Thyrotropin Levels, Insulin Resistance, and Metabolic Syndrome: A Cross-Sectional Analysis in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Association between the triglyceride-glucose index and thyroid disorders: a cross-sectional survey and Mendelian randomization analysis

BACKGROUND

Metabolic diseases are associated with thyroid disorders. Insulin resistance is the common pathological basis of metabolic diseases. We explored the relationship between the triglyceride-glucose (TyG) index, a simple insulin-resistance marker, and thyroid disorders.

METHODS

Eligible TIDE (Thyroid Diseases, Iodine Status and Diabetes Epidemiology) subjects (n = 47,710) were screened with inclusion/exclusion criteria. Thyroid disorder prevalence among different TyG index groups was stratified by sex. Logistic regression evaluated the correlation between the TyG index and thyroid disorders. Multiple linear regression evaluated the association between the TyG index and TSH. Additionally, two-sample Mendelian randomization (MR) using published genome-wide association study data evaluated causality in the association between the TyG index and TSH.

RESULTS

Men and women with greater TyG indices had a significantly greater prevalence of thyroid disorders than individuals with the lowest quartile (Q1) of TyG index (p < 0.05). Following adjustment for confounding factors, we observed that a greater TyG index significantly increased the risk of subclinical hypothyroidism in men and women (men: Q2: odds ratio (OR) [95% confidence interval (CI)] = 1.22 [1.07-1.38], p = 0.002; Q3: OR [95% CI] = 1.28 [1.12-1.45], p < 0.001; Q4: OR [95% CI] = 1.29 [1.12-1.50], p = 0.001; women: Q2: OR [95% CI] = 1.25 [1.12-1.39], p < 0.001; Q3: OR [95% CI] = 1.47 [1.31-1.64], p < 0.001; Q4: OR [95% CI] = 1.61 [1.43-1.82], p < 0.001). Only among women was the highest TyG index quartile associated with hypothyroidism (OR [95% CI] = 1.70 [1.15-2.50], p = 0.007). Additionally, in men, the association exists only in the more than adequate iodine intake population. In women, the relationship between the TyG index and thyroid disorders disappears after menopause. Furthermore, the TyG index exhibited a linear positive correlation with TSH levels. The MR analysis results revealed a causal relationship between a genetically determined greater TyG index and increased TSH (inverse-variance weighting (IVW): OR [95% CI] = 1.14 [1.02-1.28], p = 0.020); however, this causal relationship disappeared after adjusting for BMI in multivariable MR (MVMR) analysis (MVMR-IVW: OR 1.03, 95% CI 0.87-1.22, p = 0.739).

CONCLUSIONS

A greater TyG index is associated with hypothyroidism and subclinical hypothyroidism and varies by sex and menopausal status. MR analysis demonstrated that the causal relationship between a genetically determined greater TyG index and elevated TSH levels is confounded or mediated by BMI.

A systematic review and meta-analysis investigating the relationship between metabolic syndrome and the incidence of thyroid diseases

PURPOSE

To assess the prospective association between metabolic syndrome (MetS), its components, and incidence of thyroid disorders by conducting a systematic review and meta-analysis.

METHODS

A systematic search was performed in Ovid Medline, Embase.com, and Cochrane CENTRAL from inception to February 22, 2023. Publications from prospective studies were included if they provided data on baseline MetS status or one of its components and assessed the incidence of thyroid disorders over time. A random effects meta-analysis was conducted to calculate the odds ratio (OR) for developing thyroid disorders.

RESULTS

After full-text screening of 2927 articles, seven studies met our inclusion criteria. Two of these studies assessed MetS as an exposure (N = 71,727) and were included in our meta-analysis. The association between MetS at baseline and incidence of overt hypothyroidism at follow-up yielded an OR of 0.78 (95% confidence interval [CI]: 0.52-1.16 for two studies, I2 = 0%). Pooled analysis was not possible for subclinical hypothyroidism, due to large heterogeneity (I2 = 92.3%), nor for hyperthyroidism, as only one study assessed this association. We found evidence of an increased risk of overt (RR: 3.10 (1.56-4.64, I2 = 0%) and subclinical hypothyroidism (RR 1.50 (1.05-1.94), I2 = 0%) in individuals with obesity at baseline. There was a lower odds of developing overt hyperthyroidism in individuals with prediabetes at baseline (OR: 0.68 (0.47-0.98), I2 = 0%).

CONCLUSIONS

We were unable to draw firm conclusions regarding the association between MetS and the incidence of thyroid disorders due to the limited number of available studies and the presence of important heterogeneity in reporting results. However, we did find an association between obesity at baseline and incidence of overt and subclinical hypothyroidism.

Accumulative prediction values of serum thyroid stimulating hormone and visceral adipose tissue for metabolic syndrome in postmenopausal women: A 10-year follow-up study of Chinese population

AIMS

We aim to explore the cumulative predictive value of elevated serum thyroid stimulating hormone (TSH) and visceral fat area (VFA) for metabolic syndrome (MS) development in postmenopausal women.

METHODS

A total of 1006 postmenopausal females were enrolled in a 10-year prospective longitudinal study from 2011 to 2021 in the community of Banknote Printing Company of Chengdu. The sociodemographic information collection and anthropometric measurements were made by a professional nurse. Fasting blood samples were drawn for chemical analysis of fasting plasma glucose, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and TSH. Magnetic resonance imaging was performed to measure VFA. All the participants were categorized into four groups according to median VFA and serum level of TSH.

RESULTS

A total of 793 postmenopausal females without MS underwent a 10-year follow-up study grouping by TSH and VFA: Group 1 (TSH level <4.2 μIU/mL, and VFA < 70 cm2 ), Group 2 (TSH level ≥4.2 μIU/mL, and VFA < 70 cm2 ), Group 3 (TSH level <4.2 μIU/mL, and VFA ≥70 cm2 ) and Group 4 (TSH level ≥4.2 μIU/mL, and VFA ≥70 cm2 ). During the 10-year follow-up, MS was newly developed in 326 (41.1%) subjects. The incidence of MS was 29.8% (n = 53), 35.2% (n = 63), 41% (n = 87), and 55% (n = 123) from Group 1 to Group 4 (Group 4 vs other groups, p < .001). Cox regression analysis for MS prediction demonstrated that both TSH (Model 3, hazard ratio [HR] = 1.07 [95% confidence interval, 1.05-1.09]) and VFA (Model 4, HR = 1.02 [95% confidence interval, 1.01-1.08]) were not only independent predictors of MS but also involved some interaction between each other (p for interaction = .021).

CONCLUSION

Our findings suggested that mutual interaction between higher TSH and VFA contributed to the development of MS. Further studies are needed to clarify these contributions.

Subclinical thyroid dysfunction and incident diabetes: a systematic review and an individual participant data analysis of prospective cohort studies

OBJECTIVE

Few prospective studies have assessed whether individuals with subclinical thyroid dysfunction are more likely to develop diabetes, with conflicting results. In this study, we conducted a systematic review of the literature and an individual participant data analysis of multiple prospective cohorts to investigate the association between subclinical thyroid dysfunction and incident diabetes.

METHODS

We performed a systematic review of the literature in Medline, Embase, and the Cochrane Library from inception to February 11, 2022. A two-stage individual participant data analysis was conducted to compare participants with subclinical hypothyroidism and subclinical hyperthyroidism vs euthyroidism at baseline and the adjusted risk of developing diabetes at follow-up.

RESULTS

Among 61 178 adults from 18 studies, 49% were females, mean age was 58 years, and mean follow-up time was 8.2 years. At the last available follow-up, there was no association between subclinical hypothyroidism and incidence of diabetes (odds ratio (OR) = 1.02, 95% CI: 0.88-1.17, I2 = 0%) or subclinical hyperthyroidism and incidence of diabetes (OR = 1.03, 95% CI: 0.82-1.30, I2 = 0%), in age- and sex-adjusted analyses. Time-to-event analysis showed similar results (hazard ratio for subclinical hypothyroidism: 0.98, 95% CI: 0.87-1.11; hazard ratio for subclinical hyperthyroidism: 1.07, 95% CI: 0.88-1.29). The results were robust in all sub-group and sensitivity analyses.

CONCLUSIONS

This is the largest systematic review and individual participant data analysis to date investigating the prospective association between subclinical thyroid dysfunction and diabetes. We did not find an association between subclinical thyroid dysfunction and incident diabetes. Our results do not support screening patients with subclinical thyroid dysfunction for diabetes.

SIGNIFICANCE STATEMENT

Evidence is conflicting regarding whether an association exists between subclinical thyroid dysfunction and incident diabetes. We therefore aimed to investigate whether individuals with subclinical thyroid dysfunction are more prone to develop diabetes in the long run as compared to euthyroid individuals. We included data from 18 international cohort studies with 61 178 adults and a mean follow-up time of 8.2 years. We did not find an association between subclinical hypothyroidism or subclinical hyperthyroidism at baseline and incident diabetes at follow-up. Our results have clinical implications as they neither support screening patients with subclinical thyroid dysfunction for diabetes nor treating them in the hope of preventing diabetes in the future.

Heart Disease and Stroke Statistics-2021 Update: A Report From the American Heart Association

BACKGROUND

The American Heart Association, in conjunction with the National Institutes of Health, annually reports the most up-to-date statistics related to heart disease, stroke, and cardiovascular risk factors, including core health behaviors (smoking, physical activity, diet, and weight) and health factors (cholesterol, blood pressure, and glucose control) that contribute to cardiovascular health. The Statistical Update presents the latest data on a range of major clinical heart and circulatory disease conditions (including stroke, congenital heart disease, rhythm disorders, subclinical atherosclerosis, coronary heart disease, heart failure, valvular disease, venous disease, and peripheral artery disease) and the associated outcomes (including quality of care, procedures, and economic costs).

METHODS

The American Heart Association, through its Statistics Committee, continuously monitors and evaluates sources of data on heart disease and stroke in the United States to provide the most current information available in the annual Statistical Update. The 2021 Statistical Update is the product of a full year's worth of effort by dedicated volunteer clinicians and scientists, committed government professionals, and American Heart Association staff members. This year's edition includes data on the monitoring and benefits of cardiovascular health in the population, an enhanced focus on social determinants of health, adverse pregnancy outcomes, vascular contributions to brain health, the global burden of cardiovascular disease, and further evidence-based approaches to changing behaviors related to cardiovascular disease.

RESULTS

Each of the 27 chapters in the Statistical Update focuses on a different topic related to heart disease and stroke statistics.

CONCLUSIONS

The Statistical Update represents a critical resource for the lay public, policy makers, media professionals, clinicians, health care administrators, researchers, health advocates, and others seeking the best available data on these factors and conditions.

The Relationship Between Thyroid Function and Metabolic Syndrome and Its Components: A Cross-Sectional Study in a Chinese Population

OBJECTIVE

The present study examined the relationship between thyroid function status and the prevalence of metabolic syndrome in a Chinese population.

METHODS

Cross-sectional data were obtained from the Thyroid Disease, Iodine Nutrition and Diabetes Epidemiology (TIDE) Survey. A total of 62,408 subjects aged ≥18 years were enrolled. Differences in metabolic indicators and the prevalence of metabolic syndrome according to sex and thyroid function status were compared. Logistic regression was used to analyze the influence of thyroid function on metabolic syndrome and its components.

RESULTS

The prevalence of metabolic syndrome was generally higher in men than women. Overt hyperthyroidism and subclinical hypothyroidism had a significant effect on metabolism in men. Body mass index (BMI), waist circumference, and triglycerides (TGs) were significantly lower in men in the overt hyperthyroidism group, and BMI, waist circumference, systolic blood pressure (SBP) and TGs were higher in men in the subclinical hypothyroidism group than men in the normal group. Overt and subclinical hypothyroidism had significant impacts on metabolic components in women. BMI, waist circumference, TGs, SBP and DBP in the subclinical and overt hypothyroidism groups were significantly higher than the euthyroid group in women. The relative risk of abdominal obesity and hypertriglyceridemia was increased in women with hypothyroidism. Thyroid dysfunction had different effects on metabolic syndrome and its components before and after menopause.

CONCLUSION

Thyroid function had important effects on the prevalence of metabolic syndrome. Women with hypothyroidism, especially post-menopausal women, had a higher risk of metabolic syndrome than men.

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.

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.

Heart Disease and Stroke Statistics-2020 Update: A Report From the American Heart Association

BACKGROUND

The American Heart Association, in conjunction with the National Institutes of Health, annually reports on the most up-to-date statistics related to heart disease, stroke, and cardiovascular risk factors, including core health behaviors (smoking, physical activity, diet, and weight) and health factors (cholesterol, blood pressure, and glucose control) that contribute to cardiovascular health. The Statistical Update presents the latest data on a range of major clinical heart and circulatory disease conditions (including stroke, congenital heart disease, rhythm disorders, subclinical atherosclerosis, coronary heart disease, heart failure, valvular disease, venous disease, and peripheral artery disease) and the associated outcomes (including quality of care, procedures, and economic costs).

METHODS

The American Heart Association, through its Statistics Committee, continuously monitors and evaluates sources of data on heart disease and stroke in the United States to provide the most current information available in the annual Statistical Update. The 2020 Statistical Update is the product of a full year's worth of effort by dedicated volunteer clinicians and scientists, committed government professionals, and American Heart Association staff members. This year's edition includes data on the monitoring and benefits of cardiovascular health in the population, metrics to assess and monitor healthy diets, an enhanced focus on social determinants of health, a focus on the global burden of cardiovascular disease, and further evidence-based approaches to changing behaviors, implementation strategies, and implications of the American Heart Association's 2020 Impact Goals.

RESULTS

Each of the 26 chapters in the Statistical Update focuses on a different topic related to heart disease and stroke statistics.

CONCLUSIONS

The Statistical Update represents a critical resource for the lay public, policy makers, media professionals, clinicians, healthcare administrators, researchers, health advocates, and others seeking the best available data on these factors and conditions.

The Association Between Serum Thyrotropin Within the Reference Range and Metabolic Syndrome in a Community-Based Chinese Population

PURPOSE

We aimed to ascertain the association between thyrotropin (TSH) levels in euthyroid state and the prevalence of metabolic syndrome (MetS) in a community-based Chinese population.

PARTICIPANTS AND METHODS

Based on a large and well-characterized community cohort in Beijing, China, 1831 men and 1742 women with serum TSH levels within the reference range (0.50-4.78 µIU/mL) were stratified by quartiles of TSH (Q1-4). MetS was identified according to the criteria of International Diabetes Federation guidelines. Poisson regression models were used to estimate the association between serum TSH and the prevalence of MetS and its components before and after adjustment for potential confounding factors. The reported association was measured using the prevalence ratio (PR) with its respective 95% confidence interval (95% CI).

RESULTS

The prevalence of MetS in euthyroid population across TSH quartiles (Q1-4) was 38.9%, 44.6%, 41.0%, and 47.7%, respectively, in men (P = 0.045), and 47.7%, 46.6%, 46.9%, and 54.6%, respectively, in women (P = 0.032). Compared with the reference group TSH-Q1, the prevalence of MetS was higher among TSH-Q4 group both in men (PR = 1.27; 95% CI: 1.09, 1.48, P = 0.002) and women (PR = 1.21; 95% CI: 1.07, 1.37, P = 0.003) even after adjustment for age, lifestyle factors, serum levels of free triiodothyronine (FT3), and free thyroxine (FT4). Most of the components of MetS were common in higher serum TSH levels within the normal range.

CONCLUSION

The prevalence of MetS and most of its components increased in the higher TSH group in euthyroid Chinese population.

The Relationship between Thyroid Function and Different Obesity Phenotypes in Korean Euthyroid Adults

BACKGROUND

Thyroid disease and metabolic syndrome are both associated with cardiovascular disease. The aim of this study was to investigate the correlation between thyroid hormones and obesity sub-phenotypes using nationwide data from Korea, a country known to be iodine replete.

METHODS

This study was based on data obtained from the sixth Korea National Health and Nutrition Examination Survey, administered from 2013 to 2015. A total of 13,873 participants aged ≥19 years were included, and classified into four groups: metabolically healthy non-obesity (MHNO), metabolically healthy obesity (MHO), metabolically unhealthy non-obesity (MUNO), and metabolically unhealthy obesity (MUO) by body fat on the basis of body mass index and metabolic health.

RESULTS

At baseline, serum free thyroxine (fT4) values were significantly higher in the MHNO phenotype (MHNO, 1.27±0.01 ng/dL; MHO, 1.25±0.01 ng/dL; MUNO, 1.24±0.01 ng/dL; MUO, 1.24±0.01 ng/dL, P<0.001) in total study population. However, this significant association no longer remained after adjustment for age, urine iodine concentration, and smoking (P=0.085). After adjustment for confounders, statistically significant association was observed between lower thyroid stimulating hormone (TSH) and MHNO phenotype (P=0.044). In men participants (not women), higher fT4 values were significantly associated with MHNO phenotype (P<0.001). However, no significant association was observed between thyroid function (TSH or fT4) and obesity phenotypes in groups classified by age (cutoff age of 55 years).

CONCLUSION

Although there was a difference by age and sex, we found that the decrease of TSH and the increase of fT4 values were associated with MHNO.

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.

In thyroxine-replaced hypothyroid postmenopausal women under simultaneous calcium supplementation, switch to oral liquid or softgel capsule L-thyroxine ensures lower serum TSH levels and favorable effects on blood pressure, total cholesterolemia and glycemia

PURPOSE

In postmenopausal women under L-T4 therapy, which was subsequently accompanied by calcium carbonate (CC) supplementation taken 6-8 h after tablet L-T4, TSH levels were greater than prior to adding CC. Total cholesterolemia [CHOL], fasting glycemia [FG], systolic and diastolic blood pressure [SBP, DBP] were also greater than baseline. Our aim was to explore the effects of either liquid or softgel capsule L-T4, while maintaining CC ingestion 6-8 h, later on TSH levels, CHOL, FG, SBP, and DBP.

METHODS

We proposed to 50 hypothyroid postmenopausal women under tablet L-T4 therapy, to switch to either liquid or softgel capsule L-T4 at the same daily dose while maintaining CC ingestion 6-8 h later. Sixteen women accepted [group I; liquid (n = 9), capsule (n = 7)], while 34 continued tablet L-T4 [group II, (n = 34)].

RESULTS

After 3 months, in group I, TSH decreased significantly (1.23 ± 0.49 vs. 1.80 ± 0.37 mU/L, P < 0.01), as did FG (80.7 ± 7.9 vs. 83.4 ± 6.3 mg/dL, P < 0.05); CHOL, SBP, and DBP decreased, though insignificantly. In contrast, in group II, TSH, FG, CHOL, SBP increased insignificantly, and DBP increased borderline significantly (69.7 ± 9 vs. 66.3 ± 6.5, P < 0.10). Compared to baseline (before adding CC), in group I, TSH was significantly lower (P < 0.01) and the other indices similar; in group II, TSH, FG, and SBP were significantly higher (P < 0.05), DBP borderline significantly higher (P < 0.10) and CHOL insignificantly higher. Performance of liquid L-T4 and capsule L-T4 was similar.

CONCLUSION

Delaying CC ingestion even by 6-8 h after taking tablet L-T4 is not entirely satisfactory, unlike liquid or softgel L-T4.

L-thyroxine malabsorption due to calcium carbonate impairs blood pressure, total cholesterolemia, and fasting glycemia

PURPOSE

Calcium carbonate was previously shown to interfere with L-thyroxine absorption. To estimate the magnitude of tablet L-thyroxine malabsorption caused by calcium carbonate, with resulting increase in serum thyrotropin (TSH), we performed a cohort study in a referral care center.

METHODS

Fifty postmenopausal hypothyroid L-thyroxine-treated women (age 71.7 ± 5.1 years) who added calcium supplementation (600-1000 mg/day) were considered. They were taking L-thyroxine 45-60 min before breakfast (setting 1). After 4.4 ± 2.0 years from initiation of L-thyroxine therapy, they took calcium supplemaentation within 2 h after L-thyroxine taking (setting 2) for 2.3 ± 1.1 years. Hence, we recommended postponing calcium intake 6-8 h after L-thyroxine (setting 3). We evaluated TSH levels, the prevalence of women with elevated TSH (>4.12 mU/L), total cholesterolemia, fasting glycemia, blood pressure, and the prevalence of hypercholesterolemia, hyperglycemia, and hypertension.

RESULTS

TSH levels were 3.33 ± 1.93 mU/L versus 1.93 ± 0.51 or 2.16 ± 0.54 comparing setting 2 with setting 1 or 3 (P < 0.001, both). In setting 2, 18% women had elevated TSH versus none in setting 1 or 3 (P < 0.01). Total cholesterolemia, fasting glycemia, systolic, and diastolic blood pressure were also significantly higher in setting 2 compared to settings 1 and 3. For every 1.0 mU/L increase within the TSH range of 0.85-6.9 mU/L, total cholesterolemia, glycemia, systolic, and diastolic blood pressure increased by 12.1, 3.12 mg/dL, 2.31, and 2.0 mmHg, respectively.

CONCLUSIONS

Monitoring of hypothyroid patients who ingest medications that decrease L-thyroxine absorption should not be restricted to solely measuring serum TSH.

A minimum of two years of undertreated primary hypothyroidism, as a result of drug-induced malabsorption of l-thyroxine, may have metabolic and cardiovascular consequences

•

L-T4 malabsorption is frequently encountered in clinical practice.

•

Drug induced L-T4 malabsorption has metabolic and cardiovascular consequences.

•

Control of TSH is not enough when drug induced L-T4 malabsorption is suspected.

Objective

Cross-sectional studies have reported that TSH above or close to the upper normal limit correlates with unfavorable metabolic and cardiovascular outcomes. Certain medications impair intestinal absorption of levothyroxine (L-T4), resulting in undertreated hypothyroidism (viz. failure of serum TSH to reach target levels, if hypothyroidism is primary).

Further to evaluating the magnitude of sub-optimally treated primary hypothyroidism as a result of co-ingestion of those medications, we wished to ascertain whether the above complications would occur during a low number of years under polypharmacy.

Method

In this retrospective study in collaboration with 8 family physicians, we enrolled adults with primary hypothyroidism under L-T4 therapy that, for 2 years minimum, was not associated with those medications (non-exposure, baseline) and that, for another 2 years minimum, it was (exposure). Outcomes were serum levels and proportions of serum TSH levels >4.12 mU/L, and proportions of complications. Complications were aggravation of pre-existing or de novo onset of any of metabolic syndrome, impaired fasting glycemia (IFG), diabetes mellitus, dyslipidemia, hypertension, coronary heart disease (CHD), cerebrovascular disease (CVD).

Result

A total of 114 patients were enrolled. Duration of exposure to the interfering medication was 32.1 ± 6.9 months (median 31; range 24–55). Compared with non-exposure, the exposure period resulted in greater TSH levels (2.81 ± 3.62 [median 1.79] vs 1.27 ± 1.34 [median 0.93], P = 2.2 × 10⁻²⁰) and proportions of values >4.12 mU/L (18.5% vs 4.7%, P = 1.2 × 10⁻⁷). Seventy-six patients (67%) had complications, whose rates of TSH >4.12 mU/L were greater than in the 36 complication-free patients (22% vs 11%, P = 0.018).

Conclusion

During a median period of 31 months, there are relevant consequences for L-T4 treated adult hypothyroid patients resulting from hyperthyrotropinemia caused by medications impairing L-T4 absorption. This should be taken into account by future guidelines on hypothyroidism management.

Thyroid disorders in Brazil: the contribution of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Thyroid disorders are common diseases, both in Brazil and worldwide. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a prospective cohort study that investigates cardiovascular diseases, diabetes, and associated factors, including non-classical cardiovascular risk factors such as thyroid function. Thyroid function was classified according to thyrotropin stimulating hormone (TSH), free thyroxine (FT4), and use of medication to treat thyroid disorders, after excluding participants who reported use of any medication that could alter the results of the TSH and FT4 tests. All analyses included in this review are cross-sectional using baseline data (2008 to 2010). The results showed an association of subclinical thyroid disorders with biomarkers of subclinical atherosclerosis, measured by carotid intima-media thickness and coronary artery calcium, insulin resistance, metabolic syndrome, and some psychiatric disorders. No association was found with the biomarker of inflammation high-sensitivity C-reactive protein, or changes in pulse wave velocity or heart rate variability.

The Adverse Effects of Thyrotropin Absence on Pancreatic β Cell Function in Mice

Thyrotropin (TSH) is a modulator of glucose metabolism by binding to its receptor on pancreatic cells. We used thyrotropin receptor (TSHR) knockout mice (Tshr ^-/-) as a model of TSH deletion to study its function in pancreatic β cells. Tshr ^-/- mice had a similar body weight at birth compared with Tshr ^+/+ mice, but grew at a significantly slower rate until adulthood with adequate thyroxine supplementation. TSH deletion led to lower fasting and postprandial blood glucose, insulin secretion impairment, and atrophy of islets in adult mice. Transcription factors and markers of pancreatic β cell maturation, Pdx1, Nkx6.1, Glut2, and insulin, together with cell proliferation marker Ki67 showed no differences at the mRNA level between the two groups. However, the Bax/Bcl-2 ratio was remarkably elevated in Tshr ^-/- mice at both mRNA and protein levels. We hypothesized that pancreatic cell apoptosis, rather than abnormal cell proliferation and maturation, is associated with pancreatic dysfunction and glucose intolerance in the absence of TSH modulation.

The association between thyroid function and incidence of metabolic syndrome in euthyroid subjects: Tianjin chronic low-grade systemic inflammation and health cohort study

OBJECTIVE

Thyroid hormones (THs) are primarily responsible for the regulation of energy homeostasis and metabolism. However, few prospective studies have assessed the association between THs and metabolic syndrome (MetS) in a general population. We therefore designed a cohort study to examine whether serum TH levels within the reference range are predictive factors for developing MetS in adults.

DESIGN

Prospective cohort study.

PARTICIPANTS

A prospective study (n = 6119) was performed in Tianjin, China. Participants without a history of MetS were followed up for 1 to 3 years with a median follow-up duration of 2 years.

MEASUREMENTS

Serum free triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) levels were measured by chemiluminescence immunoassay. MetS was defined in accordance with the criteria of the American Heart Association scientific statements of 2009. THs, TSH levels and MetS were assessed yearly during the follow-up. Adjusted Cox proportional hazards regression models were used to assess the associations between FT3, FT4 and TSH quintiles and MetS.

RESULTS

The incidence of MetS was 17.7% (96 per 1000 person-years). In the final multivariate models, the hazard ratios (95% confidence interval) for MetS across serum FT3 quintiles were 1.00 (reference), 1.03 (0.84, 1.25), 1.14 (0.94, 1.38), 1.09 (0.90, 1.32) and 1.33 (1.11, 1.61), respectively (P for trend <.01). However, no significant associations between FT4, TSH and MetS were observed.

CONCLUSIONS

This population-based prospective cohort study suggests that increased serum FT3 level, rather than FT4 and TSH, is an independent predictor for developing MetS in euthyroid subjects.

[Hypertriglyceridemic waist phenotype: associated factors and comparison with other cardiovascular and metabolic risk indicators in the ELSA-Brasil study]

This study's objectives were to estimate the prevalence of hypertriglyceridemic waist (HTW) phenotype in participants in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), identify associated risk factors, and compare with other cardiovascular and metabolic risk indicators. This was a cross-sectional study with baseline data from a cohort of public employees. HTW is defined as the simultaneous presence of increased waist circumference (WC) (≥ 80cm for women, ≥ 90cm for men according to the International Diabetes Federation - IDF; and ≥ 88cm for women, ≥ 102cm for men according to the U.S. National Cholesterol Education Program - NCEP) and hypertriglyceridemia. Associations between independent variables and HTW were tested with multivariate logistic regression models. HTW was also compared to other cardiovascular and metabolic risk indicators by means of correlation tests, kappa index, sensitivity, and specificity. After exclusions, 12,811 participants were analyzed. Prevalence of HTW ranged from 24.7% (IDF) to 13.3% (NCEP). HTW was associated with age, excessive alcohol consumption, former smoking, low HDL, non-high HDL, and increased C-reactive protein, independently of gender or the criterion used to define HTW. HTW was associated with cardiovascular risk indicators, especially metabolic syndrome. The high prevalence of HTW and its association with cardiovascular risk indicators, especially metabolic syndrome, supports its use as a cardiometabolic risk screening tool in clinical practice.

High prevalence of insulin resistance among Brazilian chronic hepatitis C patients

OBJECTIVE

This study aims to estimate the prevalence of insulin resistance (IR) among chronic hepatitis C (CHC) patients and their related laboratory and demographic data.

SUBJECTS AND METHODS

In this study, non-diabetic CHC patients referred to Viral Hepatitis Ambulatories from Rio de Janeiro (Brazil) donated blood samples. Insulin was measured using a chemiluminescence immunoassay. IR was determined by HOMA-IR, where HOMA-IR > 2 was defined as IR.

RESULTS

A total of 214 CHC patients were recruited (123 females aged 53.6 years ± 10.9 years). IR was present in 133 patients (62.1%) and was associated in bivariate analysis to higher mean values of age (p = 0.040), triglycerides (p = 0.032), glucose (p = 0.000), insulin (p = 0.000), waist circumference (p = 0.001), and body mass index (p = 0.007); however, none of these variables were significant in the multivariate analysis.

CONCLUSIONS

The high prevalence of IR was observed among CHC patients, and there was no difference in clinical or laboratory parameters when both groups were compared in the multivariate analysis. This high IR prevalence could lead to a high risk for development of cardiovascular disease and metabolic disorders.

Lack of Association Between Subclinical Hypothyroidism and Carotid-Femoral Pulse Wave Velocity in a Cross-Sectional Analysis of the ELSA-Brasil

BACKGROUND

There is little available data on carotid-femoral pulse wave velocity (cf-PWV) in subjects with subclinical hypothyroidism (SCH). We aimed to analyze the association between SCH and cf-PWV using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS

We included subjects with normal thyroid function (thyrotropin (TSH): 0.4-4.0 mIU/l, and normal free thyroxine (FT4: 0.8-1.9ng/dl) and SCH (TSH > 4.0 mIU/l and normal FT4) evaluated for cf-PWV in a cross-sectional analysis. We excluded individuals using medications that interfere in thyroid function, antihypertensives, or diuretics, and subjects with chronic kidney disease or previous cardiovascular disease. Generalized linear and logistic regression models evaluated cf-PWV as a dependent variable and SCH as an independent variable, adjusted for cardiovascular risk factors.

RESULTS

Of 8,341 subjects (52.3% women), 7,878 (94.4%) were euthyroid and 463 (5.6%) showed SCH. The median age was 50 years (interquartile range: 44-56). The groups differed by age, sex, body mass index, glomerular filtration rate, and C-reactive protein. SCH was not associated with cf-PWV in the full-adjusted linear model (β = -0.039; P = 0.562) and with cf-PWV >75^th percentile in the full-adjusted logistic model (odds ratio = 0.94; 95% confidence interval = 0.72-1.22).

CONCLUSION

In a large sample, SCH was not associated with increased cf-PWV.

Thyroid Function and High-Sensitivity C-Reactive Protein in Cross-Sectional Results from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil): Effect of Adiposity and Insulin Resistance

BACKGROUND

Subclinical hypothyroidism (SCH) is associated with an increased cardiovascular risk, but little information is available about its association with high-sensitivity C-reactive protein (hs-CRP).

OBJECTIVES

This study aims to analyze the association between SCH and hs-CRP using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS

The study has a cross-sectional design. We included subjects with normal thyroid function (thyroid-stimulating hormone, TSH, 0.4-4.0 μIU/ml and normal free thyroxine, fT₄, 10.3-24.45 pmol/l) and SCH (TSH >4.0 μIU/ml and normal fT₄) who were evaluated for hs-CRP. We excluded individuals on medications that affect thyroid function and those who had prevalent cardiovascular disease. Multivariate linear regression evaluated hs-CRP and TSH as continuous variables, and logistic regression models assessed hs-CRP ≥19.05 nmol/l as the dependent variable and crescent quintiles of TSH as the independent variables adjusted for demographic and cardiovascular risk factors.

RESULTS

We included 12,284 subjects with a median age of 50 years (interquartile range = 45-57); 6,408 (52.2%) were female, 11,589 (94.3%) were euthyroid, and 695 (5.7%) had SCH. Bivariate analyses of participants stratified into quintiles of TSH revealed differences according to hs-CRP but not the Framingham risk score. The fifth quintile of TSH was not associated with elevated hs-CRP, odds ratio = 1.11 (95% confidence interval = 0.98-1.26), p = 0.102, in a fully adjusted logistic model, also consistent with the linear model (β = 0.024, p = 0.145).

CONCLUSIONS

TSH is not associated with hs-CRP. Obesity and insulin resistance are very important confounders in the study of the association between SCH and hs-CRP.

Subclinical hypothyroidism is associated with higher carotid intima-media thickness in cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

BACKGROUND AND AIM

Although subclinical hypothyroidism (SCH) is associated with cardiovascular risk, there is scarce data about subclinical atherosclerosis in subjects with SCH. We aimed to analyze the association between SCH and carotid intima-media thickness (IMT) using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS AND RESULTS

We included subjects with normal thyroid function (TSH: 0.4-4.0 mIU/l, and normal free thyroxine (FT4): 0.8-1.9 ng/dl) and SCH (TSH ≥ 4.0 mIU/l and normal FT4) evaluated for IMT in a cross-sectional analysis. We excluded individuals using medications that affect thyroid function and those with a history of cardiovascular disease. We performed logistic and linear regression models to evaluate the association with IMT (mean values and categorized at the 75th percentile) as a dependent variable and SCH as an independent variable, adjusted for other cardiovascular risk factors. From 8623 subjects (median age of 50 years; interquartile range: 44-57), 4624 (53.6%) were women, 8095 (93.9%) were euthyroid, and 528 (6.1%) had SCH. Groups varied in age, body mass index, Framingham risk score, Homeostasis Model Assessment for Insulin Resistance (HOMA-IR), C-reactive protein, as well as, IMT, that were all higher in SCH compared to euthyroid participants. SCH is associated with IMT as a continuous variable (β = 0.010, P = 0.036) and IMT >75th percentile: OR = 1.30 (95% CI = 1.06-1.59) in logistic models.

CONCLUSION

Individuals with SCH presented higher IMT compared with euthyroid subjects, even after adjustment for potential confounders. IMT was independently associated with SCH in the baseline of the ELSA-Brasil study.