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

Risk Factors for Thyroid Dysfunction in Pregnancy: An Individual Participant Data Meta-Analysis

Background: International guidelines recommend targeted screening to identify gestational thyroid dysfunction. However, currently used risk factors have questionable discriminative ability. We quantified the risk for thyroid function test abnormalities for a subset of risk factors currently used in international guidelines. Methods: We included prospective cohort studies with data on gestational maternal thyroid function and potential risk factors (maternal age, body mass index [BMI], parity, smoking status, pregnancy through in vitro fertilization, twin pregnancy, gestational age, maternal education, and thyroid peroxidase antibody [TPOAb] or thyroglobulin antibody [TgAb] positivity). Exclusion criteria were pre-existing thyroid disease and use of thyroid interfering medication. We analyzed individual participant data using mixed-effects regression models. Primary outcomes were overt and subclinical hypothyroidism and a treatment indication (defined as overt hypothyroidism, subclinical hypothyroidism with thyrotropin >10 mU/L, or subclinical hypothyroidism with TPOAb positivity). Results: The study population comprised 65,559 participants in 25 cohorts. The screening rate in cohorts using risk factors currently recommended (age >30 years, parity ≥2, BMI ≥40) was 58%, with a detection rate for overt and subclinical hypothyroidism of 59%. The absolute risk for overt or subclinical hypothyroidism varied <2% over the full range of age and BMI and for any parity. Receiver operating characteristic curves, fitted using maternal age, BMI, smoking status, parity, and gestational age at blood sampling as explanatory variables, yielded areas under the curve ranging from 0.58 to 0.63 for the primary outcomes. TPOAbs/TgAbs positivity was associated with overt hypothyroidism (approximate risk for antibody negativity 0.1%, isolated TgAb positivity 2.4%, isolated TPOAb positivity 3.8%, combined antibody positivity 7.0%; p < 0.001), subclinical hypothyroidism (risk for antibody negativity 2.2%, isolated TgAb positivity 8.1%, isolated TPOAb positivity 14.2%, combined antibody positivity 20.0%; p < 0.001) and a treatment indication (risk for antibody negativity 0.2%, isolated TgAb positivity 2.2%, isolated TPOAb positivity 3.0%, and combined antibody positivity 5.1%; p < 0.001). Twin pregnancy was associated with a higher risk of overt hyperthyroidism (5.6% vs. 0.7%; p < 0.001). Conclusions: The risk factors assessed in this study had poor predictive ability for detecting thyroid function test abnormalities, questioning their clinical usability for targeted screening. As expected, TPOAb positivity (used as a benchmark) was a relevant risk factor for (subclinical) hypothyroidism. These results provide insights into different risk factors for gestational thyroid dysfunction.

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.

Higher than predicted resting energy expenditure and lower physical activity in healthy underweight Chinese adults

Contrary to popular opinion that lean individuals "eat what they want" and exercise more, Hu et al. study a cohort of healthy underweight volunteers and reveal them to have reduced physical activity relative to normal BMI controls and lower food intake. This cohort is also shown to have higher than expected resting energy expenditure, which is associated with elevations in thyroid hormones.

Subclinical Hypothyroidism in Families Due to Chronic Consumption of Nitrate-Contaminated Water in Rural Areas with Intensive Livestock and Agricultural Practices in Durango, Mexico

Nitrate is a widely disseminated water pollutant and has been linked to health disorders, including hypothyroidism. Here, we evaluated the relationship between thyroid function and chronic exposure to nitrates in rural zone families, in addition to the genetic and autoimmune factors. Exposure and effect biomarkers, thyroid hormones, and autoantibodies of tiroperoxidase were measured, as well the presence of two FOXE1 polymorphisms (rs965513, rs1867277). Pearson’s correlation, principal component analysis, Kruskal–Wallis, and chi-squared tests were used for statistical analysis. A total of 102 individuals were analyzed; 45% presented subclinical hypothyroidism, a negative correlation was observed between methemoglobin and the total T3 (r = −0.43, p = 0.001) and free T3 levels (r = −0.34, p = 0.001), as well as between TSH and the free T4 (r = −0.41, p = 0.0001) and total T4 (r = −0.36, p = 0.0001). A total of 15.7% had positive antithyroid ab-TPO, while the polymorphic genotype (AA) represented only 3% (rs965513) and 4% (rs1867277) among subjects with subclinical hypothyroidism. The high frequency of subclinical hypothyroidism in the population under study could be related, mainly, to chronic exposure through the consumption of nitrate-contaminated water.

Is eNAMPT/visfatin a potential serum marker of papillary thyroid cancer?

PURPOSE

The role of nicotinamide phosphoribosyltransferase (NAMPT)/visfatin in a more aggressive course of many malignancies has been proven. Previous studies have noticed the importance of visfatin in thyroid neoplastic tissue, but the diagnostic and prognostic value of its serum concentration has not been investigated so far. Our study aimed to consider whether extracellular NAMPT (eNAMPT) could be a potential serum marker in recurrent papillary thyroid cancer (PTC).

METHODS

It was a prospective observational study with consecutive enrolment. We recruited 100 patients with PTC after thyroidectomy with postoperative ¹³¹I ablation and 100 healthy controls. Also, 50 randomly selected patients underwent laboratory assessment (including eNAMPT serum concentration by ELISA Assay Kit, TSH, free thyroid hormones, TSH-stimulated thyroglobulin Tg, antibodies - TgAbs, TPOAb) and body composition analysis twice: at admission and 6 months after being on suppressive levothyroxine doses. TSH-stimulated Tg of 1 ng/ml was defined as the cutoff value for predicting disease status as complete remission (n = 55) and recurrent or persistent structural disease (n = 45).

RESULTS

The visfatin serum concentrations in patients diagnosed with PTC and in healthy subjects were not statistically significantly different (p = 0.9425). The eNAMPT levels were also similar in disease-free patients and the ones with tumour relapse. Besides, ROC curve analysis did not detect eNAMPT as a biomarker of PTC.

CONCLUSION

We have not found visfatin as a potential serum marker of papillary thyroid cancer. Also, eNAMPT has no prognostic value in assessing the risk of disease recurrence or metastasis in PTC management.

Association between dietary onion intake and subclinical hypothyroidism in adults: a population-based study from an iodine-replete area

PURPOSE

The protective effect of onion against thyroid hypofunction has been reported in animal studies. However, in humans, the association between onion consumption and subclinical hypothyroidism (SCH) are unclear. The study sought to explore the association between habitual onion intake and SCH among adult population from an iodine-replete area.

METHODS

A cross-sectional study (6515 men and 5290 women) was performed in Tianjin, China. Frequency of onion consumption was assessed using a valid self-administered food frequency questionnaire. Serum free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were determined by chemiluminescence immunoassay. SCH was diagnosed with TSH > 4.78 mIU/L. Multiple logistic regression was used to evaluate the association of onion intake with SCH.

RESULTS

The prevalence of SCH was 2.56% in men and 7.18% in women, respectively. In women, the fully adjusted odds ratios [95% confidence interval (CI)] of having SCH across increasing frequency of onion intake were 1.00 (reference) for <1 time/week, 0.99 (0.73, 1.34) for 1-3 times/week, 0.74 (0.53, 1.03) for 4-6 times/week, and 0.67 (0.47, 0.97) for ≥7 times/week (P for trend <0.01). However, we observed no significant association between onion intake and SCH in men. Stratified analyses suggested a potential effect modification by age: the odds ratios (95% CI) across extreme quartiles was 0.37 (0.17, 0.80) in <40 women and 1.11 (0.51, 2.47) in >60 women.

CONCLUSIONS

Frequent consumption of onion is inversely associated with SCH in adult women from an iodine-replete area. Further studies are needed to explore the casual relationship. TRIAL REGISTRATION WEBSITE: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000031137.

Causal Association Between Serum Thyrotropin and Obesity: A Bidirectional, Mendelian Randomization Study

CONTEXT

The association between serum thyrotropin (TSH) and obesity traits has been investigated previously in several epidemiological studies. However, the underlying causal association has not been established.

OBJECTIVE

This work aimed to determine and analyze the causal association between serum TSH level and obesity-related traits (body mass index [BMI] and obesity).

METHODS

The latest genome-wide association studies (GWASs) on TSH, BMI, and obesity were searched to obtain full statistics. Bidirectional 2-sample mendelian randomization (MR) was performed to explore the causal relationship between serum TSH and BMI and obesity. The inverse variance-weighted (IVW) and MR-Egger methods were used to combine the estimation for each single-nucleotide variation (formerly single-nucleotide polymorphism). Based on the preliminary MR results, free thyroxine (fT4) and free 3,5,3'-triiodothyronine (fT3) levels were also set as outcomes to further analyze the impact of BMI on them. BMI and obesity were treated as the outcomes to evaluate the effect of serum TSH on them, and TSH was set as the outcome to estimate the effect of BMI and obesity on it.

RESULTS

IVW and MR-Egger results both indicated that genetically driven serum TSH did not causally lead to changes in BMI or obesity. Moreover, the IVW method showed that the TSH level could be significantly elevated by genetically predicted high BMI (β = .038, SE = 0.013, P = .004). In further MR analysis, the IVW method indicated that BMI could causally increase the fT3 (β = 10.123, SE = 2.523, P < .001) while not significantly affecting the fT4 level.

CONCLUSION

Together with fT3, TSH can be significantly elevated by an increase in genetically driven BMI.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

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

Central vs. Peripheral Action of Thyroid Hormone in Adaptive Thermogenesis: A Burning Topic

Thyroid hormones (TH) contribute to the control of adaptive thermogenesis, which is associated with both higher energy expenditure and lower body mass index. While it was clearly established that TH act directly in the target tissues to fulfill its metabolic activities, some studies have rather suggested that TH act in the hypothalamus to control these processes. This paradigm shift has subjected the topic to intense debates. This review aims to recapitulate how TH control adaptive thermogenesis and to what extent the brain is involved in this process. This is of crucial importance for the design of new pharmacological agents that would take advantage of the TH metabolic properties.

Association of serum uric acid with thyroid function in health check-up participants

Background

The relationship of uric acid (UA) with the thyroid function among healthy individuals remains unclear. We aimed to examine the relationship between UA contents and thyroid hormone levels in healthy Chinese individuals.

Methods

This was a cross-sectional study of 1186 Chinese adults (736 men and 450 women) who underwent a health check-up at the Huadong Hospital Affiliated to Fudan University (Shanghai, China) between January 1, 2010 and July 31, 2018. Clinical and thyroid hormone levels were compared in different UA groups (in male and menopause women groups, MG1: UA < 5 mg/dL; MG2: 5 mg/dL ≤ UA< 7 mg/dL; and MG3: UA ≥ 7 mg/dL; in female groups, FG1 to FG3 represent the UA levels of <4 mg/dL, 4 mg/dL ≤ UA< 6 mg/dL, and ≥6 mg/dL, respectively). In addition, natural cubic spline regression, together with Pearson correlation analysis, was performed in investigating the correlation of UA with thyroid hormones.

Results

After adjusting for confounding factors, low levels of UA (for males, UA < 5.30 mg/dL; for females, UA < 4.05 mg/dL) were negatively correlated with free triiodothyronine (FT3) both in men and women. UA levels between 4.83 and 6.06 mg/dL may act to protect FT3 in women, while UA levels between 6.39 and 7.09 mg/dL may protect FT3 in men. FT3 levels of low-range UA group reduced compared with mid-range UA and the high-range UA groups in both men and women.

Conclusions

Our results provide epidemiologic evidence to support the negative correlation between low UA contents and FT3 in the Chinese Han population, suggesting that the reduced UA contents may serve as the risk factor to predict poor thyroid function in Chinese individuals.

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.

Insulin Resistance in Association with Thyroid Function, Psychoemotional State, and Cardiovascular Risk Factors

Background: Individuals with insulin resistance (IR) have a high risk of diabetes or metabolic syndrome, and they are more likely to have depression. Furthermore, IR by itself is a major cardiovascular risk factor in healthy persons. Thus, we aimed to investigate IR in association with thyroid function, psychoemotional state, and cardiovascular risk factors among 45–84-year-old citizens of Palanga. Methods: A randomized epidemiological study was performed with 850 subjects. All participants were evaluated for sociodemographic, clinical, and cardiovascular risk factors and biochemical analysis. IR was evaluated by the homeostasis model assessment of IR (HOMA-IR). Results: All study participants were stratified into groups without IR (HOMA-IR ≤ 2.7) and with IR (HOMA-IR > 2.7). The analysis of parameters between the two study groups showed some statistically significant relationships between IR and cardiovascular risk factors. The predictable accuracy was presented using receiver performance characteristic curves for HOMA-IR scores in women and men separately. If the HOMA-IR score is higher than 3.45, individuals are significantly more likely to have type 2 diabetes mellitus (T2DM). Conclusions: An increase of fasting glucose and more frequent incidence of metabolic syndrome, diabetes, and cardiovascular diseases in subjects with IR are associated with the prevalence of cardiovascular risk factors. There was no significant association between thyroid function and HOMA-IR. HOMA-IR cut-offs could predict the presence of T2DM.

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.

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

Background

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

Methods and findings

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

Conclusions

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

The Association 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.

Thyroid disease and the metabolic syndrome

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Association between thyroid hormone levels, body composition and insulin resistance in euthyroid subjects with normal thyroid ultrasound: The Kangbuk Samsung Health Study

OBJECTIVE

Thyroid hormones play crucial roles in the control of energy homoeostasis and can influence body composition. In contrast, the changes in body composition might influence thyroid hormone levels. We evaluated associations between thyroid hormone levels, body composition and insulin resistance in euthyroid subjects with normal thyroid ultrasound (US) findings.

DESIGN AND PATIENTS

This retrospective cross-sectional study included 36 655 euthyroid subjects who joined the medical health check-up programme at our institution. Serum thyroid hormone levels were analysed in association with body fat percentage (BFP), skeletal muscle mass index (SMI) and homoeostatic model assessment of insulin resistance (HOMA-IR). Linear regression analyses were performed to evaluate relationships between thyroid hormone levels and anthropometric parameters.

RESULTS

Mean age was 36.4 years, and 49% of subjects were female. In multiple linear regression analysis, serum-free triiodothyronine (FT3) levels exhibited positive associations with waist circumference (WC) and HOMA-IR and a negative association with body weight, body mass index (BMI) and SMI among both men and women. The association between serum-free thyroxine (FT4) levels and anthropometric markers showed inconsistent results in men and women. Serum thyroid-stimulating hormone (TSH) levels showed a positive association with HOMA-IR in both men and women.

CONCLUSIONS

Lower SMI was significantly associated with higher serum FT3 levels, the active form of thyroid hormone, in both men and women. Higher insulin resistance was positively associated with serum FT3 levels and inversely associated with serum TSH levels in euthyroid subjects with normal thyroid US findings.

Tehran Thyroid Study (TTS)

CONTEXT

This review summarizes key findings of the Tehran thyroid study (TTS), a large scale community-based study with approximately a two decade follow-up, about the incidence, prevalence, and natural course of thyroid disorders as well as associations between thyroid diseases and metabolic syndrome (MetS), dysglycemia, and cardiovascular disease (CVD).

EVIDENCE ACQUISITION

PubMed, Scopus, and Web of Science databases, and the library of Research Institute for Endocrine Sciences were used to search for TTS articles. Articles were subdivided based on the fields of prevalence, incidence and natural course, and associations of thyroid function with the incident hypertension (HTN), MetS and CVDs.

RESULTS

The 2.5th and 97.5th percentiles of serum thyrotropin (TSH) were 0.32 and 5.06 mU/L, respectively. Estimated reference intervals (2.5th and 97.5th percentiles) for thyroid peroxidase antibody (TPOAb) levels were 1.5 - 32.8 and 2.1 - 35 IU/mL in men and women, respectively. Euthyroid persistency was 93.24% during 6 years. There was a negative association between free thyroxine (FT4) levels and insulin resistance. Decreasing FT4 values over time would predict MetS in euthyroid and subclinical hypothyroid subjects (TSH < 10 mU/L). The incidence of thyroid disorders in patients with diabetes, pre-diabetes and healthy controls was 14, 18, and 21 per 1000 person-years, respectively, indicating significantly lower incidence in individuals with diabetes compared to healthy controls. Serum FT4 within the reference range was positively associated with all blood pressure (BP) measures in the total population and in men; however, serum TSH was positively associated with only systolic BP (SBP), diastolic BP (DBP) and mean arterial pressure of men. No associations were found between various states of thyroid function and prevalence and incidence of CVD.

CONCLUSIONS

A well designed cohort study aimed to investigate the gap in knowledge regarding thyroid disorders can generate many hypotheses to be examined in randomized controlled trials.

Integrating Thyroid Hormone Signaling in Hypothalamic Control of Metabolism: Crosstalk Between Nuclear Receptors

The obesity epidemic is well recognized as a significant global health issue. A better understanding of the energy homeostasis mechanisms could help to identify promising anti-obesity therapeutic strategies. It is well established that the hypothalamus plays a pivotal role governing energy balance. The hypothalamus consists of tightly interconnected and specialized neurons that permit the sensing and integration of several peripheral inputs, including metabolic and hormonal signals for an appropriate physiological response. Current evidence shows that thyroid hormones (THs) constitute one of the key endocrine factors governing the regulation and the integration of metabolic homeostasis at the hypothalamic level. THs modulate numerous genes involved in the central control of metabolism, as TRH (Thyrotropin-Releasing Hormone) and MC4R (Melanocortin 4 Receptor). THs act through their interaction with thyroid hormone receptors (TRs). Interestingly, TH signaling, especially regarding metabolic regulations, involves TRs crosstalk with other metabolically linked nuclear receptors (NRs) including PPAR (Peroxisome proliferator-activated receptor) and LXR (Liver X receptor). In this review, we will summarize current knowledge on the important role of THs integration of metabolic pathways in the central regulation of metabolism. Particularly, we will shed light on the crosstalk between TRs and other NRs in controlling energy homeostasis. This could be an important track for the development of attractive therapeutic compounds.

Association Between Thyroid Function and Development of Different Obesity Phenotypes in Euthyroid Adults: A Nine-Year Follow-Up

BACKGROUND

Considering inconsistent and conflicting data on associations of thyroid function, within the reference range, with anthropometric measures and metabolic syndrome, this study aimed to investigate the relationship between thyroid function and different obesity phenotypes over nine years of follow-up.

METHODS

This study was conducted on 1938 individuals from an ongoing population-based cohort study, the Tehran Thyroid Study. Participants were categorized into four obesity phenotypes based on body mass index and metabolic status. To investigate the associations of thyrotropin and free thyroxine (fT4) with incidence of different obesity phenotypes across the study period, a multivariate approach based on a generalized estimating equation method was used.

RESULTS

At baseline, individuals with the metabolically healthy normal weight (MHNW) phenotype had higher serum fT4 levels (1.2 ± 0.16 ng/dL vs. 1.14 ± 0.14 ng/dL, 1.16 ± 0.14 ng/dL, and 1.17 ± 0.15 ng/dL in metabolically healthy obese [MHO], metabolically unhealthy normal weight, and metabolically unhealthy obese individuals, respectively). The results of the generalized estimating equation analysis after multivariate adjustment for age, sex, smoking, physical activity, education level, thyroid peroxidase antibody status, and homeostasis model assessment-insulin resistance showed that each 1 ng/dL increment in fT4 levels within the reference range was accompanied with a 1.65-fold [confidence interval (CI) 1.09-2.5] increase of developing the MHNW phenotype during 9.2 years of follow-up. Moreover, each 1.0 ng/dL increment in fT4 within the reference range was associated with a 50% decreased risk of developing the MHO phenotype (odds ratio = 0.50 [CI 0.32-0.76]). Meanwhile, a significant positive association was found between serum thyrotropin levels and development of the metabolically unhealthy normal weight phenotype (odds ratio = 1.22 [CI 1.01-1.48]).

CONCLUSIONS

Serum fT4 concentrations within the reference range are associated with the development of some obesity phenotypes, including the MHNW and MHO phenotypes, after consideration of potential confounders.

Iodine deficiency in pregnancy: Still a health issue for the women of Cassino city, Italy

OBJECTIVE

The World Health Organization, the United Nations Children's Fund, and the International Council for the Control of Iodine Deficiency Disorders recommend a median urinary iodine concentration (UIC) in pregnant women between 150 µg/L and 249 µg/L. In the present study, we evaluated whether in the urban area of Cassino (central Italy), after a national salt iodination program (30 mg/kg) was introduced in 2005, the increased demand of iodine during pregnancy was satisfied.

METHODS

Between January 2016 and April 2017, 99 pregnant women were enrolled to evaluate UIC in spot urine samples, serum level of thyrotropin, free thyroxine, antithyroglobulin and antithyroperoxidase autoantibodies, and thyroid volume by ultrasonography. Eighty clinically healthy non-pregnant women were evaluated as controls.

RESULTS

The median UIC was of 97.7 µg/L and 110.3 µg/L, respectively, in control and pregnant women. A significant increase (P < 0.001) of median thyroid volume was found in pregnant women, relative to control women, being, respectively, 10.4 mL (range 3.68-19.49 mL) and 7.16 mL (range 2.57-14.00 mL). A positive correlation was found between thyroid volume and anthropometric parameters, and an inverse correlation was identified between free thyroxine serum levels and anthropometric parameters.

CONCLUSIONS

This observational study found that the majority of pregnant women and their fetuses appear not to be protected from the detrimental consequences of iodine deficiency. Therefore, the identification of new strategies to increase the knowledge and awareness of the general population regarding the beneficial effects of iodine supplementation during pregnancy is highly required.