Raised serum TSH levels in patients with morbid obesity: is it enough to diagnose subclinical hypothyroidism?

Association of stress and primary hypothyroidism

Background

Hypothyroidism is the result of impaired production and secretion of thyroid hormones. The cardiovascular system is affected by fluctuations in thyroid hormone levels. Stressful events or stressors can affect the hypothalamic-pituitary-thyroid (HPT) axis and psychological and physiological responses. Stress increases thyroid hormone levels while decreasing TSH levels, which exacerbates autoimmune thyroid disease.

Aim

To evaluate the relationship between stress and primary hypothyroidism.

Methods

A total of 77 newly diagnosed hypothyroid patients (TSH >5.0 mIU/L) and 77 healthy adults (TSH 0.5-5.0 mIU/L) were enrolled. During a brief general physical examination, the following values were measured: height, weight, blood pressure, pulse, and pulse rate. A brief systemic examination of the cardiovascular system and lungs was also performed to rule out systemic diseases. Heart rate variability (HRV) processing and analysis were performed using Pro LabChart (PowerLab 8Pro) data analysis software from AD Instrument.

Results

Mean Avg. RR was significantly higher, RM SSD and pRR50 were significantly lower in cases than in controls. Mean HF was significantly lower and LF/HF (frequency range) was significantly higher in cases than in controls. Mean PSS was significantly higher in cases (25.82 ± 2.83) than in controls (22.47 ± 2.10). The majority of cases (54.5%) had a high stress level. The TSH level showed a highly significant correlation with the LF/HF ratio and with the PSS score.

Conclusion

The mean Avg. RR and HF were significantly higher, RM SSD and pRR50 and LF/HF (frequency range) were significantly lower in hypothyroid patients.

Total weight loss induces the alteration in thyroid function after bariatric surgery

Background

Bariatric surgery is an effective approach to weight loss, which may also affect thyroid function. However, alteration in thyroid-stimulating hormone (ΔTSH) and thyroid hormones after bariatric surgery and the relationship between thyroid function and postoperative weight loss still remains controversial.

Methods

Data were collected from euthyroid patients with obesity who underwent sleeve gastrectomy and Roux-en-Y gastric bypass from 2017 to 2022. The alterations of free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), total triiodothyronine (TT3), and TSH were calculated 1 year after surgery. Pearson correlation analysis was used to assess the correlation between the percentage of total weight loss (%TWL) and ΔTSH. Multivariable linear regression was utilized to determine the association between %TWL and ΔTSH.

Results

A total of 256 patients were included in our study. The mean %TWL was 28.29% after 1 year. TSH decreased from 2.33 (1.67, 3.04) uIU/mL to 1.82 (1.21, 2.50) uIU/mL (P < 0.001), FT3 decreased from 3.23 ± 0.42 pg/mL to 2.89 ± 0.41 pg/mL (P < 0.001), FT4 decreased from 1.11 ± 0.25 ng/dL to 1.02 ± 0.25 ng/dL (P < 0.001), TT3 decreased from 1.13 (1.00, 1.25) ng/mL to 0.89 (0.78, 1.00) ng/mL (P < 0.001), and TT4 decreased from 8.28 ± 1.69 ug/mL to 7.82 ± 1.68 ug/mL 1 year postoperatively (P < 0.001). %TWL was found to be significantly correlated to ΔTSH by Pearson correlation analysis (Pearson correlation coefficient = 0.184, P = 0.003), indicating that the more weight loss, the more TSH declined. After adjusting for covariates in multivariable linear regression, %TWL was found to be independently associated with ΔTSH (β = 0.180 [95% confidence interval (CI), 0.048 - 0.312], P = 0.008). Moreover, %TWL was divided into 3 categorical groups (%TWL ≤ 25%, 25% < %TWL ≤ 35%, and %TWL > 35%) for further exploration, and was also found to be an independent predictor for ΔTSH after adjusting for covariates in multivariable linear regression (β = 0.153 [95% CI, 0.019 - 0.287], P = 0.025).

Conclusion

TSH, FT4, FT3, TT4, and TT3 decrease significantly 1 year after bariatric surgery. The decline in TSH is independently mediated by postoperative weight loss; the more the weight loss, the more the TSH decrease.

Low-Glycemic Load Diets and Thyroid Function: A Narrative Review and Future Perspectives

Nutrition and calorie intake are associated with subtle changes of thyroid function tests in subjects with an intact Hypothalamic-Pituitary-Thyroid axis. Iodine deficiency and extreme fluctuations in calorie intake, such as those that occur during periods of starvation or overfeeding could lead to alterations in thyroid hormones. The dietary macronutrient and micronutrient composition could also influence the thyroid function. Recently, Low-Glycemic Load (LGL) diets have become very popular and are effective in the treatment and/or prevention of several medical conditions, including diabetes, obesity, cardiovascular disease, and epilepsy. In this review, we report on the available data from the literature regarding the association between LGL diets and thyroid function or dysfunction. Several studies conducted in this field to date have yielded inconsistent results.

Causal association between obesity and hypothyroidism: a two-sample bidirectional Mendelian randomization study

Introduction

Previous observational studies have reported a positive correlation between obesity and susceptibility to hypothyroidism; however, there is limited evidence from alternative methodologies to establish a causal link.

Methods

We investigated the causal relationship between obesity and hypothyroidism using a two-sample bidirectional Mendelian randomization (MR) analysis. Single-nucleotide polymorphisms (SNPs) associated with obesity-related traits were extracted from a published genome-wide association study (GWAS) of European individuals. Summarized diagnostic data of hypothyroidism were obtained from the UK Biobank. Primary analyses were conducted using the inverse variance-weighted (IVW) method with a random-effects model as well as three complementary approaches. Sensitivity analyses were performed to ascertain the correlation between obesity and hypothyroidism.

Results

MR analyses of the IVW method and the analyses of hypothyroidism/myxedema indicated that body mass index (BMI) and waist circumference (WC) were significantly associated with higher odds and risk of hypothyroidism. Reverse MR analysis demonstrated that a genetic predisposition to hypothyroidism was associated with an increased risk of elevated BMI and WC, which was not observed between WC adjusted for BMI (WCadjBMI) and hypothyroidism.

Discussion

Our current study indicates that obesity is a risk factor for hypothyroidism, suggesting that individuals with higher BMI/WC have an increased risk of developing hypothyroidism and indicating the importance of weight loss in reducing the risk of hypothyroidism.

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

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

A Systematic Review and Meta-Analysis of Free Triiodothyronine (FT3) Levels in Humans Depending on Seasonal Air Temperature Changes: Is the Variation in FT3 Levels Related to Nonshivering Thermogenesis?

Thyroid hormones play a crucial role in regulating normal development, growth, and metabolic function. However, the controversy surrounding seasonal changes in free triiodothyronine (FT3) levels remains unresolved. Therefore, the aim of this study was to conduct a systematic review and meta-analysis of variations in FT3 levels in relation to seasonal air temperatures in the context of current knowledge about its role in nonshivering thermogenesis. Ten eligible articles with a total of 336,755 participants were included in the meta-analysis. The studies were categorized into two groups based on the air temperature: "Cold winter", where the winter temperature fell below 0 °C, and "Warm winter", where the winter temperature was above 0 °C. The analysis revealed that in cold regions, FT3 levels decreased in winter compared to summer (I2 = 57%, p < 0.001), whereas in warm regions, FT3 levels increased during winter (I2 = 28%, p < 0.001). These findings suggest that seasonal variations in FT3 levels are likely to be influenced by the winter temperature. Considering the important role of the FT3 in the nonshivering thermogenesis process, we assume that this observed pattern is probably related to the differences in use of thyroid hormones in the brown adipose tissue during adaptive thermogenesis, which may depend on intensity of cold exposure.

The Impact of Laparoscopic Sleeve Gastrectomy on Thyroid Functions in Egyptian Patients with Obesity

BACKGROUND

Sleeve gastrectomy (SG) continues to be one of the most popular bariatric procedures all over the world. Thyroid-stimulating hormone (TSH) frequently shows a slight elevation in patients with obesity. The effect of SG on thyroid hormones has been rarely investigated.

AIM OF THE STUDY

This study aimed to assess the short-term effect of SG on thyroid functions in Egyptian patients with morbid obesity and the potential predictors of the postoperative thyroid functions.

PATIENTS AND METHODS

This study included patients undergoing SG at kasr al ainy hospitals. The patients underwent preoperative 3-, 6-, and 12-month postoperative analyses of the thyroid functions and other biochemical markers.

RESULTS

The study included 106 patients who showed significant improvement in thyroid functions at the follow-up assessment. Twelve-month TSH positively correlated with the 12-month measures of LDL and HbA1c. TSH change at 12-month follow-up (TSH) was inversely correlated to 12-month BMI and positively correlated to preoperative TSH and 12-month percentage of total weight loss (TWL%). Univariable linear regression analysis demonstrated that preoperative TSH (p < 0.001), 12-month TWL% (p = 0.042), 12-month HbA1c (p = 0.001), and 12-month LDL (p = 0.049) were significant predictors for the 12-month TSH levels. Multivariable analysis showed that only preoperative TSH levels (p < 0.001) and 12-month HbA1c levels (p = 0.021) could affect the 12-month TSH levels.

CONCLUSION

The current study supports the evidence of thyroid function improvement after sleeve gastrectomy. This improvement was affected by the amount of weight loss after surgery.

Unexplained Hyperthyrotropinemia: A Biochemical and Clinical Challenge

BACKGROUND

A raised serum TSH in the absence of a clear etiology, or "unexplained hyperthyrotropinemia" (UH), can be challenging for clinicians. The aim of the present study was to evaluate potential strategies aimed at a clinical and biochemical characterization of UH patients.

METHODS

We compared 36 patients with UH with a control group of 14 patients with chronic autoimmune thyroiditis (CAT) and subclinical hypothyroidism. The two groups were compared in terms of the following: (i) the rate of normalization of TSH after repeating with another assay; (ii) the rate of normalization of TSH over time with the same assay; (iii) the reduction in TSH after precipitation with polyethilenglycole (PEG); and (iv) free thyroxine (FT4) levels.

RESULTS

Similar TSH levels were observed in UH [5.65 (5.21-6.37)] and CAT [5.62 (5.17-8.50)] (p = 0.489). TSH measurement with another assay method showed a normal TSH value in 41.9% of UH vs. 46.1% of CAT patients (p = 0.797). After repeating the TSH measurement in time with the same assay method, an increased TSH value was confirmed in all cases, in both groups (0% in the UH group vs. 0% in the CAT group, p = 1.000). TSH recovery after PEG precipitation was similar in the two groups (% precipitable post-PEG: 68.75 ± 3.14 in UH vs. 68.67 ± 7.18 in CAT, p = 0.960). FT4 levels were similar in the two groups (FT4 1.02 ± 0.20 ng/dl in UH vs. 1.00 ± 0.20 ng/dl in CAT, p = 0.789).

CONCLUSIONS

The results do not support the concept that laboratory interferences are more frequent in UH patients, suggesting that patients with UH should be managed in the same way as patients with CAT until proven otherwise.

Levothyroxine therapy, calculated deiodinases activity and basal metabolic rate in obese or nonobese patients after total thyroidectomy for differentiated thyroid cancer, results of a retrospective observational study

INTRODUCTION

Therapy for hypothyroid obese patients is still under definition since the thyrotropin-stimulating hormone (TSH) level is a less reliable marker of euthyroidism than nonobese patients. Indeed, TSH levels positively correlate with body mass index (BMI), and this increase may be a compensatory mechanism aimed at increasing energy expenditure in obese people. In contrast, the correlation of BMI with thyroid hormone levels is not completely clear, and conflicting results have been obtained by several studies. The L-T4 replacement dose is more variable in obese hypothyroid patients than in nonobese patients, and a recent study indicated that the L-T4 replacement dose is related to lean body mass in obese thyroidectomized patients. We aimed to study the correlations of L-T4-administered dose, thyroid hormone levels and TSH secretion with basal metabolic rate (BMR) and total calculated deiodinase activity (GD) in obese and nonobese athyreotic patients. We also looked for individualized L-T4 replacement dose set points to be used in clinical practice.

METHODS

We studied retrospectively 160 athyreotic patients, 120 nonobese and 40 obese. GD was calculated by SPINA Thyr 4.2, the responsiveness of the hypothalamic/pituitary thyrotrope by Jostel's thyrotropin (TSH) index and BMR by the Mifflin-St. Jeor formula, the interplay of GD and BMR with L-T4, thyroid hormones and TSH index (TSHI) was also evaluated.

RESULTS

In our study, the L-T4 dose was an independent predictor of GD, and approximately 30% of athyreotic patients under L-T4 therapy had a reduced GD; FT4 levels were higher and negatively modulated by BMR in obese athyreotic patients respect to nonobese, in these patients a T4 to T3 shunt, in terms of TSHI suppression is observed suggesting a defective hypothalamic pituitary T4 to T3 conversion and a resistance to L-T4 replacement therapy.

CONCLUSIONS

L-t4 dose is the most important predictor of GD, BMR modulates T4 levels in obese athyreotic patients that are resistant to L-T4 replacement therapy.

Subclinical hypothyroidism, outcomes and management guidelines: a narrative review and update of recent literature

Subclinical hypothyroidism (SCH) is diagnosed when serum thyroid stimulation hormone (thyrotropin; TSH) levels are above the reference range, accompanied by levels of free thyroxine within its reference range. The management of SCH remains a diagnostic and therapeutic challenge despite many years of research relating to its epidemiology, aetiology, effectiveness of treatment and safety. European Thyroid Association (ETA) guidelines for the management of SCH were published almost a decade ago. This narrative review summarizes the clinical literature relating to SCH and outcomes since the publication of these guidelines. Clinical evidence emerging during the previous decade generally supports the view that SCH is associated with adverse outcomes to an extent that is intermediate between euthyroidism and overt hypothyroidism although evidence that treatment with thyroid hormone replacement is beneficial is lacking. Accordingly, the rationale for the recommendations for intervention in the ETA guidelines based on the age of the patient, level of serum TSH, symptoms and comorbidities remains valid today.

Serum TSH, 25(OH) D and phosphorus levels predict weight loss in individuals with diabetes/prediabetes and morbid obesity: a single-center retrospective cohort analysis

BACKGROUND

To evaluate the association of vitamin D and thyroid-stimulating hormone (TSH) with weight loss (WL) percentage (%) in patients with diabetes/prediabetes and Class II/III obesity.

METHODS

A retrospective cohort study was designed. Data were collected from a database of a referral endocrinology clinic that is prospectively and systematically generated. After exclusion of unavailable cases, the study enrolled 285 patients (51 ± 11 years old, female/male = 208/77; diabetes/prediabetes = 159/126; no/on levothyroxine replacement = 176/109; Class II/III obesity = 184/101, respectively) who maintained euthyroidism and were followed up for ≥6 months. The data were analyzed to determine the predictors of WL%.

RESULTS

Compared with baseline, in the median 22 months of follow-up, the whole study group lost 5.1% of their baseline body weight. As most obesity management trials define success as 'at least 10% of WL compared to baseline', we stratified the patients based on WL% extents. The distribution was as follow: Group 1 (n = 61) lost ≥10% body weight, Group 2 (n = 162) lost < 10% body weight, while Group 3 (n = 62) gained weight by the final visit. In groups 1 and 2 (weight losers), the serum thyroid stimulatig hormone (TSH) and parathyroid hormone (PTH) levels decreased and the free thyroxine (fT4), calcium, phosphorus, and 25-hydroxyvitamin D (25(OH)D) levels increased. In Group 3 (weight gainers), these changes were not observed (except for an increase in calcium levels). Regression analysis revealed that the final visit TSH (β = - 0.14, p < 0.05), 25(OH) D (β = 0.15, p < 0.05), and phosphorus (β = 0.20, p < 0.05) levels predicted WL%. However, if patients with autoimmune thyroiditis were excluded from the analysis, the decrease in TSH levels was not statistically significant.

CONCLUSIONS

Serum TSH, phosphorus, and 25(OH) D levels predict WL% in euthyroid patients with diabetes/prediabetes and morbid obesity. TSH predictivity seems to be a function of thyroid autoimmunity present with increased frequency in this cohort. Greater levels of phosphorus within the reference range and a sufficient vitamin D status are associated with a greater WL%.

Possible added value of thyroglobulin antibody (TgAb) testing in the evaluation of thyroidal status of subjects with overweight or obesity

PURPOSE

An increase in serum TSH concentrations in the absence of thyroid disease, named isolated hyperthyrotropinemia, is frequently observed in subjects with obesity. It is directly associated with body mass index, and it is reversible following weight loss. Autoimmune hypothyroidism is frequently associated with obesity, it is usually progressive and needs replacement treatment with L-thyroxine. The aim of this study was to investigate the role of thyroglobulin antibodies (TgAb) to define the thyroidal status in subjects with overweight or obesity.

METHODS

This is a retrospective study including 749 consecutive adult patients with overweight or obesity. Of those, 76 were excluded from the analysis due to hyperthyroidism, previous thyroidectomy or radioiodine therapy for hyperthyroidism, hemiagenesis or drug-induced hypothyroidism. Serum thyrotropin (TSH), free thyroxine (FT4), free 3,5,3'-triiodothyronine (FT3), TgAb and thyroperoxidase antibodies (TPOAb) were measured in all patients.

RESULTS

Out of 673 patients, 408 did not have thyroid disease. Among patients with thyroid disease (n = 265), 130 had nodular disease with no humoral signs of thyroid autoimmunity and 135 (20%) had autoimmune thyroiditis, defined by the presence of TPOAb and/or TgAb. The prevalence of hyperthyrotropinemia, either directly measured or presumed based on L-thyroxine treatment at the time of data collection, was 63.9% in patients with both TgAb and TPOAb, 47.1% in those with isolated positivity of TPOAb, 42.8% in patients with isolated positivity of TgAb, and 14.5% in those with no detectable TgAb or TPOAb.

CONCLUSIONS

Our results confirm a high prevalence of autoimmune thyroiditis (20%) in patients with obesity. TgAb may be associated with hypothyroidism in the absence of TPOAb. TgAb measurement may turn helpful to unravel a proportion of subjects that may have or may develop primary hypothyroidism requiring specific substitutive treatment.

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

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

Thyroid-Stimulating Hormone and Thyroid Hormones and Incidence of Diabetes: Prospective Results of the Brazilian Longitudinal Study of Adult Health (ELSA-BRASIL)

Background: There are conflicting data regarding the association of thyroid function with incident diabetes. We prospectively investigated thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), and its conversion ratio (fT3:fT4) with the risk of developing diabetes in euthyroid subjects and those with subclinical thyroid dysfunction. Our hypothesis is that this relationship is a U-shaped curve since both subclinical thyroid diseases may be associated with diabetes. Methods: ELSA-Brasil is a highly admixed cohort study of 35-74 years old at baseline (2008-2010). Levels of TSH, fT4, fT3, and fT3:fT4 ratio were evaluated at baseline and incident diabetes was estimated over an 8.2-year follow-up (2017-2019). Diabetes was identified based on medical diagnosis, prescriptions, and laboratory tests. The risk of diabetes was evaluated according to quintiles of TSH, fT4, fT3, and fT3:fT4 ratio using Poisson regression with robust variance presented as relative risk (RR) with confidence interval [CI] of 95% after multivariable adjustment for sociodemographic and cardiovascular risk factors (reference third quintile), and as continuous variables. Results: We included 7948 participants (mean age, 50.2 [standard deviation 8.6] years; 54.4% female): 7177 euthyroid, 726 with subclinical hypothyroidism, and 45 with subclinical hyperthyroidism. Incidence of diabetes was 14.8%. No association was found for TSH, fT4, fT3, and fT3:fT4 ratio quintiles with incident diabetes. Using continuous variables, the increase of 1-unit (1-U) of fT4 decreased the risk of diabetes (RR 0.94 [CI 0.91-0.99]), while the increase of 1-U of the fT3:fT4 ratio increased the diabetes risk (RR 1.37 [CI 1.15-1.63]). The increase of 1-U of fT3 was associated with an increased risk of diabetes, but without significance after multivariable adjustment. In body mass index-stratified analysis, people with overweight or obesity presented a modest significantly higher risk of diabetes in the lowest quintile of fT4 (RR 1.04 [CI 1.01-1.07]) and an inverse association with incident diabetes in the first quintile of fT3:fT4 ratio (RR, 0.95 [CI 0.93-0.98]). The analyses using continuous variables presented similar findings. Conclusion: These findings suggest that fT4 and fT3 levels and the conversion rate might be additional risk factors associated with incident diabetes, especially in the presence of overweight or obesity. However, they need to be confirmed in future studies. (ClinicalTrials.gov Identifier: NCT02320461).

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

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

Thyroid Function Alteration in Obesity and the Effect of Bariatric Surgery

The most common endocrine disease in obesity is hypothyroidism and secondary endocrine alterations, including abnormal thyroid function, are frequent in obesity. It is unclear whether impaired thyroid function is the cause or the consequence of increased adiposity; furthermore, there are no clear data regarding the best way to dose levothyroxine for patients with both hypothyroidism and obesity, and the effect of bariatric surgery (BS). The aim of the present article is to review some controversial aspects of the relation between obesity and the thyroid: (1) Thyroid function in obesity and the effect of BS (2) Thyroid hormone treatment (THT) in obese patients with hypothyroidism and the effect of BS. In summary: In morbidly obese patients, TSH is moderately increased. Morbid obesity has a mild central resistance to the thyroid hormone, reversible with weight loss. In morbidly obese hypothyroid patients, following weight loss, the levothyroxine dose/kg of ideal weight did not change, albeit there was an increment in the levothyroxine dose/kg of actual weight. From a clinical practice perspective, in morbid obesity, diagnosing mild hypothyroidism is difficult, BS improves the altered thyroid function and THT can be adapted better if it is based on ideal weight.

Inflammasome activation as a link between obesity and thyroid disorders: Implications for an integrated clinical management

Obesity is strongly associated with chronic low-grade inflammation. Obese patients have an increased risk to develop thyroid autoimmunity and to became hypothyroid, suggesting a pathogenetic link between obesity, inflammation and autoimmunity. Moreover, type 2 diabetes and dyslipidemia, also characterized by low-grade inflammation, were recently associated with more aggressive forms of Graves' ophthalmopathy. The association between obesity and autoimmune thyroid disorders may also go in the opposite direction, as treating autoimmune hyper and hypothyroidism can lead to weight gain. In addition, restoration of euthyroidism by L-T4 replacement therapy is more challenging in obese athyreotic patients, as it is difficult to maintain thyrotropin stimulation hormone (TSH) values within the normal range. Intriguingly, pro-inflammatory cytokines decrease in obese patients after bariatric surgery along with TSH levels. Moreover, the risk of thyroid cancer is increased in patients with thyroid autoimmune disorders, and is also related to the degree of obesity and inflammation. Molecular studies have shown a relationship between the low-grade inflammation of obesity and the activity of intracellular multiprotein complexes typical of immune cells (inflammasomes). We will now highlight some clinical implications of inflammasome activation in the relationship between obesity and thyroid disease.

The pattern of TSH and fT4 levels across different BMI ranges in a large cohort of euthyroid patients with obesity

PURPOSE

A multifold association relates the hypothalamo-pituitary-thyroid axis to body weight. The potential underlying mechanisms are incompletely understood. Further, the mild severity of obesity and the small proportion of individuals with obesity in so far published cohort studies provide little insights on metabolic correlates of thyroid function in obesity.

METHODS

We retrospectively enrolled 5009 adults with obesity (F/M, 3448/1561; age range, 18-87 years; BMI range, 30.0-82.7 kg/m²), without known thyroid disease in a study on TSH and fT4 levels, lipid profile, glucose homeostasis and insulin resistance, anthropometric parameters including BIA-derived fat mass (%FM) and fat-free mass (FFM).

RESULTS

The overall reference interval for TSH in our obese cohort was 0.58-5.07 mIU/L. As subgroups, females and non-smokers showed higher TSH levels as compared to their counterparts (p<0.0001 for both), while fT4 values were comparable between groups. There was a significant upward trend for TSH levels across incremental BMI classes in females, while the opposite trend was seen for fT4 levels in males (p<0.0001 for both). Expectedly, TSH was associated with %FM and FFM (p<0,0001 for both). TSH and fT4 showed correlations with several metabolic variables, and both declined with aging (TSH, p<0.0001; fT4, p<0.01). In a subgroup undergoing leptin measurement, leptin levels were positively associated with TSH levels (p<0.01). At the multivariable regression analysis, in the group as a whole, smoking habit emerged as the main independent predictor of TSH (β=-0.24, p<0.0001) and fT4 (β=-0.25, p<0.0001) levels. In non-smokers, %FM (β=0.08, p<0.0001) and age (β=-0.05, p<0.001) were the main significant predictors of TSH levels. In the subset of nonsmokers having leptin measured, leptin emerged as the strongest predictor of TSH levels (β=0.17, p<0.01).

CONCLUSIONS

Our study provides evidence of a gender- and smoking-dependent regulation of TSH levels in obesity.

Association between thyroid dysfunction and type 2 diabetes: a meta-analysis of prospective observational studies

BACKGROUND

Diabetes mellitus and thyroid disease are two areas of broad interest in the field of endocrinology and metabolism. Variation of thyroid hormone concentration, even within the normal range, may portend the onset of type 2 diabetes mellitus (T2DM), especially among those with prediabetes. However, current evidence is mixed.

METHODS

Prospective studies which assessed diabetes incidence were identified using a database search of MEDLINE and Embase through May 1, 2021. The Sidik-Jonkman random-effects model and cubic spline model were used to evaluate the associations and dose-response relationships between thyroid function/hormone levels and risk of T2DM and cardiovascular disease (CVD) risk among T2DM patients.

RESULTS

A total of 12 prospective studies were included. We found that high baseline TSH levels were related to a 17% higher risk of T2DM (RR 1.17, 95% CI 1.01, 1.36; I²=78%, P<0.01), compared with normal TSH levels. Low FT3 (RR 1.40, 95% CI 1.09, 1.80; I²=59%, P=0.03) and low FT4 (RR 1.33, 95% CI 1.04, 1.71; I²=62%, P=0.02) levels were significantly associated with risk of T2DM. The cubic spline model indicated a J-shaped relationship with TSH, but inverted-J-shaped relationships with FT3 and FT4. CVD events and all-cause deaths were prospectively evaluated in four studies, but were not associated with abnormal thyroid function.

CONCLUSIONS

Our meta-analysis determined that abnormal thyroid hormone level is associated with an increased risk of T2DM, showing a J-shaped relationship with TSH and inverted-J-shaped relationships with FT3 and FT4.

TRIAL REGISTRATION

Registered number in PROSPERO: CRD42021225695 .

Thyroid Volume and Thyroid Function Parameters Are Independently Associated with Weight Status in Overweight Children

BACKGROUND

A relation between thyroid-stimulating hormone (TSH), insulin resistance - both of which are related to obesity - and thyroid volume has been suggested. Therefore, we analyzed thyroid volume and structure in relation to thyroid function parameters, weight status, and insulin resistance.

METHODS

This is a cross-sectional study in which weight status (BMI-SDS), thyroid function parameters (TSH, free tri-iodothyronine [fT3], and free thyroxine [fT4]), insulin resistance index (HOMA-IR), and thyroid volume (ultrasound) were determined in 617 overweight children (aged 10.4 ± 2.2 years, 50% male, BMI-SDS 2.5 ± 0.6) and in 27 normal-weight children of a similar age and gender. Furthermore, changes in thyroid volume and structure, and thyroid function parameters were analyzed in 83 obese children (51% male, mean age 10.3 ± 2.2) at baseline and at the end of a 1-year lifestyle intervention.

RESULTS

Overweight children had a significant greater thyroid volume (4.2 ± 1.8 vs. 4.1 ± 0.5 mL) and higher TSH (3.1 ± 1.5 vs. 2.4 ± 1.1 mU/L) and fT3 (4.4 ± 0.7 vs. 4.1 ± 0.5 pg/mL) concentrations compared to normal-weight children. In multiple linear regression analyses adjusted to multiple confounders, thyroid volume was significantly related to BMI-SDS (b coefficient 0.44 ± 0.10, r2 = 0.41) but not to any thyroid function parameter or HOMA-IR. Changes in BMI-SDS were significantly associated with changes in thyroid volume (r = 0.22). The changes in thyroid volume were not correlated to changes of any thyroid function parameter or HOMA-IR.

CONCLUSIONS

Thyroid volume is positively correlated to weight status in childhood obesity and the change is reversible after weight loss independently of thyroid function parameters and insulin resistance. Further studies are needed to understand why thyroid volume is increased reversibly in overweight children.

T4+T3 Combination Therapy: An Unsolved Problem of Increasing Magnitude and Complexity

Thyroxine (T4)+triiodothyronine (T3) combination therapy can be considered in case of persistent symptoms despite normal serum thyroid stimulating hormone in levothyroxine (LT4)-treated hypothyroid patients. Combination therapy has gained popularity in the last two decades, especially in countries with a relatively high gross domestic product. The prevalence of persistent symptoms has also increased; most frequent are complaints about energy levels and fatigue (80% to 90%), weight management (70% to 75%), memory (60% to 80%), and mood (40% to 50%). Pathophysiological explanations for persistent problems are unrealistic patient expectations, comorbidities, somatic symptoms, related disorders (Diagnostic and Statistical Manual of Mental Disorders [DSM-5]), autoimmune neuroinflammation, and low tissue T3. There is fair circumstantial evidence for the latter cause (tissue and specifically brain T3 content is normalized by T4+T3, not by T4 alone), but the other causes are viewed as more relevant in current practice. This might be related to the 'hype' that has emerged surrounding T4+T3 therapy. Although more and better-designed trials are needed to validate the efficacy of T4+T3 combination, the management of persistent symptoms should also be directed towards alternative causes. Improving the doctor-patient relationship and including more and better information is crucial. For example, dissatisfaction with the outcomes of T4 treatment for subclinical hypothyroidism can be anticipated as recent trials have demonstrated that LT4 is hardly effective in improving symptoms associated with subclinical hypothyroidism.

Approach to Obesity in the Older Population

Until recently, weight loss in older obese people was feared because of ensuing muscle loss and frailty. Facing overall increasing longevity, high rates of obesity in older individuals (age ≥ 65 years) and a growing recognition of the health and functional cost of the number of obesity years, abetted by evidence that intentional weight loss in older obese people is safe, this approach is gradually, but not unanimously, being replaced by more active principles. Lifestyle interventions that include reduced but sufficient energy intake, age-adequate protein and micronutrient intake, coupled with aerobic and resistance exercise tailored to personal limitations, can induce weight loss with improvement in frailty indices. Sustained weight loss at this age can prevent or ameliorate diabetes. More active steps are controversial. The use of weight loss medications, particularly glucagon-like peptide-1 analogs (liraglutide as the first example), provides an additional treatment tier. Its safety and cardiovascular health benefits have been convincingly shown in older obese patients with type 2 diabetes mellitus. In our opinion, this option should not be denied to obese individuals with prediabetes or other obesity-related comorbidities based on age. Finally, many reports now provide evidence that bariatric surgery can be safely performed in older people as the last treatment tier. Risk-benefit issues should be considered with extreme care and disclosed to candidates. The selection process requires good presurgical functional status, individualized consideration of the sequels of obesity, and reliance on centers that are highly experienced in the surgical procedure as well as short-term and long-term subsequent comprehensive care and support.

Basal and longitudinal changes in serum levels of TSH in morbid obese patients experiencing failure or success of dietary treatment

PURPOSE

The relationship between thyroid function and obesity is a widely investigated one. The impact of thyroid hormones in determining the outcome of dietary/lifestyle interventions remains to be fully elucidated. The aim of this study was to compare basal and post dietary-intervention circulating thyroid-function parameters, lipid profile and fasting-glucose in euthyroid obese patients according to a success or failure of a dietary intervention program.

METHODS

In a retrospective longitudinal case-control study we enrolled 50 euthyroid obese patients who experienced a success in dietary intervention, as defined by a BMI reduction of at least 5% from baseline (Success Group) and 50 sex and age-matched euthyroid obese patients who experienced failure in dietary intervention as defined by either stable or increased body weight throughout the follow-up (Failure Group). Serum thyroid function parameters and metabolic profile at baseline and at the end of follow-up were collected.

RESULTS

At baseline, the two groups showed similar BMI, total-cholesterol, HDL-cholesterol and fasting-blood-glucose, but patients in Success Group had a significantly higher TSH as compared with Failure Group (2.20 ± 0.97 vs 1.66 ± 0.73, respectively, p < 0.001). Throughout a mean follow-up of 21.4 months TSH significantly decreased in Success Group (2.20 ± 0.97 vs 2.06 ± 0.98; p = 0.029) and increased in Failure Group (1.63 ± 0.72 vs 2.01 ± 0.99; p < 0.001). Multiple regression analysis showed that the outcome of the dietary intervention was significantly and independently related to baseline BMI (0.925; 0.861-0.993), age (0.957; 0.922-0.993), TSH (0.531; 0.290-0.973) and TSH-changes (1.011; 1.000-1.022) during follow-up.

CONCLUSIONS

Baseline serum TSH level is related to the final outcome of a dietary intervention program in obese patients.

LEVEL OF EVIDENCE III

Evidence obtained from a retrospective cohort or case-control analytic studies.

Effects of Childhood Multidisciplinary Care and Growth Hormone Treatment on Health Problems in Adults with Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a complex hypothalamic disorder. Features of PWS include hyperphagia, hypotonia, intellectual disability, and pituitary hormone deficiencies. The combination of growth hormone treatment and multidisciplinary care (GHMDc) has greatly improved the health of children with PWS. Little is known about the effects of childhood GHMDc on health outcomes in adulthood. We retrospectively collected clinical data of 109 adults with PWS. Thirty-nine had received GHMDc during childhood and adolescence (GHMDc+ group) and sixty-three had never received growth hormone treatment (GHt) nor multidisciplinary care (GHMDc− group). Our systematic screening revealed fewer undetected health problems in the GHMDc+ group (10%) than in the GHMDc− group (84%). All health problems revealed in the GHMDc+ group had developed between the last visit to the paediatric and the first visit to the adult clinic and/or did not require treatment. Mean BMI and the prevalence of diabetes mellitus type 2 were significantly lower in the GHMDc+ group compared to the GHMDc− group. As all patients who received GHt were treated in a multidisciplinary setting, it is unknown which effects are the result of GHt and which are the result of multidisciplinary care. However, our data clearly show that the combination of both has beneficial effects. Therefore, we recommend continuing GHMDc after patients with PWS have reached adult age.

Cumulative Effects of Thyroid Hormones Over 10 Years and Risk of General and Abdominal Obesity

We aimed to assess if changes in thyrotropin (TSH) and free thyroxine (FT4) over 10 years of follow-up would be associated with changes in body mass index (BMI) and waist circumference (WC) or risk of obesity. We enrolled 2317 out of 4179 participants in Tehran Thyroid Study with serum TSH between 0.1-10 mU/l and without history of thyroid medication or surgery. Serum concentrations of FT4 and TSH were measured at baseline and three follow-ups (1999-2011). To account for within-subject correlation, the generalized estimating equation was used to assess the association between one standard deviation(SD) change in the main exposures [cumulative excess (CE)TSH and CEFT4] and changes in BMI and WC; calculated scores of CETSH and CEFT4 were included in models as time-varying exposures. Cumulative excess of TSH or FT4 was not associated with increased incidence of general or abdominal obesity. However, CEFT4 was negatively associated with BMI only in overweight and obese subjects. In GEE analysis, one unit increase in TSH was associated with 0.02 kg/m² increase in BMI (95% CI: 0.01, 0.03), which remained significant only in women; although the association was not significant after adding FT4 to model. One unit increase in FT4 was associated with 1.5 kg/m² decrease in BMI (95% CI:-1.8,-1.2) and 4.1 cm decrease in WC (95% CI:-5.1,-3.1) in both sexes independent of TSH and other confounders. Cumulative excess of TSH or FT4 indicated no risk for general or abdominal obesity. However, FT4 was negatively associated with BMI and WC independent of TSH.

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

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

The Relationship Between 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.

Determination of age and sex specific TSH and FT4 reference limits in overweight and obese individuals in an iodine-replete region: Tehran Thyroid Study (TTS)

Introduction: To determine age and sex-specific thyrotropin (TSH) and free thyroxine (FT4) reference ranges according to body mass index (BMI) categories. Methods: With regards to the National Academy of Clinical Biochemistry (NACB) criteria, a total of 2818 individuals from the Tehran Thyroid Study population was selected and categorized in three BMI groups. Results: TSH levels did not differ significantly between BMI groups (p = .054). Females had statistically higher TSH levels than males in all BMI categories (p < .001). According to age-specific analyses, the youngest category (20-29 years) had the highest median values of serum TSH in all BMI groups. With increasing BMI, the 2.5^th percentile of TSH remained approximately unchanged and the 97.5^th percentile showed an increasing pattern. FT4 level was significantly higher in the normal weight group compared to obese individuals (p < .001); females had significantly lower FT4 levels than males in normal weight and obese groups (p < .001). According to age categories, the youngest group (20-29 years) had higher levels of FT4 than the elderly group in all BMI categories. A decreasing pattern in both 2.5^th and 97.5^th percentiles of FT4 was observed along with increasing BMI. Conclusions: Compared to the normal weight population, obese individuals have slightly lower FT4 concentrations accompanied by similar TSH levels. With increasing BMI, upper limits of TSH and FT4 show increasing and decreasing patterns, respectively.

Increased Prolactin is an Adaptive Response to Protect Against Metabolic Disorders in Obesity

OBJECTIVE

Prolactin (PRL) is a polypeptide hormone named for its crucial role in lactation. Recently, PRL has been recognized as a metabolic hormone that regulates energy metabolism. The current study aimed to investigate the relationship between circulating PRL and metabolic alterations in overweight/obese patients and the effect of weight loss through bariatric surgery on circulating PRL.

METHODS

A total of 448 overweight/obese patients aged between 18 and 40 years and 120 age- and sex-matched healthy controls with normal weight were enrolled. Among all participants, 156 obese patients underwent bariatric surgery.

RESULTS

Circulating PRL levels were significantly increased in the overweight (15.27 ± 9.58 μg/L) and obese (17.75 ± 9.15 μg/L) groups compared with the normal weight (13.57 ± 9.03 μg/L) group. Multiple regression analyses demonstrated that the adipose tissue insulin resistance (adipo-IR) level was an independent predictor for PRL (β = -0.451, P < .01). Despite comparable anthropometric parameters, the overweight/obese patients with a higher PRL tertile had decreased levels of triglycerides, nonesterified fatty acids, homeostasis model assessment of insulin resistance, and adipo-IR compared with the patients in the moderate and lower PRL tertiles. Serum PRL levels were significantly decreased following the alleviation of metabolic parameters after bariatric surgery (from 17.12 ± 8.27 to 13.00 ± 5.78 μg/L, P < .05), and the decrease in PRL levels was significantly greater in the lower adipo-IR group than in the higher adipo-IR group (P < .01).

CONCLUSION

An increased serum PRL level might be an adaptive response for protecting against metabolic disorders in obesity.

Correlation between Thyroid Homeostasis and Obesity in Subclinical Hypothyroidism: Community-Based Cross-Sectional Research

OBJECTIVE

It remains unknown whether obesity has an effect on the pituitary-thyroid feedback control axis in subclinical hypothyroidism (SCH). We aimed to investigate the association of thyroid homeostasis with obesity in a SCH population.

METHODS

Our study consisted of a community-based and cross-sectional study from the Epidemiological Survey of Thyroid Diseases in Fujian Province, China. A total of 193 subjects with SCH (90 males and 103 females) without a history of treatment of thyroid disease, such as surgery, radiation, and thyroid hormone or antithyroid medication, were included in the present study. Indices of obesity, including body mass index (BMI), waist circumference (WC), and waist-height ratio (WHtR) were measured.

RESULTS

Our results showed that the secretory capacity of the thyroid gland (SPINA-GT) and Jostel's thyrotropin index (TSHI) were negatively correlated with BMI, WC, and WHtR, whereas the reciprocal of the thyrotroph thyroid hormone resistance index (TTSI-1) was positively correlated with BMI (all p < 0.05). After adjustment for age, sex, smoking, iodine status, and glucolipid metabolism, the associations between TSHI, TTSI (reciprocal transformation), and BMI still persisted (all p < 0.05).

CONCLUSIONS

These results suggest that low levels of thyroid homeostasis indexes may be associated with overall obesity in SCH, rather than central adiposity.

Clinical Parameters Are More Likely to Be Associated with Thyroid Hormone Levels than with Thyrotropin Levels: A Systematic Review and Meta-Analysis

Background: Though the functional states of other endocrine systems are not defined on the basis of levels of controlling hormones, the assessment of thyroid function is based on levels of the controlling hormone thyrotropin (TSH). We, therefore, addressed the question as to whether levels of thyroid hormones [free thyroxine (fT4), total triiodothyronine (TT3)/free triiodothyronine (fT3)], or TSH levels, within and beyond the reference ranges, provide the better guide to the range of clinical parameters associated with thyroid status. Methods: A PubMed/MEDLINE search of studies up to October 2019, examining associations of levels of thyroid hormones and TSH, taken simultaneously in the same individuals, with clinical parameters was performed. We analyzed atrial fibrillation, other cardiac parameters, osteoporosis and fracture, cancer, dementia, frailty, mortality, features of the metabolic syndrome, and pregnancy outcomes. Studies were assessed for quality by using a modified Newcastle-Ottawa score. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed. A meta-analysis of the associations was performed to determine the relative likelihood of fT4, TT3/fT3, and TSH levels that are associated with the clinical parameters. Results: We identified 58 suitable articles and a total of 1880 associations. In general, clinical parameters were associated with thyroid hormone levels significantly more often than with TSH levels-the converse was not true for any of the clinical parameters. In the 1880 considered associations, fT4 levels were significantly associated with clinical parameters in 50% of analyses. The respective frequencies for TT3/fT3 and TSH levels were 53% and 23% (p < 0.0001 for both fT4 and TT3/fT3 vs. TSH). The fT4 and TT3/fT3 levels were comparably associated with clinical parameters (p = 0.71). More sophisticated statistical analyses, however, indicated that the associations with TT3/fT3 were not as robust as the associations with fT4. Conclusions: Thyroid hormones levels, and in particular fT4 levels, seem to have stronger associations with clinical parameters than do TSH levels. Associations of clinical parameters with TSH levels can be explained by the strong negative population correlation between thyroid hormones and TSH. Clinical and research components of thyroidology currently based on the measurement of the thyroid state by reference to TSH levels warrant reconsideration.

Compared with classic Hashimoto's thyroiditis, chronic autoimmune serum-negative thyroiditis requires a lower substitution dose of L-thyroxine to correct hypothyroidism

PURPOSE

Serum-negative-chronic-autoimmune-thyroiditis (SN-CAT) is considered a milder variant of classic Hashimoto's thyroiditis (CHT). However, its prevalence remains unknown and it is still unclear whether SN-CAT behaves differently in terms of L-thyroxine (LT4) substitution treatment of hypothyroidism. Aims of this study were to estimate the prevalence of SN-CAT in a large series of hypothyroid patients and to compare LT4 requirements in hypothyroid patients with SN-CAT and CHT.

METHODS

Five-hundred-eighty-one consecutive patients with primary-autoimmune-hypothyroidism were enrolled in a cross-sectional study. LT4 requirements and thyroid-volume changes were longitudinally evaluated in 49 hypothyroid patients with SN-CAT and in 98 sex and age-matched hypothyroid patients with CHT.

RESULTS

In our series the prevalence of SN-CAT was 20.8%. At diagnosis, patients in the CHT and SN-CAT groups had similar male/female ratio, age and BMI, while serum TSH and thyroid-volume were significantly greater in the CHT group. In the longitudinal study, during a follow-up of 8.9 ± 4.6 years, 8 out of 49 (16.3%) SN-CAT patients developed positive tests for of circulating TPO-Ab and/or Tg-Ab. Thyroid-volume significantly decreased in CHT patients, but not in those with SN-CAT. The maximum daily substitution dose of LT4 was smaller in SN-CAT patients as compared with the CHT ones. Multivariate analysis showed that age, BMI, basal TSH and thyroid antibody status independently and significantly predicted the maximum daily substitution dose of LT4.

CONCLUSIONS

SN-CAT accounts for a significant proportion of patients with autoimmune hypothyroidism. Compared with hypothyroid patients diagnosed with CHT, the SN-CAT ones require smaller doses of LT4 to correct their hypothyroidism.

Agrochemicals and obesity

Obesity has become a very large concern worldwide, reaching pandemic proportions over the past several decades. Lifestyle factors, such as excess caloric intake and decreased physical activity, together with genetic predispositions, are well-known factors related to obesity. There is accumulating evidence suggesting that exposure to some environmental chemicals during critical windows of development may contribute to the rapid increase in the incidence of obesity. Agrochemicals are a class of chemicals extensively used in agriculture, which have been widely detected in human. There is now considerable evidence linking human exposure to agrochemicals with obesity. This review summarizes human epidemiological evidence and experimental animal studies supporting the association between agrochemical exposure and obesity and outlines possible mechanistic underpinnings for this link.

Thyroid Hormone Changes After Sleeve Gastrectomy With and Without Antral Preservation

BACKGROUND

The effect of bariatric surgery on thyroid hormone changes yielded inconsistent results. The aim of the present study was to assess the change of thyroid hormone levels following laparoscopic sleeve gastrectomy (LSG), with or without antral preservation (AP).

METHODS

Thyroid hormones (TSH, FT3, FT4) were examined preoperatively, at the end of the first postoperative month, and first postoperative year. Secondly, antral resection (AR) and AP were compared at inducing weight loss and thereby affecting thyroid hormone levels.

RESULTS

Euthyroid obese patients (86 female/20 male) underwent LSG. Of these, 58 patients underwent AR and 48 patients AP. The mean FT3 levels significantly decreased both in the first postoperative month and the first year (P < 0.001), whereas mean TSH levels decreased significantly in the first postoperative year (P < 0.001). FT4 levels remained nearly unchanged (P = 0.517). Postoperative first year body mass index (BMI) loss, excess BMI loss percentile (%EBMIL), and total body weight loss percentile (%TWL) were significantly higher in AR group than the AP group (P ≤ 0.01). When the change in thyroid hormone levels was analyzed by pyloric distance according to time periods, no significant difference was found in TSH and FT4 levels (P > 0.05); however, reduction in FT3 levels was significantly greater in patients with AR than in AP patients (P = 0.028).

CONCLUSION

LSG promotes significant reduction in TSH and FT3 levels, whereas FT4 levels remain unchanged. LSG with AR provides more weight loss in short term and appears to be more effective at lowering FT3 levels.

Abdominal Obesity Phenotypes and Incidence of Thyroid Autoimmunity: A 9-Year Follow-up

PURPOSE

The association between obesity and autoimmune diseases has been suggested by several previous studies. The objective of our study was to assess the association of abdominal obesity phenotypes with thyroid autoimmunity.

MATERIALS AND METHODS

This study was conducted within the framework of a population-based cohort study, Tehran Thyroid Study (TTS) on 4708 subjects without thyroid autoimmunity at baseline. Participants were categorized into four abdominal obesity phenotypes according to waist circumference (WC) and other metabolic syndrome components. Serum concentrations of thyroid peroxidase antibody (TPOAb), free T4 (FT4), thyrotropin (TSH), glucose, and lipid profiles were measured after 3, 6 and 9 years of follow-up. Cox proportional hazard models were used to evaluate associations of different phenotypes with the incidence of thyroid autoimmunity, adjusted for age, sex, FT4, and TSH.

RESULTS

Highest and lowest incidence rates of TPOAb positivity were observed among metabolically unhealthy, non-abdominally obese (MUNAO) [8.78 (7.31-10.55) per 1000 person-years of follow-up] and metabolically unhealthy abdominally obese (MUAO) [4.98 (3.88-6.41) per 1000 person-years of follow-up] phenotypes. Considering the metabolically healthy non-abdominal obese (MHNAO) individuals as reference, none of metabolically healthy abdominally obese (MHAO), MUNAO, and MUAO phenotypes were associated with increased risk of developing TPOAb positivity. Compared to individuals with high WC, the incidence rate (95%CI) of TPOAb positivity was higher among those with normal WC: 8.44 (7.13-10.0) vs 5.11 (4.01-6.51) per 1000 person-years, respectively. Higher WC was not associated with incident TPOAb positivity.

CONCLUSION

There was no significant association between baseline abdominal obesity phenotype status and development of TPOAb positivity over 9 years of follow-up.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Changes in Thyroid and Glycemic Status and Food Intake in Children with Excess Weight Who Were Submitted for a Multi-Component School Intervention for 16 Months

We investigated if children with excess weight who submitted to two types of intervention at school for 16 months showed improvements in thyroid and glycemic function and food intake. Children (8-11 years) with a body mass index-for-age (BMI/A) of ≥1 Z score were divided into two groups: Treatment 1 (n = 73) involved motivation to adopt healthier lifestyle; Treatment 2 (n = 103) involved performing weekly nutritional education, motivational, and physical activities at school. A semi-quantitative food frequency questionnaire was used. The delta BMI/A were similar after 16 months; Treatment 1 showed higher decrease in thyroid-stimulating hormone (TSH; median (range)): -0.45 (-3.19 to 2.17) and 0.06 (-4.57 to 1.63) mIU/L, p = 0.001), FreeT3 (-0.46 (-2.92 to 1.54) and -0.15 (-2.46 to 1.38) pmol/L, p = 0.038), and FreeT4 -1.41 (-6.18 to 3.47) and -0.90 (-4.89 to 2.96) pmol/L, p = 0.018), followed by decrease in energy intake (7304 (6806 to 7840) and 8267 (7739 to 8832) kJ, Ptreatment = 0.439, Ptime <0.001, interaction group-time p < 0.001), macronutrients and sugar. A positive correlation between FreeT3 and BMI/A, and a negative correlation with FreeT4 and insulin were found at baseline (r 0.212, p < 0.01; r -0.155, p < 0.01, respectively) and follow-up (r 0.222, p < 0.01; r -0.221, p < 0.01). The decrease in overall diet and particularly sugar intake was accompanied by a greater reduction in TSH and FreeT3 in Treatment 1, demonstrating the impact of dietary intake on thyroid function.

The role of thyroid hormone in metabolism and metabolic syndrome

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

Thyroid Nodules in Severely Obese Patients: Frequency and Risk of Malignancy on Ultrasonography

Background: We aimed to compare the thyroid ultrasonographic findings of severely obese versus nonobese individuals, and the frequency, characteristics, and risk of malignancy in detected nodules.Design: Case-control study including 67 adults with severe obesity (body mass index [BMI] ≥ 35 kg/m²) and 67 nonobese controls (BMI < 30 kg/m²). The participants underwent ultrasound evaluation of the thyroid and cervical subcutaneous tissue. The risk of malignancy in detected nodules was determined using the American Thyroid Association (ATA) 2015 and the Thyroid Imaging Reporting and Data System (TI-RADS) classifications. Fine-needle aspiration biopsy (FNAB) was performed in nodules for which the procedure was recommended according to the ATA-2015 or TI-RADS criteria, and the cytological evaluation followed the Bethesda classification.Results: The mean BMI values in the case and control groups were 47.0 ± 6.1 kg/m² and 22.8 ± 2.7 kg/m², respectively. There were no differences between groups regarding sex, age, total T3, and antiperoxidase (antiTPO) antibody positivity. When compared with controls, severely obese individuals showed a greater frequency of parenchymal hypoechogenicity (p = 0.042), cervical subcutaneous tissue thickness (p < 0.001), overall frequency of thyroid nodules (p = 0.038), and frequency of multiple nodules (p = 0.013). No significant differences were observed in terms of risk of nodular malignancy according to both the ATA-2015 and TI-RADS classifications in severely obese compared with nonobese individuals.Conclusions: Severely obese individuals (versus nonobese controls) presented increased parenchymal hypoechogenicity and frequency of thyroid nodules on ultrasonographic evaluation. However, no significant differences were observed in terms of risk of nodular malignancy between both groups according to the ATA-2015 and TI-RADS criteria. Thus, ultrasonographic thyroid screening of severely obese individuals is not justified.

Central Resistance to Thyroid Hormones in Morbidly Obese Subjects Is Reversed after Bariatric Surgery-Induced Weight Loss

Endocrine abnormalities are common in obesity, including altered thyroid function. The altered thyroid function of obesity may be due to a mild acquired resistance to the thyroid hormone. The aim of this study was to investigate the effect of weight loss after bariatric surgery (BS) on resistance to thyroid hormones in patients with extreme obesity compared with a control group. We performed an observational study evaluating patients with extreme obesity who underwent BS. We included 106 patients (83 women) and 38 controls (24 women). The primary endpoint was the thyrotroph thyroxine resistance index (TT4RI) and thyroid stimulating hormone (TSH) index (TSHRI). The parameters were studied before and after surgery. TSHRI and TT4RI were higher in the obese patients than in the control group. TT4RI and TSHI decreased significantly over time after surgery, with this decrease being associated with the excessive body mass index (BMI) loss and C-reactive protein (CRP). In extreme obesity, BS promotes a significant decrease in the increased TT4RI and TSHI. This decrease of TT4RI and TSHI is progressive over time after BS and significantly associated with excess BMI lost and CRP. Extreme obesity is characterized by a mild reversible central resistance to thyroid hormones.

Laparoscopic Sleeve Gastrectomy-Induced Decreases in FT3 and TSH are Related to Fasting C-Peptide in Euthyroid Patients with Obesity

OBJECTIVE

Laparoscopic sleeve gastrectomy (LSG) is one of the most effective therapies to treat obesity. However, whether LSG affects thyroid function remains elusive. Due to a lack of longitudinal research, we explored changes in thyroid function in euthyroid patients with obesity before and after LSG.

METHODS

In total, 109 participants (59 obese patients, 30 normal controls and 20 overweight subjects) were recruited from the Second Xiangya Hospital of Central South University (CSU). All patients underwent LSG, and metabolic indicators and free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) were evaluated at baseline, 6 and 12 months postoperatively.

RESULTS

Compared to the normal control group, the concentrations of FT4 were decreased and TSH were increased in the obese group at baseline. Thyroid hormone levels in all participants were within the normal range during the 12 months after LSG. The concentrations of FT3 (4.83 ± 0.06 vs 5.03 ± 0.08, P = 0.023) and TSH (1.67 ± 0.11 vs 2.25 ± 0.18, P = 0.000) significantly decreased from baseline to 12 months postoperatively, while the concentrations of FT4 significantly increased (17.40 ± 0.52 vs 15.80 ± 0.32, P = 0.004). The decrease in fasting C-peptide (FCP) was related to the decline in FT3 and TSH during 12 months after LSG.

CONCLUSION

Obesity is closely related to thyroid function. LSG promoted a significant decrease in FT3 and TSH and a significant increase in FT4 in euthyroid patients with obesity after LSG. The decline in FCP may be involved in the decrease in FT3 and TSH after LSG.

Prevalence of Hypothyroidism in a Large Sample of Patients with Obesity Hypoventilation Syndrome

PURPOSE

Data on hypothyroidism in patients with obesity hypoventilation syndrome (OHS) are scarce. This study assessed the prevalence of hypothyroidism among a large group of patients with OHS.

PATIENTS AND METHODS

This was a prospective observational study of 308 consecutive patients with OHS seen between January 2002 and December 2018. Serum thyroid-stimulating hormone (TSH) and free-thyroxine (FT4) levels were measured in all patients. The OHS patients were compared with 445 patients with obstructive sleep apnoea (OSA) matched for age, sex, and body mass index (BMI).

RESULTS

The OHS patients had a mean age of 55.1 ± 13.8 years and a BMI of 43.9 ± 14.8 kg/m²; apnoea hypopnea index was ≥30 events/hr in 222 (72%). Clinical hypothyroidism was diagnosed in 58 (18.8%) of the OHS patients; only two cases (0.6%) were diagnosed in the sleep disorders clinic (newly diagnosed cases). Subclinical hypothyroidism was diagnosed in 19 (6.2%) of the OHS patients based on elevated TSH and normal FT4 levels; all cases were newly diagnosed. A logistic regression model identified female sex as the only predictor of clinical hypothyroidism in OHS patients (odds ratio: 2.801 [1.386-5.662], p = 0.004). There was no significant difference in clinical hypothyroidism prevalence between the OHS and OSA patients; however, subclinical hypothyroidism was more common in OHS than in OSA patients (6.2% vs 2.9%, respectively, p = 0.03).

CONCLUSION

Clinical hypothyroidism was prevalent among patients with OHS; however, newly diagnosed cases of clinical hypothyroidism were relatively low. Female sex was the only predictor of clinical hypothyroidism.

The Association of Obesity with Autoimmune Thyroiditis and Thyroid Function-Possible Mechanisms of Bilateral Interaction

A growing number of patients suffer from autoimmune diseases, including autoimmune thyroid disease. There has simultaneously been a significant increase in the prevalence of obesity worldwide. It is still an open question whether adiposity can directly influence activation of inflammatory processes affecting the thyroid in genetically predisposed individuals. Adipokines, biologically active substances derived from the adipocytes, belong to a heterogenic group of compounds involved in numerous physiological functions, including the maintenance of metabolism, hormonal balance, and immune response. Notably, the presence of obesity worsens the course of selected autoimmune diseases and impairs response to treatment. Moreover, the excess of body fat may result in the progression of autoimmune diseases. Nutritional status, body weight, and energy expenditure may influence thyroid hormone secretion. Interestingly, thyroid hormones might influence the activity of adipose tissue as metabolic alterations related to fat tissue are observed under pathological conditions in which there are deficits or overproduction of thyroid hormones. Functioning TSH receptors are expressed on adipocytes. Thermogenesis may presumably be stimulated by TSH binding to its receptor on brown adipocytes. There could be a bilateral interaction between the thyroid and adipose. Obesity may influence the onset and course of autoimmune disease.

Obese Subjects with Non-Alcoholic Fatty Liver Disease Have a Higher Risk of Thyroid Dysfunction

Objectives The effects of obesity on thyroid function have not been well established. The aim of this study was to investigate the effects of body mass index (BMI) and/or non-alcoholic fatty liver disease (NAFLD) on thyroid function. Methods A retrospective longitudinal analysis was conducted among subjects who underwent comprehensive health check-ups at least four times between 2008 and 2017. Thyroid function was investigated according to BMI or presence of NAFLD at the end of follow-up. The subjects were divided into four groups: control (n = 216), subjects with obese (n = 94), subjects with NAFLD (n = 48), and subjects with obese + NAFLD (n = 93). Obesity was defined as BMI ≥ 25 kg/m2. Results During the mean follow-up of 6.8 years (6.8 ± 1.2 years), 42 of the 451 subjects (9.3%) had subclinical hypothyroidism (SCH) but no subjects developed overt hypothyroidism. In multivariate Cox proportional hazard analysis, after adjustment for age, sex, smoking, and baseline thyroid stimulating hormone level, obese subjects with NAFLD had a higher risk of SCH than the control group. Conclusions The obese subjects with NAFLD had a higher risk for SCH in the future.

Thyroid function before and after Roux-en-Y gastric bypass: an observational study

BACKGROUND

Population studies have shown a positive association between thyroid-stimulating hormone (TSH) and body mass index. Recent studies have shown a significant increase in the prevalence of subclinical hypothyroidism (SCH) in obesity. Weight reduction after Roux-en-Y gastric bypass (RYGB) seems to significantly decrease TSH levels.

OBJECTIVES

The purpose of this study was to evaluate the prevalence of SCH in obese patients (class II and III) and to observe the behavior of thyroid hormones (TSH, hormone triiodothyronine, thyroxine, free thyroxine) with significant weight loss after RYGB.

SETTING

Hospital Nossa Senhora das Graças, Curitiba, Paraná, Brazil.

METHODS

We retrospectively reviewed the medical records of 215 obese patients who underwent RYGB between 2005 and 2012 with a follow-up of at least 2 years. The study was observational and descriptive. The selected times for clinical and laboratory evaluations were preoperative, 3, 6, 12, and 24 months after the procedure. Association, correlation, and variance analyses were performed.

RESULTS

The prevalence of SCH preoperatively was 9.3%. SCH was corrected in 89.5% of patients 12 months after RYGB. We did not find an association between TSH and BMI (r = .002, P = .971). There was a positive impact of bariatric surgery on all metabolic variables. We showed that serum TSH level had no positive correlation with the presence or absence of metabolic syndrome.

CONCLUSIONS

Weight loss after bariatric surgery leads to normalization of TSH levels in most patients and none developed overt hypothyroidism. Obese patients with SCH should not be treated with thyroid hormone replacement. Serial monitoring of thyroid function after obesity therapy seems to be a reasonable approach.

The Impact of Obesity on Thyroid Autoimmunity and Dysfunction: A Systematic Review and Meta-Analysis

Background: To help inform decision making in the clinical setting, we carried out a systematic review and meta-analysis to estimate the association of thyroid disease risks with obesity.

Methods: Pubmed, Embase, Web of Science, Cochrane database and Google Scholar electronic databases were searched from inception to October 31, 2018 without language restrictions to explore the relationship between thyroid disorders and obesity. The relative risk (RR) or odds risk (OR) for thyroid disorders were pooled using the SPSS and STATA software.

Results: A total of 22 studies were included in the study. (1) Meta-analysis showed that obesity was significantly associated with an increased risk of hypothyroidism (RR = 1.86, 95% CI 1.63–2.11, P < 0.001). Meta-analyses after stratification further showed that obese population had increased risks of overt hypothyroidism (RR = 3.21, 95% CI 2.12–4.86, P < 0.001) and subclinical hypothyroidism (RR = 1.70, 95% CI 1.42–2.03, P < 0.001). (2) Further meta-analysis also showed obesity was clearly associated with Hashimoto's thyroiditis (RR = 1.91, 95% CI 1.10–3.32, P = 0.022), but not with Graves' disease. (3) In the meta-analysis of antibodies, obesity was correlated with positive thyroid peroxidase antibody (TPOAb) (RR = 1.93, 95% CI 1.31–2.85, P = 0.001), but not with positive thyroglobulin antibody (TGAb).

Conclusions: Obesity was significantly related to hypothyroidism, HT, and TPOAb, implying that prevention of obesity is crucial for thyroid disorders.

Systematic Review Registration: PROSPERO: CRD42018096897.

The Impact of Adiposity and Puberty on Thyroid Function in Children and Adolescents

Background: In the context of a worldwide increase in childhood obesity, euthyroid hyperthyrotropinemia has been consistently reported and raises questions about its etiology, its potential metabolic complications, and its management. In this study we analyze the thyroid function with respect to BMI, pubertal status, and sex in children with obesity and discuss our results on an integrative context with the existent data from the literature. Methods: In this case-control study, we compared 389 children and adolescents with obesity to 158 controls. Age, sex, thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), BMI standard deviation score, and pubertal status were recorded. One factor-analysis of variance (ANOVA) was used with p < 0.05. Results: Mean serum TSH of children with obesity was higher (2.95 ± 1.2 mU/L) compared to normal weight group (2.42 ± 1.43 mU/L) (p < 0.0001). Only in females of both groups, serum TSH, T4, and T3 concentrations were all lower during puberty compared to prepuberty. In prepubertal girls and boys with obesity, a statistically significant correlation between TSH and BMI was found (r = 0.32, p = 0.012 and r = 0.47, p < 0.001, respectively), which is not sustained during puberty. Conclusions: Our results confirm the TSH elevation in children with obesity and indicates that puberty and adiposity have a differential sex-dependent impact on thyroid axis function.

Therapeutic challenges in the application of serum thyroid stimulating hormone testing in the management of patients with hypothyroidism on replacement thyroid hormone therapy: a review

Normalizing serum thyroid stimulating hormone (TSH) levels by lifelong treatment with levothyroxine (LT4) remains the primary goal of therapy for patients with hypothyroidism. The reference ranges for TSH are derived from populations with (supposedly) normal thyroid function. But, TSH results are affected by a number of factors including alterations in TSH levels with age, concurrent illnesses, circadian rhythm, inter- and intra-assay differences, and some commonly used medications that interfere with thyroid function or the TSH test. Furthermore, some patients are complex to manage and bringing serum TSH to within its reference range does not always resolve their symptoms of hypothyroidism. Furthermore, changes in TSH within the reference range may provoke symptoms in some sensitive patients, and others may have a personal "set point" for thyroid hormone levels that represents normal function for that individual, but which is outside the population reference range. The introduction of updated LT4 formulations, with better dosing accuracy and stability compared with older versions, should, in theory at least, provide better stability and accuracy of dosing over time. However, the new LT4 formulations are associated with manifold increases in the number of self-reported adverse events. Therefore, patients with hypothyroidism as well as the clinicians managing them need to better understand the utility as well as the limitations of the widely used TSH measurement. In addition, both pharmaceutical companies and the prescribing clinician need to take greater care when patients are switched from older to newer formulations.