM) as an antiobesity drug, whose pleiotropic signaling actions profoundly impact energy metabolism. In the present review, we recapitulate the most relevant properties of T1AM, including its structural and functional relationship to thyroid hormone, its endogenous levels, molecular targets, as well as its genomic and non-genomic effects on metabolism elicited in experimental models after exogenous administration. The physiological and pathophysiological relevance of T1AM in the regulation of energy homeostasis and metabolism is also discussed, along with its potential therapeutic applications in metabolic disturbances. Finally, we examine a number of T1AM analogs that have been recently developed with the aim of designing novel pharmacological agents for the treatment of interlinked diseases, such as metabolic and neurodegenerative disorders, as well as additional synthetic tools that can be exploited to further explore T1AM-dependent mechanisms and the physiological roles of trace amine-associated receptor 1 (TAAR1)-mediated effects.

Association of thyroid hormones with resting energy expenditure and complement C3 in normal weight high body fat women

BACKGROUND

A high body fat percentage has a specific effect on activation of the hypothalamic-pituitary-thyroid axis. On the other hand, a slight change in thyroid hormones can affect metabolism and body composition as well as immune function. This study aims to examine the relationship between adiposity, thyroid hormone levels and immunity by comparing resting energy expenditure (REE), serum thyroid hormone levels and complement C3 in normal-weight high body fat (normal weight obesity) women and normal-weight normal body fat women.

METHODS

In this case-control study, 40 women with normal body weight (BMI < 24.9 kg/m2) and body fat mass (FM) ≥ 30% (normal-weight obesity (NWO) group), and 30 non-obese women (BMI < 24.9 kg/m2) and FM < 30% (non-normal weight obesity (non-NWO) group) were recruited from a sport club in Tehran. Body composition was analyzed using bioimpedance analyzer. Blood samples were collected and analyzed for fasting serum concentration of thyroid hormones (including total T3 and total T4), thyroid-stimulating hormone (TSH), and serum complement C3. REE was measured by an indirect calorimetry.

RESULTS

Serum T3 and T4 and also complement C3 were higher in the NWO group than in the non-NWO group. Body fat percentages had significant positive correlation with T3 (r; 0.344, P <  0.05), T4 (r; 0.294, P <  0.05), and complement C3 (r; 0.417, P <  0.05). Serum T3 and T4 were also positively correlated with C3 concentration (r; 0.417, p <  0.001) and (r; 0.349, p <  0.05); respectively, but there was no significant correlation between TSH and C3. REE was not significantly different between the two groups. REE only had a significant positive correlation with fat-free mass (r; 0.421, P <  0.001).

CONCLUSION

An increase in body fat even in the presence of a normal body weight can be accompanied by the changes in thyroid function and inflammatory markers such as complement C3.

Effects of Short-Term Fasting and Different Overfeeding Diets on Thyroid Hormones in Healthy Humans

Background: A greater decrease in 24-hour energy expenditure (EE) during fasting and a smaller increase in 24-hour EE during low-protein overfeeding (metabolic "thrifty" phenotype) predict weight gain. As thyroid hormones (TH) are implicated in energy intake and metabolism, we assessed whether: (i) TH concentrations are altered by 24-hour fasting or overfeeding diets with varying protein content and (ii) diet-related changes in TH correlate with concomitant changes in EE. Methods: Fifty-eight euthyroid healthy subjects with normal glucose regulation underwent 24-hour dietary interventions including fasting, eucaloric feeding, and five overfeeding diets in a crossover design within a whole-room indirect calorimeter to measure the 24-hour EE. Overfeeding diets (200% of energy requirements) included three diets with 20% protein, one diet with 3% protein (low-protein overfeeding diet [LPF]: 46% fat), and one diet with 30% protein (high-protein overfeeding diet [HPF]: 44% fat, n = 51). Plasma free thyroxine (fT4), free triiodothyronine (fT3), and fibroblast growth factor 21 (FGF21) concentrations were measured after overnight fast the morning of and after each diet. Results: On average, fT4 increased by 8% (+0.10 ng/dL, 95% confidence interval [CI 0.07-0.13], p < 0.0001) and fT3 decreased by 6% (-0.17 pg/mL [CI -0.27 to -0.07], p = 0.001) after 24-hour fasting, whereas both fT4 and fT3 decreased by 5% (-0.07 ng/dL [CI -0.11 to -0.04], p < 0.0001) and 4% (-0.14 pg/mL [CI -0.24 to -0.04], p = 0.008) following HPF, respectively. Greater decreases in fT3 after HPF are associated with larger decreases in FGF21 (r = 0.40, p = 0.005). Following LPF, the mean fT3 increased by 6% (+0.14 pg/mL [CI 0.05-0.2], p = 0.003) with no change in fT4 (p = 0.7). No changes in TH were observed after normal-protein overfeeding diets (all p > 0.1). No associations were observed between TH concentrations and diet-related changes in 24-hour EE during any diet (all p > 0.07). Conclusions: Acute (200%) short-term (24 hours) changes in food intake induce small changes in TH concentrations only after diets with low (0% fasting and 3% protein overfeeding) or high (30% protein overfeeding) protein content. The fT3-FGF21 association after high-protein overfeeding suggests a role for TH in inhibiting FGF21 secretion by the liver during protein excess. These results indicate that TH are involved in protein metabolism; however, they do not mediate the short-term EE response to diets that characterize the metabolic phenotypes and determine the individual susceptibility to weight gain.

Body Composition, Resting Energy Expenditure, and Metabolic Changes in Women Diagnosed with Differentiated Thyroid Carcinoma

Background: Thyroid hormones heavily impact energy expenditure, body mass, and body composition. Their role in the state of exogenous subclinical hyperthyroidism in differentiated thyroid carcinoma (DTC) patients, however, is less well defined. The first aim of this study was to assess changes in body weight, body composition, resting energy expenditure (REE), respiratory quotient (RQ), and metabolic parameters in female DTC patients, starting from the phase of a euthyroid state before total thyroidectomy through the subsequent year after thyrotropin (TSH) suppression. The second aim was to assess the relationship between these variables and thyroid function parameters. Methods: This observational case series analyzed changes in body composition, calorimetric, and metabolic parameters of 15 DTC female patients at 5 time points: (1) at initial DTC diagnosis (euthyroid state), (2) at 2-3 weeks after thyroidectomy (hypothyroid state), (3) at 2-3 months of levothyroxine (LT4) treatment (exogenous euthyroid state), (4) after 6-9 months, and (5) after 1 year of TSH suppressive LT4 therapy (exogenous subclinical hyperthyroid state). A generalized estimating equation (GEE) analysis was performed to estimate the longitudinal correlations of the total triiodothyronine (TT3)/free thyroxine (fT4) ratio (as an independent variable) with body composition, metabolic, and calorimetric parameter changes (as dependent variables). Results: REE, REE per kilogram of lean body mass (REE/LBM), pulse, and systolic and diastolic blood pressure were significantly higher after TSH suppressive LT4 therapy. The GEE analysis revealed longitudinal negative correlations between the TT3/fT4 ratio and systolic blood pressure, fasting blood glucose, body mass index, android (abdominal wall and visceral mesentery) fat distribution, trunk, and arm fat distribution, REE, and REE/LBM. There was a positive correlation with RQ. Conclusions: REE, REE/LBM, pulse, and systolic and diastolic blood pressure were significantly higher after thyroidectomy, radioiodine and TSH suppressive therapy in female DTC patients, while no changes were observed in body weight or body composition. A lower TT3/fT4 ratio longitudinally correlated with increases in REE, REE/LBM, abdominal fat distribution, systolic blood pressure, and fasting blood glucose, as well as with decreased RQ. These findings highlight the importance of judicial balancing of the benefits and detriments of TSH suppression with subsequent decreased TT3/fT4 ratios for female DTC patients.

Thyroid function, body mass index, and metabolic risk markers in euthyroid adults: a cohort study

BACKGROUND

In recent years, the relationship between thyroid stimulating hormone (TSH) and obesity has been widely discussed. However, it is unclear how thyroid hormone concentrations relate to body weight and its impact on metabolic risk markers. This study aimed to assess how thyroid function is linked to underweight, overweight, or obesity, and metabolic risk markers in adults.

METHODS

A total of 16,975 subjects, aged 18-80 years, who attended the Health Management Center of Tongji Hospital, Wuhan, China were enrolled in this study. Anthropometric and laboratory data were collected and analyzed.

RESULTS

Serum free triiodothyronine (fT3) and fT3/free thyroxine (fT4) ratio (fT3/fT4) were positively associated with body mass index (BMI) (P < 0.001), while there was a negative relationship between fT4 and BMI (P < 0.001) according to multivariable regression analysis adjusted for age and sex. Associations between thyroid hormone concentrations and markers of blood pressure, and lipid and glucose metabolism were identified after adjustment for age, sex, and BMI, with TSH being negatively associated with fasting blood glucose (FBG). fT3 was positively associated with systolic blood pressure and low-density lipoprotein-cholesterol, while fT4 was positively associated with diastolic blood pressure, FBG, and high-density lipoprotein-cholesterol (HDL-C), and negatively associated with hemoglobin A1c (HbA1c) and triglyceride. Finally, fT3/fT4 was positively associated with HbA1c and triglyceride, and negatively associated with HDL-C.

CONCLUSIONS

Overweight or obese participants had a high serum concentration of fT3, high fT3/fT4 ratio, and a low concentration of fT4. Underweight participants had high concentrations of fT4 and low concentrations of fT3. Thus, relationships between thyroid hormones and metabolic risk markers were identified which suggest that thyroid function might be one factor that influences body weight and the co-morbidities of obesity.

Thyroid Dysfunction and Diabetes Mellitus: Two Closely Associated Disorders

Thyroid dysfunction and diabetes mellitus are closely linked. Several studies have documented the increased prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. This review critically discusses the different underlying mechanisms linking type 1 and 2 diabetes and thyroid dysfunction to demonstrate that the association of these two common disorders is unlikely a simple coincidence. We assess the current state of knowledge on the central and peripheral control of thyroid hormone on food intake and glucose and lipid metabolism in target tissues (such as liver, white and brown adipose tissue, pancreatic β cells, and skeletal muscle) to explain the mechanism linking overt and subclinical hypothyroidism to type 2 diabetes and metabolic syndrome. We also elucidate the common susceptibility genes and the pathogenetic mechanisms contributing to the autoimmune mechanism involved in the onset of type 1 diabetes mellitus and autoimmune thyroid disorders. An untreated thyroid dysfunction can impair the metabolic control of diabetic patients, and this association can have important repercussions on the outcome of both of these disorders. Therefore, we offer recommendations for the diagnosis, management, and screening of thyroid disorders in patients with diabetes mellitus, including the treatment of diabetic patients planning a pregnancy. We also discuss the major causes of failure to achieve an optimal management of thyroid dysfunction in diabetic patients and provide recommendations for assessing and treating these disorders during therapy with antidiabetic drugs. An algorithm for a correct approach of these disorders when linked is also provided.

Thyroid Hormone Action and Energy Expenditure

Energy metabolism is one of the most recognized targets of thyroid hormone action, which indeed plays a critical role in modulating energy expenditure in all of its components. This is because thyroid hormone receptors are ubiquitous, and thyroid hormones interact and influence most metabolic pathways in virtually all systems throughout the entire life of the organism. The pleiotropic actions of thyroid hormone are the results of interaction between the local availability of T3 and the signal transduction machinery, which confer in physiologic conditions time and tissue specificity of the hormonal signal despite negligible variations in circulating levels. Historically, the measurement of energy expenditure has been used as the gold standard for the clinical assessment of the hormonal action until the advent of the immunoassays for TSH and thyroid hormone, which have since been used as proxy for measurement of thyroid hormone action. Although the clinical correlates between thyroid hormone action and energy expenditure in cases of extreme dysfunction (florid hyperthyroidism or hypothyroidism) are well recognized, there is still controversy on the effects of moderate, subclinical thyroid dysfunction on energy expenditure and, ultimately, on body weight trajectory. Moreover, little information is available on the effects of thyroid hormone replacement therapy on energy expenditure. This mini review is aimed to define the clinical relevance of thyroid hormone action in normal physiology and functional disorders, as well the effects of thyroid hormone therapy on energy expenditure and the effects of changes in energy status on the thyroid hormone axis.

Resolution of Hypothyroidism Restores Cold-Induced Thermogenesis in Humans

BACKGROUND

Hypothyroidism is a frequent endocrine disorder with common symptoms of increased cold sensitivity and unintended weight gain, indicating changes in energy expenditure (EE) and response to cold exposure. Thyroid hormones (TH) play an important role for proper function of brown adipose tissue (BAT) and cold-induced thermogenesis (CIT) in rodents, but the role of hypothyroidism on CIT in humans is uncertain.

METHODS

This was a prospective observational study. Forty-two patients presenting with subclinical or overt hypothyroidism in whom TH replacement was planned were recruited. Thirty-three patients completed the study. Thermogenesis was measured by indirect calorimetry during warm conditions and after a mild cold stimulus of 90 minutes, both during the hypothyroid state and after at least three months of sufficient TH replacement. CIT was determined as the difference between EE during mildly cold and warm conditions. The primary endpoint was the change of CIT between the hypothyroid and euthyroid state.

RESULTS

EE during warm conditions increased from a median of 1330 (interquartile range [IQR] 1251-1433) kcal/24 hours in the hypothyroid state to a median of 1442 (IQR 1294-1579) kcal/24 hours in the euthyroid state (+8.5%; p = 0.0002). EE during mild cold exposure increased from 1399 (IQR 1346-1571) kcal/24 hours to 1610 (IQR 1455-1674) kcal/24 hours (+15%; p < 0.0001). The median CIT was 55 (IQR 1-128) kcal/24 hours at the baseline visit, after restoration of euthyroidism CIT increased by 102% to a median of 111 (IQR 15.5-200) kcal/24 hours (p = 0.011). Serum levels of free thyroxine at the respective visit and mean outdoor temperature during the preceeding 30 days were significantly associated with CIT (p = 0.021 and p = 0.001, respectively).

CONCLUSION

Restoring euthyroidism significantly increases CIT in hypothyroid humans.

Effects of Altering Levothyroxine Dose on Energy Expenditure and Body Composition in Subjects Treated With LT4

BACKGROUND

It is unclear whether variations in thyroid status within or near the reference range affect energy expenditure, body mass, or body composition.

METHODS

138 subjects treated with levothyroxine (LT4) for hypothyroidism with normal TSH levels underwent measurement of total, resting, and physical activity energy expenditure; thermic effect of food; substrate oxidation; dietary intake; and body composition. They were assigned to receive an unchanged, higher, or lower LT4 dose in randomized, double-blind fashion, targeting one of three TSH ranges (0.34 to 2.50, 2.51 to 5.60, or 5.61 to 12.0 mU/L). The doses were adjusted every 6 weeks to achieve target TSH levels. Baseline measures were reassessed at 6 months.

RESULTS

At study end, the mean LT4 doses and TSH levels were 1.50 ± 0.07, 1.32 ± 0.07, and 0.78 ± 0.08 µg/kg (P < 0.001) and 1.85 ± 0.25, 3.93 ± 0.38, and 9.49 ± 0.80 mU/L (P < 0.001), respectively, in the three arms. No substantial metabolic differences in outcome were found among the three arms, although direct correlations were observed between decreases in thyroid status and decreases in resting energy expenditure for all subjects. The subjects could not ascertain how their LT4 dose had been adjusted but the preferred LT4 dose they perceived to be higher (P < 0.001).

CONCLUSIONS

Altering LT4 doses in subjects with hypothyroidism to vary TSH levels in and near the reference range did not have major effects on energy expenditure or body composition. Subjects treated with LT4 preferred the perceived higher LT4 doses despite a lack of objective effect. Our data do not support adjusting LT4 doses in patients with hypothyroidism to achieve potential improvements in weight or body composition.

The relationship between resting energy expenditure and thyroid hormones in response to short-term weight loss in severe obesity

Background

Regulating thermogenesis is a major task of thyroid hormones (THs), and involves TH-responsive energetic processes at the central and peripheral level. In severe obesity, little is known on the relationship between THs and resting energy expenditure (REE) before and after weight loss.

Methods

We enrolled 100 euthyroid subjects with severe obesity who were equally distributed between genders. Each was examined before and after completion of a 4-wk inpatient multidisciplinary dieting program and subjected to measurement of thyroid function, REE, fat-free mass (FFM, kg) and percent fat mass (FM).

Results

Baseline REE was lower than predicted in 70 obese patients, and overall associated with BMI, FFM and FM but not thyroid-related parameters. By the study end, both BMI and REE decreased (5.5% and 4.1%, p<0.001 vs. baseline) and their percent changes were significantly associated (p<0.05), while no association related percent changes of REE and FFM or FM. Individually, REE decreased in 66 and increased in 34 patients irrespective of gender, BMI and body composition. Weight loss significantly impacted TSH (-6.3%), FT3 (-3.3%) and FT4 levels (3.9%; p<0.001 for all). By the study end, a significant correlation became evident between REE and FT4 (r = 0.42, p<0.001) as well as FT3 (r = 0.24, p<0.05). In stepwise multivariable regression analysis, however, neither THs nor body composition entered the regression equation for REE response to weight loss.

Conclusions

In severe obesity, short-term weight loss discloses a positive relationship between REE and THs.

Subclinical Hypothyroidism among local adult obese population

OBJECTIVE

To determine the frequency of subclinical hypothyroidism in local adult obese population.

METHODS

The study was conducted at Hayatabad Medical Complex, Peshawar, from March, 2017 to August, 2017. All patients aged between 18 and 60 years with BMI of more than 29kg/m2 were included in the study. Patients on lipid lowering drugs, with renal failure, hepatic failure and already diagnosed cases of thyroid dysfunction were excluded from the study. Thyroid functions were measured for all patients.

RESULTS

A total of 127 adults were included in the study in a consecutive manner. Mean age was 34.5 + 7.9 years of which 46.5% were male and 53.5% were female. Mean BMI was 32.05±2.06 kg/m2. The mean serum TSH was 3.13±1.10 mIU/L and mean serum thyroxine level was 1.08±0.25ng/dl. Subclinical hypothyroidism was recorded in 15% of the study population.

CONCLUSION

Subclinical hypothyroidism is highly prevalent in our population with BMI of more than 29kg/m2. Further studies are recommended on relationship between thyroid functions and BMI and its effect on cardiovascular functions.

Thyroid-Stimulating Hormone, Degree of Obesity, and Metabolic Risk Markers in a Cohort of Swedish Children with Obesity

BACKGROUND/AIMS

Thyroid-stimulating hormone (TSH) is affected in obesity and might influence metabolic risk. It is unclear what mechanisms cause elevated TSH in obesity. We aimed to investigate TSH status within the normal range and the association of TSH with degree of obesity and metabolic parameters in children with obesity.

METHODS

A total of 3,459 children, aged 3.0-17.9 years, were identified in the Swedish Childhood Obesity Treatment Registry, BORIS. Age, gender, TSH, free triiodothyronine (fT3), free thyroxine (fT4), body mass index standard deviation scores (BMI SDS), as well as variables of lipid and glucose metabolism were examined.

RESULTS

Children with high-normal TSH (>3.0 mU/L) (28.8%) had higher BMI SDS compared to children with low-normal TSH (<3.0 mU/L) (p < 0.001). Multivariable regression analysis adjusted for age and gender showed that TSH levels were associated with BMI SDS (β: 0.21, 95% CI: 0.14-0.28, p < 0.001). Associations of thyroid hormones with markers of lipid and glucose metabolism were observed, where TSH was associated with fasting insulin, HOMA (homeostatic model assessment of insulin resistance), total cholesterol, and triglycerides.

CONCLUSIONS

A positive association between TSH levels and BMI SDS was seen in children with obesity. Associations of TSH and free thyroid hormones with glucose metabolism indicated that TSH might be one of several factors acting to determine body weight and obesity co-morbidities, although the underlying mechanism remains unclear.

Changes in Body Compositions and Basal Metabolic Rates during Treatment of Graves' Disease

OBJECTIVES

Because thyroid hormone is an important determinant of body weight and basal metabolic rate, we investigated the changes in the basal metabolic rate and body composition sequentially after treatment for Graves' disease.

METHODS

A prospective cohort study was performed with six women newly diagnosed with Graves' disease. During a 52-week treatment of methimazole, body composition, resting respiratory expenditure (REE), and handgrip strength were measured consecutively.

RESULTS

After methimazole treatment, body weight was initially increased (0-8 weeks), subsequently plateaued (8-24 weeks), and gradually decreased in the later period (24-52 weeks) despite the decreased food intake. The measured REE was 40% higher than the predicted REE at baseline, and it gradually decreased after treatment. REE positively correlated with thyroid hormone levels, peripheral deiodinase activity, and thyroid's secretory capacity. Body compositional analyses showed that the fat mass increased during an earlier period (4-12 weeks), while the lean mass increased significantly during the later period (26-52 weeks). Consistent with the lean mass changes, muscle strength also significantly increased during the later period.

CONCLUSIONS

Treatment of Graves' disease increased body weight and fat mass transiently with decreased REE. However, long-term compositional changes moved in a beneficial direction increasing lean mass and reinforcing muscle strength, following decreasing fat percentages.

FAT DISTRIBUTION AND METABOLIC PROFILE IN SUBJECTS WITH HASHIMOTO'S THYROIDITIS

CONTEXT

Previous studies have associated overt/subclinical hypothyroidism and obesity but have failed to confirm a causative relationship between them. Confusion is even more for subjects with Hashimoto's Thyroiditis (HT).

OBJECTIVE

In this study, we aimed to evaluate the fat distribution and metabolic profile of subjects with euthyroid HT as well as to establish an appropriate cut-off level of TSH for the development of metabolic syndrome (Mets) in both groups.

PATIENTS AND METHODS

All subjects were euthyroid whether under levothyroxine replacement or not. We recruited 301 volunteers (99 with HT and 202 without thyroid autoimmunity). Together with some metabolic variables, we measured the waist circumference, hip circumference, neck circumference manually; the total body fat with a body composition analyzer; and the visceral fat/trunk fat percentage via abdominal bioelectrical impedance analysis.

RESULTS

A significant positive correlation was established between TSH levels and insulin, fasting plasma glucose, HOMA-IR and body mass index (r=0.28; p<0.001; r=0.27; p<0.05: r=0.32; p<0.001: r=0.13; p<0.05 respectively). The prevalence of Metabolic Syndrome (Mets) was comparable in HT and control groups (27.3% vs. 30.7%; p>0.05). The prevalence of Mets was similar when HT subjects using levothyroxine or HT subjects with accompanying thyroid nodules were taken into consideration. Similarly, anthropometric and metabolic parameters were similar in both the HT group and the control group.We were unable to establish the TSH cut-off level by ROC analysis with desired sensitivity and specificity (AUC: 0.563 with 95% C.I. p=0.35; standard error 0.76).

CONCLUSIONS

Although weight gain is frequently encountered in subjects with HT, such subjects with thyroid function tests in the euthyroid range have a similar prevalence of Mets and similar metabolic and anthropometric measurements compared to subjects without autoimmunity.

Serum Thyroid-Stimulating Hormone Levels and Body Mass Index Percentiles in Children with Primary Hypothyroidism on Levothyroxine Replacement

OBJECTIVE

To determine the association, if any, between thyroid-stimulating hormone (TSH) levels and body mass index (BMI) percentiles in children with primary hypothyroidism who are chemically euthyroid and on treatment with levothyroxine.

METHODS

This retrospective cross-sectional study consisted of a review of medical records from RUSH Medical Center and Stroger Hospital, Chicago, USA of children with primary hypothyroidism who were seen in the clinic from 2008 to 2014 and who were chemically euthyroid and on treatment with levothyroxine for at least 6 months. The patients were divided into two groups based on their TSH levels (0.34-<2.5 mIU/L and ≥2.5-5.6 mIU/L). The data were analyzed by Spearman rank correlation, linear regression, cross tabulation and chi-square, Mann-Whitney U test, and Kruskal-Wallis test.

RESULTS

One hundred and forty-six children were included, of which 26% were obese (BMI ≥95%), 21.9% overweight (BMI ≥85-<95%), and 52.1% of a healthy weight (BMI ≥5-<85%). There was a significant positive correlation between TSH and BMI percentiles (r=0.274, p=0.001) and a significant negative correlation between TSH and serum free T4 (r=-0.259, p=0.002). In the lower TSH group, 68.4% of the children had a healthy weight, while the percentage of obese children was 60.5% in the upper TSH group (p=0.012).

CONCLUSION

In children diagnosed with primary hypothyroidism who are chemically euthyroid on treatment with levothyroxine, there is a positive association between higher TSH levels and higher BMI percentiles. However, it is difficult to establish if the higher TSH levels are a direct cause or a consequence of the obesity. Further studies are needed to establish causation beyond significant association.

Thyroid Function Variation in the Normal Range, Energy Expenditure, and Body Composition in L-T4-Treated Subjects

PURPOSE

It is not clear whether upper limits of the thyrotropin (TSH) reference range should be lowered. This debate can be better informed by investigation of whether variations in thyroid function within the reference range have clinical effects. Thyroid hormone plays a critical role in determining energy expenditure, body mass, and body composition, and therefore clinically relevant variations in these parameters may occur across the normal range of thyroid function.

METHODS

This was a cross-sectional study of 140 otherwise healthy hypothyroid subjects receiving chronic replacement therapy with levothyroxine (L-T4) who had TSH levels across the full span of the laboratory reference range (0.34 to 5.6 mU/L). Subjects underwent detailed tests of energy expenditure (total and resting energy expenditure, thermic effect of food, physical activity energy expenditure), substrate oxidation, diet intake, and body composition.

RESULTS

Subjects with low-normal (≤2.5 mU/L) and high-normal (>2.5 mU/L) TSH levels did not differ in any of the outcome measures. However, across the entire group, serum free triiodothyronine (fT3) levels were directly correlated with resting energy expenditure, body mass index (BMI), body fat mass, and visceral fat mass, with clinically relevant variations in these outcomes.

CONCLUSIONS

Variations in thyroid function within the laboratory reference range have clinically relevant correlations with resting energy expenditure, BMI, and body composition in L-T4-treated subjects. However, salutary effects of higher fT3 levels on energy expenditure may be counteracted by deleterious effects on body weight and composition. Further studies are needed before these outcomes should be used as a basis for altering L-T4 doses in L-T4-treated subjects.

Associations between adiposity and indicators of thyroid status in children and adolescents

BACKGROUND

In adults, obesity is associated with abnormalities of thyroid function; there are fewer studies in paediatric cohorts.

OBJECTIVES

To examine associations of weight and adiposity with indices of thyroid function and thyroid-related metabolic factors in children.

DESIGN/METHODS

A sample of 1203 children without obesity (body mass index [BMI] < 95th percentile; N = 631) and with obesity (BMI ≥ 95th percentile; N = 572), age 5-18 years, had height and weight measured (to calculate BMI-Z score for age and sex) and had blood collected in the morning for thyroid-stimulating hormone (TSH), free thyroxine (FT4) and leptin. A subset (N = 829) also underwent measurement of fat mass by dual-energy X-ray absorptiometry. Analyses examined associations of TSH and FT4 with adiposity and obesity-related conditions accounting for sociodemographic factors.

RESULTS

Thyroid-stimulating hormone was positively related to BMIz and fat mass (both p-values < 0.001). FT4 was negatively related to BMIz and fat mass (both p-values < 0.001). TSH was positively correlated to leptin (p = 0.001) even after accounting for fat mass.

CONCLUSIONS

Paediatric obesity is associated with higher TSH and lower FT4 concentrations and with a greater prevalence of abnormally high TSH. Leptin concentrations may in part explain obesity's effects on thyroid status, perhaps through leptin's effects on TSH secretion.

Recommendations for treatment of hypothyroidism with levothyroxine and levotriiodothyronine: a 2016 position statement of the Italian Society of Endocrinology and the Italian Thyroid Association

Levothyroxine (L-T4) is recommended as lifelong replacement therapy for hypothyroidism. Recent clinical and experimental data support the addition of levotriiodothyronine (L-T3) treatment in some selected hypothyroid patients when their symptoms persist and their quality of life remains impaired despite adequate L-T4 monotherapy. An increase in L-T3 prescriptions has been recently observed in Italy due to availability of different L-T3 formulations, making it possible to clinicians to prescribe L-T3 alone or in combination with L-T4. The aim of the present position statement was to define the correct clinical indications, schedule, duration of treatment and contraindications of combined treatment with L-T4 and L-T3 in hypothyroid patients in an attempt to guide clinicians and to avoid potential adverse effects of overtreatment.

Is a Normal TSH Synonymous With "Euthyroidism" in Levothyroxine Monotherapy?

CONTEXT

Levothyroxine (LT₄) monotherapy is the standard of care for hypothyroidism.

OBJECTIVE

To determine whether LT₄ at doses that normalize the serum TSH is associated with normal markers of thyroid status.

DESIGN

Cross-sectional data from the US National Health and Nutrition Examination Survey (2001-2012) was used to evaluate 52 clinical parameters. LT₄ users were compared to healthy controls and controls matched for age, sex, race, and serum TSH. Regression was used to evaluate for correlation with T₄ and T₃ levels.

PARTICIPANTS

A total of 9981 participants with normal serum TSH were identified; 469 were LT₄-treated.

RESULTS

Participants using LT₄ had higher serum total and free T₄ and lower serum total and free T₃ than healthy or matched controls. This translated to approximately 15-20% lower serum T₃:T₄ ratios in LT₄ treatment, as has been shown in other cohorts. In comparison to matched controls, LT₄-treated participants had higher body mass index despite report of consuming fewer calories/day/kg; were more likely to be taking beta-blockers, statins, and antidepressants; and reported lower total metabolic equivalents. A serum TSH level below the mean in LT₄-treated participants was associated with a higher serum free T₄ but similar free and total T₃; yet those with lower serum TSH levels exhibited higher serum high-density lipoprotein and lower serum low-density lipoprotein, triglycerides, and C-reactive protein. Age was negatively associated with serum free T₃:free T₄ ratio in all participants; caloric intake was positively associated in LT₄-treated individuals.

CONCLUSIONS

In a large population study, participants using LT₄ exhibited lower serum T₃:T₄ ratios and differed in 12/52 objective and subjective measures.

Elevated thyroid stimulating hormone levels are associated with metabolic syndrome in a Chinese community-based population of euthyroid people aged 40 years and older

This study investigated whether high-normal thyrotropin (TSH) levels are associated with metabolic syndrome in euthyroid Chinese people≥40 years old. Clinical and metabolic factors were assessed in 2,356 subjects (40-77 years old) with TSH levels in the normal range (0.35-5.00 mU/L). Using 2.50 mU/L as the cut-off point of TSH level within the normal range, we divided subjects into the high-TSH (2.50-5.00 mU/L; n = 1,064) and low-TSH (0.35-2.50 mU/L; n = 11,292) group. The results showed that the mean levels of body mass index (BMI), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), and fasting plasma glucose (FPG) were higher in the high-TSH group and TSH levels were significantly positively correlated with BMI, LDL-C, TC, and FPG. The prevalence of central obesity, hypertriglyceridemia, low high density lipoprotein cholesterol (HDL-C), and high FPG (>5.60 mmol/L) was significantly higher in females and subjects with high-TSH levels. Metabolic syndrome was also more prevalent in the high-TSH group. People over the age of 40 years with high-normal TSH levels had a 1.2-fold increased risk of metabolic syndrome, compared with those with low-normal TSH levels, after adjusting for age and gender. In conclusion, high normal TSH is a risk factor for metabolic syndrome in people≥40 years old.

Effects of Levothyroxine Replacement or Suppressive Therapy on Energy Expenditure and Body Composition

BACKGROUND

Thyrotropin (TSH)-suppressive doses of levothyroxine (LT4) have adverse effects on bone and cardiac function, but it is unclear whether metabolic function is also affected. The objective of this study was to determine whether women receiving TSH-suppressive LT4 doses have alterations in energy expenditure or body composition.

METHODS

This study was a cross-sectional comparison between three groups of women: 26 women receiving chronic TSH-suppressive LT4 doses, 80 women receiving chronic replacement LT4 doses, and 16 untreated euthyroid control women. Subjects underwent measurements of resting energy expenditure (REE), substrate oxidation, and thermic effect of food by indirect calorimetry; physical activity energy expenditure by accelerometer; caloric intake by 24-hour diet recall; and body composition by dual X-ray absorptiometry.

RESULTS

REE per kilogram lean body mass in the LT4 euthyroid women was 6% lower than that of the LT4-suppressed group, and 4% lower than that of the healthy control group (p = 0.04). Free triiodothyronine (fT3) levels were directly correlated with REE, and were 10% lower in the LT4 euthyroid women compared with the other two groups (p = 0.007). The groups of subjects did not differ in other measures of energy expenditure, caloric intake, or body composition.

CONCLUSIONS

LT4 suppression therapy does not adversely affect energy expenditure or body composition in women. However, LT4 replacement therapy is associated with a lower REE, despite TSH levels within the reference range. This may be due to lower fT3 levels, suggesting relative tissue hypothyroidism may contribute to impaired energy expenditure in LT4 therapy.

Relationship of anthropometric measurements to thyroid nodules in a Chinese population

OBJECTIVE

Previous studies have found that overweight and obesity are related to numerous diseases, including thyroid cancer and thyroid volume. This study evaluates the relationship between body size and the presence of thyroid nodules in a Chinese population.

METHODS

A total of 6793 adults and 2410 children who underwent thyroid ultrasonography were recruited in this cross-sectional study in Hangzhou, Zhejiang Province, China, from March to October, 2010. Sociodemographic characteristics and potential risk factors of thyroid nodules were collected by questionnaire. Height and weight were measured using standard protocols. Associations of height, weight, body mass index (BMI) and body surface area (BSA) with the presence of thyroid nodules were evaluated using multiple logistic regression models.

RESULTS

After adjustment for potential risk factors, an increased risk of thyroid nodule incidence was associated with height (OR 1.15, 95% CI 1.02 to 1.30), weight (OR 1.40, 95% CI 1.24 to 1.58), BMI (OR 1.26, 95% CI 1.11 to 1.42) and BSA (OR 1.43, 95% CI 1.27 to 1.62) in all adults, but most obviously in women. In children, similar associations were observed between risk of thyroid nodule incidence and weight, BMI and BSA, but not height. BSA was the measurement most significantly associated with thyroid nodules in both adults and children.

CONCLUSIONS

This study identified that the presence of thyroid nodules was positively associated with weight, height, BMI and BSA in both women and girls. It suggests that tall, obese individuals have increased susceptibility to thyroid nodules.

TRIAL REGISTRATION NUMBER

NCT01838629.

Influence of Hormonal Profile on Resting Metabolic Rate in Normal, Overweight and Obese Individuals

AIMS

To investigate whether blood thyroid stimulating hormone (TSH), cortisol, insulin and glucose concentrations (plus glucose:insulin ratio; GIR) could improve the accuracy of resting metabolic rate (RMR) prediction in normal, overweight and obese persons.

METHODS

Predictive equations were developed and compared against indirect calorimetry measures for RMR in 217 weight-control clinic participants (n = 128 males and n = 89 females: ∼24% normal weight, ∼39% overweight and ∼37% obese).

RESULTS

Using the common accuracy criteria of the proportion of predicted RMR within ±10% of measured RMR, our equations (using age, height, weight and gender, plus the blood factors, both independently and in combination) were accurate ∼36-44% of the time, for the whole sample, and when separated by gender and weight class. Specifically, the addition of the blood hormone and glucose concentrations improved the accuracy of predicted RMR by only 1-8% (NS).

CONCLUSIONS

Including blood TSH, cortisol, insulin, glucose and GIR into RMR prediction equations did not significantly improve estimation accuracy, which in any case only met a criterion of ±10% of the measured RMR ∼40% of the time. Further work to refine the prediction of RMR is still needed, and at present, direct measurements should be made wherever possible.

Selective Serotonin Reuptake Inhibitors and Night Sweats in a Primary Care Population

Objective

Several small published case reports have suggested that selective serotonin reuptake inhibitors (SSRIs) can cause night sweats. The purpose of this study was to investigate this possibility further and to explore possible associations between night sweats and other commonly prescribed medications.

Design

Cross-sectional, secondary data analysis.

Setting

Data were obtained during the Oklahoma Longitudinal Assessment of the Health Outcomes of Mature Adults, a longitudinal cohort study carried out in the Oklahoma Physicians Resource/Research Network.

Participants

413 adult primary care patients aged 65–94 years.

Interventions

Current regular use of one of 35 classes of medication.

Main Outcome Measures

At least moderate night sweats during the prior month.

Results

A total of 38 (9.2 %) reported night sweats. Age, gender, body mass index, and total number of medications taken regularly were not associated with night sweats. After adjusting for age and gender, SSRIs (odds ratio [OR] 3.01; 95 % confidence interval [CI] 1.26–7.19), angiotensin receptor blockers (ARBs) (OR 3.44; 95 % CI 1.36–8.69), and thyroid hormone supplements (OR 2.53; 95 % CI 1.24–5.15) were the only classes of medications associated with night sweats.

Conclusions

Use of SSRIs may well be associated with night sweats in older patients. Associations found between night sweats and ARBs and thyroid supplements warrant further study.

Phthalate exposure and childhood obesity

Phthalates are commonly used as plasticizers and vehicles for cosmetic ingredients. Phthalate metabolites have documented biochemical activity including activating peroxisome proliferator-activated receptor and antiandrogenic effects, which may contribute to the development of obesity. In vitro and in vivo studies suggest that phthalates have significant effects on the development of obesity, especially after prenatal exposure at low doses. Although few studies have examined the effects of phthalate on obesity development in humans, some work has shown that phthalates affect humans and animals similarly. In this paper, we review the possible mechanisms of phthalate-induced obesity, and discuss evidence supporting the role of phthalates in the development of obesity in humans.

Thyroid hormone regulation of metabolism

Thyroid hormone (TH) is required for normal development as well as regulating metabolism in the adult. The thyroid hormone receptor (TR) isoforms, α and β, are differentially expressed in tissues and have distinct roles in TH signaling. Local activation of thyroxine (T4), to the active form, triiodothyronine (T3), by 5'-deiodinase type 2 (D2) is a key mechanism of TH regulation of metabolism. D2 is expressed in the hypothalamus, white fat, brown adipose tissue (BAT), and skeletal muscle and is required for adaptive thermogenesis. The thyroid gland is regulated by thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH). In addition to TRH/TSH regulation by TH feedback, there is central modulation by nutritional signals, such as leptin, as well as peptides regulating appetite. The nutrient status of the cell provides feedback on TH signaling pathways through epigentic modification of histones. Integration of TH signaling with the adrenergic nervous system occurs peripherally, in liver, white fat, and BAT, but also centrally, in the hypothalamus. TR regulates cholesterol and carbohydrate metabolism through direct actions on gene expression as well as cross-talk with other nuclear receptors, including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR), and bile acid signaling pathways. TH modulates hepatic insulin sensitivity, especially important for the suppression of hepatic gluconeogenesis. The role of TH in regulating metabolic pathways has led to several new therapeutic targets for metabolic disorders. Understanding the mechanisms and interactions of the various TH signaling pathways in metabolism will improve our likelihood of identifying effective and selective targets.

Thyroid function and body weight: a community-based longitudinal study

Objective

Body weight and overt thyroid dysfunction are associated. Cross-sectional population-based studies have repeatedly found that thyroid hormone levels, even within the normal reference range, might be associated with body weight. However, for longitudinal data, the association is less clear. Thus, we tested the association between serum thyrotropin (TSH) and body weight in a community-based sample of adult persons followed for 11 years.

Methods

A random sample of 4,649 persons aged 18–65 years from a general population participated in the DanThyr study in 1997–8. We included 2,102 individuals who participated at 11-year follow-up, without current or former treatment for thyroid disease and with measurements of TSH and weight at both examinations. Multiple linear regression models were used, stratified by sex and adjusted for age, smoking status, and leisure time physical activity.

Results

Baseline TSH concentration was not associated with change in weight (women, P = 0.17; men, P = 0.72), and baseline body mass index (BMI) was not associated with change in TSH (women, P = 0.21; men, P = 0.85). Change in serum TSH and change in weight were significantly associated in both sexes. Weight increased by 0.3 kg (95% confidence interval [CI] 0.1, 0.4, P = 0.005) in women and 0.8 kg (95% CI 0.1, 1.4, P = 0.02) in men for every one unit TSH (mU/L) increase.

Conclusions

TSH levels were not a determinant of future weight changes, and BMI was not a determinant for TSH changes, but an association between weight change and TSH change was present.

In utero exposure to iodine-131 from Chernobyl fallout and anthropometric characteristics in adolescence

Prenatal exposure to external radiation has been linked to growth retardation among atomic bomb survivors in adolescence. It is unclear from previous studies whether in utero exposure to internal radiation such as iodine-131 (I-131), which concentrates in the thyroid gland, has an effect on physical growth. We examined the associations between estimated thyroid gland dose from prenatal exposure to I-131 and self-reported height and weight in a cohort of 2,460 individuals exposed to radioactive fallout from the 1986 Chernobyl nuclear accident [mean I-131 dose = 72 (mGy)] and screened for thyroid diseases in adolescence. Using multivariable linear regression models, we estimated the mean differences in height, weight and body mass index (BMI) per unit increase in dose (100 mGy) in models adjusted for gender, age at examination, type of residence (rural/urban) and presence of thyroid disease diagnosed at screening. All of the adjustment factors as well as the trimester of exposure were evaluated as potential modifiers of the dose response. Overall, no significant dose response was found for height (P = 0.29), weight (P = 0.14) or BMI (P = 0.16). We found significant modification of the dose response for weight and BMI by presence/absence of thyroid disease (P = 0.02 and P = 0.03, respectively), but not for other factors. In individuals without thyroid disease (n = 1,856), there was a weak, significant association between I-131 thyroid dose and higher weight (210 g per 100 mGy, P = 0.02) or BMI (70 g/m² per 100 mGy, P = 0.02) that depended on individuals (n = 52) exposed to ≥500 mGy. In individuals with thyroid disease (n = 579, 67.4% with simple diffuse goiter) no significant association with I-131 for weight (P = 0.14) or BMI (P = 0.14) was found. These results do not support the hypothesis that in utero exposure to I-131 at levels experienced by a majority of study subjects may be associated with meaningful differences in adolescent anthropometry. However, additional studies are needed to clarify whether in utero exposure to I-131 at levels > = 500 mGy may be associated with increases in weight/BMI and to evaluate the confounding or modifying role of thyroid disease, past iodine deficiency, maternal and prenatal/postnatal factors.

Clinical evaluation of various thyroid hormones on thyroid function

To clarify the clinical value of serums total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), and free thyroxine (FT4) and provide a more eligible and economic strategy to assess thyroid function. A total of 2,673 participants (500 patients with hyperthyroidism, 500 patients with hypothyroidism, and 1,673 healthy people) were involved in our study. Serums TT3, TT4, FT3, and FT4 and thyrotropin (TSH) were measured with VIDAS fluorescent enzyme immunoassay. The Pearson correlation between TT3, TT4, FT3, and FT4 and TSH was determined to identify the most important indicator for thyroid function besides TSH. The correlation of TT4, and FT4 with TSH was statistically significant in healthy individuals (P < 0.01), and the R-values were -0.065 and -0.152, respectively. The correlation of TT4, FT4, TT3, and FT3 with TSH was statistically significant in patients with hyperthyroidism, and the R-values were -0.241, -0.225, -0.195, and -0.176, respectively. The correlation of TT4, FT4, TT3, and FT3 with TSH was statistically significant in patients with hypothyroidism, and the R-values were -0.322, -0.262, -0.179, and -0.136, respectively. In our opinion, TSH and FT4 are the most valuable indicators in assessing thyroid function in a healthy population, and TSH and TT4 are the most meaningful in hyperthyroidism and hypothyroidism.

Thermogenic effect of glucose in hypothyroid subjects

The importance of thyroid hormone, catecholamines, and insulin in modification of the thermogenic effect of glucose (TEG) was examined in 34 healthy and 32 hypothyroid subjects. We calculated the energy expenditure at rest and during oral glucose tolerance test. Blood samples for determinations of glucose, plasma insulin, adrenaline (A), and noradrenaline (NA) were collected. It was found that TEG was lower in hypothyroid than in control group (19.68 ± 3.90 versus 55.40 ± 7.32 kJ, resp., P < 0.0004). Mean values of glucose and insulin areas under the curve were higher in women with hypothyroidism than in control group (286.79 ± 23.65 versus 188.41 ± 15.84 mmol/L·min, P < 0.003 and 7563.27 ± 863.65 versus 4987.72 ± 583.88 mU/L·min, P < 0.03 resp.). Maximal levels of catecholamines after glucose ingestion were higher in hypothyroid patients than in control subjects (Amax-0.69 ± 0.08 versus 0.30 ± 0.07 nmol/L, P < 0.0001, and NAmax-6.42 ± 0.86 versus 2.54 ± 0.30 nmol/L, P < 0.0002). It can be concluded that in hypothyroidism TEG and glucose tolerance are decreased while the adrenergic response to glucose administration is enhanced. Presumably, these changes are related to decreased insulin sensitivity and responsiveness to catecholamine action.

Preliminary findings on the influence of FTO rs9939609 and MC4R rs17782313 polymorphisms on resting energy expenditure, leptin and thyrotropin levels in obese non-morbid premenopausal women

Given that leptin, ghrelin and thyrotropin play a major role in the regulation of resting energy expenditure (REE) and that the FTO rs9939609 and the MC4R rs17782313 polymorphisms have been proposed to affect energy homeostasis, we hypothesized that both polymorphisms are associated with REE and that these relationships can be mediated by leptin, ghrelin and thyrotropin in obesity. Therefore, the present study aimed to examine the relationships between FTO rs9939609 and the MC4R rs17782313 with REE, leptin, ghrelin and thyrotropin levels in obese women. The study comprised 77 obese (body mass index 34.0 ± 2.8 kg/m(2)) women (age 36.7 ± 7 years). We measured body composition by dual-energy X-ray absorptiometry and REE by indirect calorimetry. We analysed fasting leptin, ghrelin and thyrotropin levels and the ratio of leptin to fat mass was calculated. Genotype distributions of the polymorphisms did not deviate from Hardy-Weinberg expectations (P values >0.2). Women carrying the A allele of the FTO rs9939609 had lower REE (1,580 ± 22 vs. 1,739 ± 35 kcal/day, P < 0.001) and higher leptin to fat mass ratio (1.33 ± 0.05 vs. 1.13 ± 0.08 ng/ml kg, P < 0.05) and thyrotropin levels (1.93 ± 0.10 vs. 1.53 ± 0.16 μU/ml, P < 0.05) regardless of age and body mass index. We found no significant influence of the MC4R rs17782313 on energy metabolism or biochemical variables. Our findings confirm that the A allele of the FTO rs9939609 is associated with lower REE and increased plasma leptin levels. We also found an association between the FTO rs9939609 and thyrotropin, suggesting the possible influence of FTO in the hypothalamic-pituitary-thyroid axis as a potential mechanism of the increased adiposity.

Differences and associations of metabolic and vitamin D status among patients with and without sub-clinical hypothyroid dysfunction

BACKGROUND

Sub-clinical hypothyroid dysfunction, a relatively understudied disorder in the Kingdom of Saudi Arabia (KSA), has significant clinical implications if not properly monitored. Also from KSA, more than 50% of the population suffer from hypovitaminosis D (<50 nmol/l). In this cross-sectional case-control study, we described the differences and associations in the metabolic patterns of adult Saudis with and without hypothyroid dysfunction in relation to their vitamin D status, PTH, calcium and lipid profile.

METHODS

A total of 94 consenting adult Saudis [52 controls (without subclinical hypothyroidism), 42 cases (previously diagnosed subjects)] were included in this cross-sectional study. Anthropometrics were obtained and fasting blood samples were taken for ascertaining lipid and thyroid profile, as well as measuring PTH, 25(OH) vitamin D and calcium.

RESULTS

Cases had a significantly higher body mass index than the controls (p < 0.001). Circulating triglycerides was also significantly higher in cases than the controls (p = 0.001). A significant positive association between HDL-cholesterol and PTH (R = 0.56; p = 0.001), as well as a negative and modestly significant negative association between LDL-cholesterol and PTH (R = - 20.0; p = 0.04) were observed. FT3 was inversely associated with circulating 25 (OH) vitamin D (R = -0.25; p = 0.01).

CONCLUSIONS

Patients with hypothyroid dysfunction possess several cardiometabolic risk factors that include obesity and dyslipidemia. The association between PTH and cholesterol levels as well as the inverse association between vitamin D status and FT3 needs to be reassessed prospectively on a larger scale to confirm these findings.

Thyroid hormones and the metabolic syndrome

BACKGROUND

Clustering of various metabolic parameters including abdominal obesity, hyperglycaemia, low high-density lipoprotein cholesterol, elevated triglycerides and hypertension have been used worldwide as metabolic syndrome to predict cardiometabolic risk. Thyroid dysfunction impacts on various levels of these components.

OBJECTIVES

The purpose of the present review is to summarize available data on thyroid hormone-dependent action on components of the metabolic syndrome.

METHODS

A PubMed search for any combination of hyperthyroidism, thyrotoxicosis or hypothyroidism and metabolic syndrome, blood pressure, hypertension, hyperlipidaemia, cholesterol, high-density lipoprotein cholesterol, glucose, diabetes mellitus, body weight or visceral fat was performed. We included papers and reviews published between 2000 and today but accepted also frequently cited papers before 2000.

RESULTS

There is convincing evidence for a major impact of thyroid function on all components of the metabolic syndrome, reflecting profound alterations of energy homeostasis at many levels.

CONCLUSION

Even though the interactions shown in animal models and man are complex, it is evident that insulin sensitivity is highest and adverse thyroid effects on the metabolic system are lowest in euthyroid conditions.

Thyroid hormones correlate with resting metabolic rate, not daily energy expenditure, in two charadriiform seabirds

Thyroid hormones affect in vitro metabolic intensity, increase basal metabolic rate (BMR) in the lab, and are sometimes correlated with basal and/or resting metabolic rate (RMR) in a field environment. Given the difficulty of measuring metabolic rate in the field—and the likelihood that capture and long-term restraint necessary to measure metabolic rate in the field jeopardizes other measurements—we examined the possibility that circulating thyroid hormone levels were correlated with RMR in two free-ranging bird species with high levels of energy expenditure (the black-legged kittiwake, Rissa tridactyla, and thick-billed murre, Uria lomvia). Because BMR and daily energy expenditure (DEE) are purported to be linked, we also tested for a correlation between thyroid hormones and DEE. We examined the relationships between free and bound levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) with DEE and with 4-hour long measurements of post-absorptive and thermoneutral resting metabolism (resting metabolic rate; RMR). RMR but not DEE increased with T3 in both species; both metabolic rates were independent of T4. T3 and T4 were not correlated with one another. DEE correlated with body mass in kittiwakes but not in murres, presumably owing to the larger coefficient of variation in body mass during chick rearing for the more sexually dimorphic kittiwakes. We suggest T3 provides a good proxy for resting metabolism but not DEE in these seabird species.

Mechanisms of Weight Regain following Weight Loss

Obesity is a world-wide pandemic and its incidence is on the rise along with associated comorbidities. Currently, there are few effective therapies to combat obesity. The use of lifestyle modification therapy, namely, improvements in diet and exercise, is preferable over bariatric surgery or pharmacotherapy due to surgical risks and issues with drug efficacy and safety. Although they are initially successful in producing weight loss, such lifestyle intervention strategies are generally unsuccessful in achieving long-term weight maintenance, with the vast majority of obese patients regaining their lost weight during followup. Recently, various compensatory mechanisms have been elucidated by which the body may oppose new weight loss, and this compensation may result in weight regain back to the obese baseline. The present review summarizes the available evidence on these compensatory mechanisms, with a focus on weight loss-induced changes in energy expenditure, neuroendocrine pathways, nutrient metabolism, and gut physiology. These findings have added a major focus to the field of antiobesity research. In addition to investigating pathways that induce weight loss, the present work also focuses on pathways that may instead prevent weight regain. Such strategies will be necessary for improving long-term weight loss maintenance and outcomes for patients who struggle with obesity.

Triiodothyronine (T3) and metabolic rate in adolescents with eating disorders: Is there a correlation?

AIM

To examine the correlation between T3 and resting energy expenditure (REE) in adolescent patients with eating disorders (ED) to assess whether T3 can be used to predict metabolic rate suppression and recovery.

METHODS

A retrospective chart review was performed on patients with ED (Anorexia Nervosa [AN], Bulimia Nervosa [BN], and Eating Disorder NOS [EDNOS]), aged 11-22 years, who had T3 and REE measured within 1 month (N=38 AN, 32 BN/EDNOS). REE was measured by indirect calorimetry (IC) and represented as the percentage of expected REE (%EREE) predicted by the Harris-Benedict equation. Pearson correlation coefficients were calculated to examine the relationship between T3 and %EREE and how each correlates with anthropometric data, laboratory values, and diagnosis.

RESULTS

T3 was significantly correlated with %EREE in the AN group but not in the total population or BN/EDNOS group. In the total study population, T3 alone correlated significantly with weight, Body Mass Index (BMI), BMI percentile, %Ideal Body Weight (%IBW), %Maximum Weight Lost (%MWL), LH, and estradiol. In the AN group, T3 and %EREE both correlated with BMI, BMI percentile, LH, and estradiol; however, only T3 correlated with %IBW and %MWL. In the BN/EDNOS group, T3 correlated with BMI, BMI percentile, %IBW, and estradiol while %EREE correlated with none.

CONCLUSION

In patients with AN, T3 correlated significantly with markers of malnutrition and %EREE and may serve as a surrogate measure when IC is unavailable. Following T3 during treatment of AN may assist clinicians in assessing metabolic suppression and recovery and help guide caloric prescriptions and goal weights.

Thyroid function and obesity

Important interaction exists between thyroid function, weight control, and obesity. Several mechanisms seem to be involved, and in studies of groups of people the pattern of thyroid function tests depends on the balance of obesity and underlying thyroid disease in the cohort studied. Obese people with a normal thyroid gland tend to have activation of the hypothalamic-pituitary-thyroid axis with higher serum TSH and thyroid hormones in serum. On the other hand, small differences in thyroid function are associated with up to 5 kg difference in body weight. The weight loss after therapy of overt hypothyroidism is caused by excretion of water bound in tissues (myxoedema). Many patients treated for hyperthyroidism experience a gain of more weight than they lost during the active phase of the disease. The mechanism for this excessive weight gain has not been fully elucidated. New studies on the relation between L-T3 therapy and weight control are discussed. The interaction between weight control and therapy of thyroid disease is important to many patients and it should be studied in more detail.