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

Research status of subclinical hypothyroidism promoting the development and progression of cardiovascular diseases

In recent years, the incidence of cardiovascular disease (CVD) has risen steadily, significantly impacting public health. Subclinical hypothyroidism (SCH) remains a controversial risk factor for CVD. This review examines the associations between SCH and dyslipidemia, carotid intima-media thickness (C-IMT), cardiac dysfunction, and cardiovascular event risk. Evidence suggests SCH may exacerbate atherosclerosis and cardiac dysfunction through mechanisms such as increased LDL synthesis, oxidative stress, and impaired vascular endothelial function. However, the causal link between SCH and cardiovascular outcomes remains unclear due to study design heterogeneity and overreliance on TSH levels. Elevated TSH may not solely reflect thyroid dysfunction but could also indicate compensatory responses to inflammation, aging, or stress. Large-scale studies like NHANES and IPD meta-analyses show a strong association between SCH and cardiovascular risk in younger populations, which diminishes in older adults due to physiological TSH increases. The cardiovascular benefits of levothyroxine (L-T4) therapy in SCH patients are limited, especially in older individuals, where a narrow therapeutic window increases side effect risks. Studies relying solely on TSH as a diagnostic and therapeutic target have significant limitations, as TSH cannot distinguish adaptive thyroid adjustments from pathological states and overlooks the role of free thyroid hormones (FT3/FT4). Future research should integrate multi-dimensional markers (such as oxidative stress indicators, vascular elasticity measures, and thyroid antibody status) and adopt longitudinal study designs to more accurately assess the clinical significance of SCH.

Thyroid peroxidase antibodies were associated with prevalent carotid intima-media thickness in middle-age and older adults: the ELSA-Brasil cohort

PURPOSE

Understanding the relationship between antithyroperoxidase antibodies (TPOAb) and carotid intima-media thickness (cIMT) could provide insights into the mechanisms linking thyroid autoimmunity and cardiovascular disease. We aimed to explore the association of multiple categories of TPOAb with the increased cIMT at baseline and at follow-up in participants from the ELSA-Brasil Study.

METHODS

This prospective cohort study analyzed data from 9,264 participants (51.5 ± 8.9 years old, 55.9% women) without a history of cardiovascular disease. Fasting serum TPOAb levels were determined. Values of cIMT equal to or above one deviation standard of the sample's mean were classified as increased cIMT at baseline. The increased cIMT after the 8-year follow-up was calculated after excluding participants with increased cIMT at baseline. Multivariate analyses were done using binary logistic and Poisson regression models.

RESULTS

The increased cIMT was prevalent in 14.3% of the participants at baseline and its development occurred in 16.8% participants during the cohort. After adjustment for all confounder variables, TPOAb detectability (OR = 1.84, 95%CI = 1.21-2.79), and low detectable (OR = 1.81, 95%CI = 1.18-2.75), high detectable (OR = 2.01, 95%CI = 1.29-3.11) and positive (OR = 1.70, 95%CI = 1.07-2.70) TPOAb were positively associated with increased cIMT at baseline. The associations of low and high detectable TPOAb and increased cIMT at baseline were consistent when excluding those with thyroid dysfunction. There was no statistically significant association between TPOAb levels and increased cIMT at follow-up (p > 0.05), neither for all sample nor for euthyroid individuals.

CONCLUSION

Different levels of TPOAb, including its detectability, were associated with increased cIMT at baseline in the studied sample. We highlight that may be relevant to consider the levels of TPOAb detectability as possible marker of increased cardiovascular risk.

Deciphering thyroid function and CIMT: a Mendelian randomization study of the U-shaped influence mediated by apolipoproteins

Background

Carotid Intima-Media Thickness (CIMT) is a key marker for atherosclerosis, with its modulation being crucial for cardiovascular disease (CVD) risk assessment. While thyroid function's impact on cardiovascular health is recognized, the causal relationship and underlying mechanisms influencing CIMT remain to be elucidated.

Methods

In this study, Mendelian Randomization (MR) was employed to assess the causal relationship between thyroid function and CIMT. Thyroid hormone data were sourced from the Thyroidomics Consortium, while lipid traits and CIMT measurements were obtained from the UK Biobank. The primary analysis method was a two-sample MR using multiplicative random effects inverse variance weighting (IVW-MRE). Additionally, the study explored the influence of thyroid hormones on lipid profiles and assessed their potential mediating role in the thyroid function-CIMT relationship through multivariate MR analysis.

Results

The study revealed that lower levels of Free Thyroxine (FT4) within the normal range are significantly associated with increased CIMT. This association was not observed with free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), or TPOAb. Additionally, mediation analysis suggested that apolipoprotein A-I and B are involved in the relationship between thyroid function and CIMT. The findings indicate a potential U-shaped curve relationship between FT4 levels and CIMT, with thyroid hormone supplementation in hypothyroid patients showing benefits in reducing CIMT.

Conclusion

This research establishes a causal link between thyroid function and CIMT using MR methods, underscoring the importance of monitoring thyroid function for early cardiovascular risk assessment. The results advocate for the consideration of thyroid hormone supplementation in hypothyroid patients as a strategy to mitigate the risk of carotid atherosclerosis. These insights pave the way for more targeted approaches in managing patients with thyroid dysfunction to prevent cardiovascular complications.

Association Between Thyroid Parameters and Subclinical Atherosclerosis in Hospitalised Euthyroid Patients with Type 2 Diabetes Mellitus

Purpose

To explore the association between thyroid parameters and subclinical atherosclerosis (AS) in hospitalised euthyroid patients with type 2 diabetes mellitus (T2DM).

Patients and Methods

A retrospective analysis was conducted involving 1245 inpatients with T2DM. Free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) levels were measured, and carotid artery ultrasonography was performed. Thyroid hormone (TH) sensitivity was evaluated using thyroid feedback quantile-based index (TFQI), TSH index (TSHI), thyrotropin thyroxine resistance index (TT4RI), and free triiodothyronine/free thyroxine ratio (FT3/FT4).

Results

In inpatients with T2DM having normal thyroid function, the incidence of subclinical AS declined with increasing levels of FT3, FT4, and FT3/FT4 (P trend < 0.05). Logistic regression analysis revealed that FT4 (OR, 0.914; 95% CI, 0.845-0.989), FT3 (OR, 0.374; 95% CI, 0.277-0.504), and FT3/FT4 (OR, 0.036; 95% CI, 0.013-0.061) were independently associated with subclinical AS (P < 0.05). However, TSH, TFQI, TSHI, and TT4RI levels were not associated with subclinical AS (P > 0.05). FT3/FT4 demonstrated superior predictive accuracy for subclinical AS than that of FT3 or FT4 alone (P < 0.001), with a cutoff point of 0.25.

Conclusion

In euthyroid inpatients with T2DM, subclinical AS exhibited negative correlation with FT3, FT4, and FT3/FT4 levels, independent of other risk factors for AS. Additionally, FT3/FT4 ratio had a good predictive value for subclinical AS.

The association of diabetes, subclinical hypothyroidism and carotid intima-media thickness: results from the Brazilian Longitudinal Study of Adult Health (ELSA-Brazil)

INTRODUCTION

The association of diabetes with subclinical thyroid diseases may increase the risk of cardiovascular diseases. We analyzed the association of subclinical hypothyroidism, diabetes, and both diseases with carotid Intima-Media Thickness (cIMT) as a surrogate maker for early cardiovascular disease in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS

Cross-sectional analysis with data from the 3^rd visit (2017‒2019). Linear regression models were used to evaluate the association of subclinical hypothyroidism, diabetes and of both diseases with a cIMT presented as Beta (95% Confidence Interval ‒ 95% CI) without adjustment, with adjustment for sociodemographic variables (Model 1) and multivariable adjustment (Model 1 more cardiovascular risk factors). We also used logistic regression models to analyze the Odds Ratio (OR) and 95% CI for the association of both diseases using cIMT > P75%.

RESULTS

After the exclusion of patients with previous cardiovascular disease, 5,077 participants with no diseases, 1578 with diabetes, 662 with subclinical hypothyroidism, and 234 with both diseases were included in the analysis. Linear regression models showed an association of cIMT with only diabetes (β = 0.019; 95% CI 0.012 to 0.027; p < 0.0001) and subclinical hypothyroidism more diabetes (β = 0.03; 95% CI 0.010‒0.047, p < 0.0001). The logistic regression model reported an association between diabetes and CIMT higher than P75% (OR = 1.49, 95% CI 1.30‒1.71). No interaction between diabetes and subclinical hypothyroidism was detected using cIMT respectively as a continuous (p = 0.29) or as a categorical variable (p = 0.92).

DISCUSSION

Diabetes was associated with higher cIMT values. However, no additive effect of subclinical hypothyroidism associated with diabetes over cIMT was detected.

A Pilot Study of Subclinical Non-Capillary Peripapillary Perfusion Changes in Thyroid-Related Orbitopathy Detected Using Optical Coherence Tomography Angiography

Purpose

Hemodynamic changes surrounding the optic nerve head are known to occur in thyroid-related orbitopathy (TRO). This pilot study explores the capillary and non-capillary peripapillary perfusion changes of the retina in TRO eyes without dysthyroid optic neuropathy (DON) using optical coherence tomography angiography (OCT-A).

Methods

Non-capillary and capillary peripapillary perfusion densities were calculated using single 4.5 × 4.5mm en face “RPC layer” OCT-A scans of 8 TRO patients without DON (8 eyes, mean age 40.6 years, range 23–69 years). Results were compared to a previously published dataset of 133 healthy controls (133 eyes, mean 41.5 years, range 11–83 years). The strength of association was measured between OCT-A perfusion densities and clinical measures of TRO.

Results

Non-capillary peripapillary perfusion density in TRO eyes was found to be significantly decreased compared to healthy controls (TRO group 15.4 ± 2.9% vs controls 21.5 ± 3.1%; p < 0.0001). Capillary peripapillary perfusion densities showed no significant difference (TRO group 42.5 ± 1.8% vs controls 42.5 ± 1.5%; p = 1.0). Clinical measures of disease did not correlate well with OCT-A perfusion densities (p>0.05).

Conclusion

These findings may represent decreased blood flow and subclinical ischemia to the optic nerve. We discuss possible pathogenic mechanisms of thyroid-related vasculopathy, including vessel wall thickening due to immunologically-induced media enlargement.

Association of longitudinal trends in thyroid function with incident carotid atherosclerosis in middle-aged and older euthyroid subjects: the Tianjin Chronic Low-Grade Systemic Inflammation and Health (TCLSIH) cohort study

BACKGROUND

Previous studies have posited that an association exists between thyroid function and the heart and vasculature. It remains unclear, however, whether longitudinal trends in thyroid function contribute to the development of atherosclerosis. We conducted a cohort study to examine the association of longitudinal trends in thyroid function with incident carotid atherosclerosis (CA) in middle-aged and older euthyroid subjects.

METHODS

This cohort study's participants were recruited from the Tianjin Chronic Low-grade Systemic Inflammation and Health Cohort Study in Tianjin, China. Free triiodothyronine (FT3), thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured using chemiluminescence immunoassay. CA was assessed using carotid ultrasonography. Thyroid function and ultrasonography were assessed yearly during follow-up. Multivariable Cox proportional hazards regression models were used to assess the association between thyroid function and incident CA.

RESULTS

A total of 3,181 participants were enrolled in the cohort study. Within 7,762 person-years of follow-up, 944 participants developed CA, the incidence rate of CA was 122 per 1,000 person-years. The fully adjusted hazards ratios (95% confidence interval) of CA for per 1-unit increase in changes of FT3, FT4 and TSH were 1.34(1.22-1.47), 1.22(1.19-1.26) and 0.92 (0.77-1.09) (P < 0.0001, <0.0001 and = 0.32, respectively), respectively. Similar significant associations between mean levels of FT3 and FT4 and incident CA were observed. However, baseline thyroid function was not associated with incident CA.

CONCLUSIONS

These findings suggest that higher mean levels and higher values of changes in thyroid hormones were associated with a higher risk of incident CA in middle-aged and older euthyroid subjects.

Urinary iodine and sodium concentration and thyroid status in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

OBJECTIVES

To evaluate urinary iodine concentration (UIC) in civil servants aged 35-74 years of the Brazilian Study of Adults Health (ELSA-Brasil) to analyze its relationship with sociodemographic, clinical risk factors, lifestyle, urinary Na and thyroid status.

DESIGN

Cross-sectional study in six Brazilian cities.

METHODS

This analysis included 792 participants with information about urinary iodine concentration (UIC). Thyroid status was defined by serum levels of TSH/FT4 and the current use of antithyroid drugs for treatment of overt hyperthyroidism or levothyroxine to treat overt hypothyroidism. The determination of UIC was carried out with an inductively coupled plasma mass spectrometer (ICP-MS) and was expressed as median with Interquartile Range (IQR).

RESULTS

In 792 participants, thereof 52% women, mean age was 51.9 (9.0) years. The median UIC was 219 (IQR, 166-291) for all persons studied, thereof 211 (IQR, 157-276) for women and 231 (IQR, 178-304) for men. According to the WHO classification, for all persons studied, 60% had more than adequate iodine-supply (UIC ≥200 μg/L), 37% were adequately supplied (UIC 100-199 μg/L) and <3% had a deficient iodine status (<100 μg/L). In the 35-44-year age strata, which includes women of childbearing age, 23.2% of women presented less than 150 μg/L of UIC. No differences in UIC were detected according to thyroid status. (P = 0.39) The correlation between Ur-Na and UIC showed a Spearman coefficient of 0.52 (P < 0.0001) and it was also found an association of Ur-Na with UIC: Beta of 1.76 (95% Confidence Interval (95% CI): 1.01 to 2.51. The urinary Na concentration showed a synergy with the UIC, that means medians of 57, 72, 107 and 141 mmol Na/L urine (P < 0.001) in the groups with the four UIC classes according to the WHO grading mentioned above. The very low Na content in the persons exhibiting <100 μg/L UIC seems to reflect also a higher urine volume due to the frequent use of diuretics. The strong relationship between the urinary Na concentration and the UIC points to a dependence of the UIC on the individual consumption of iodized salt, which should be more considered in future studies. The strong relationship between the urinary Na concentration and the UIC points to a dependence of the UIC on the individual consumption of iodized salt, which should be more considered in future studies.

CONCLUSIONS

Euthyroid persons were dominating by more than four fifths and no significant association was found between UIC and thyroid status. Although most of the persons studied present more than adequate iodine intake it was observed that nearly a quarter of women in childbearing age are iodine deficient.

Subclinical Hypothyroidism in Patients with Diabetic Retinopathy: Role of Vascular Endothelial Growth Factor

BACKGROUND

Considering the vital role of vascular endothelial growth factor (VEGF) in the development of diabetic retinopathy (DR) in one hand and the frequent association between subclinical hypothyroidism (SCH) and DR on the other hand.

OBJECTIVE

The present study was proposed to explore the possible role of VEGF in the relation between SCH and DR, thus we investigated the relation between SCH and VEGF levels in patients with DR.

METHODS

Two hundred patients with DR were recruited in this study [100 patients with proliferative diabetic retinopathy (PDR) and 100 patients with non-proliferative diabetic retinopathy (NPDR)]. Patients with DR were divided into 2 groups according to thyroid function: patients with SCH or those with euthyroidism. Patients were subjected to careful history taking, and underwent clinical and ophthalmological examination. Fasting blood glucose, glycosylated hemoglobin, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), TSH, FT4, FT3, VEGF and thyroid volume were assessed Results: Among all the studied patients, 21.5% (43/200) had SCH. DR patients with SCH had higher age, diabetes duration, HbA1c, HOMA-IR and VEGF than those with euthyroidism. The frequency of PDR in patients with SCH was 72.1% (31/43) and 43.9% (69/157) in those with euthyroidism, whereas the frequency of NPDR in patients with SCH was 27.9 (12/43) and 56.1% (88/157) in those with euthyroidism (P < 0.003). In multivariate analysis, PDR, HOMA-IR and VEGF levels were the significant predictor variables of SCH.

CONCLUSIONS

Increased VEGF levels may be implicated in the relationship between SCH and DR.

The role of thyroid hormones in carotid arterial wall remodeling in women

INTRODUCTION

Thyroid hormones affect the cardiovascular system, but the precise mechanisms of their effects on the development of atherosclerosis are not entirely clear. The relationship between subclinical hypothyroidism, dyslipidemia and carotid atherosclerosis has been widely investigated, but the findings were controversial. The aim of the present study was to determine whether female subjects with subclinical hypothyroidism (SHypo) have increased carotid intima-media thickness (IMT) compared with euthyroid subjects, as well as to examine the association of SHypo, carotid atherosclerosis and dyslipidemia.

METHODS

This research included 100 women aged 30 to 70 years who were divided into two groups: the SHypo group including subjects with signs of subclinical hypothyroidism and the control group of euthyroid subjects. Carotid IMT thickness using B mode ultrasound was determined and its correlation with serum concentrations of fT4, TSH, CRP, and lipid profile including small dense LDL (sdLDL) was analysed.

RESULTS

Subjects with SHypo had significantly increased carotid IMT (IMT ≥ 75th centile) in all three measured segments of the right (p <0.001) and the left (p = 0.001) carotid artery compared to the control group, with a significantly more frequent appearance of plaque (25% vs. 9%; p = 0.05). Significant positive correlations were found between higher TSH and higher IMT values. Increased age, LDL cholesterol, and TSH predicted thickening of the carotid artery IMT.

CONCLUSIONS

It is important to screen people showing early, subclinical signs of thyroid gland dysfunction due to its impact on carotid atherosclerosis development.

Lymphocyte to monocyte ratio may predict increased carotid intima-media thickness in patients with subclinical hypothyroidism

BACKGROUND

Inflammation has an important role in the pathogenesis of atherosclerosis. Lymphocyte-to-monocyte ratio (LMR) is accepted as an indicator of inflammation.

OBJECTIVE

Our aim was to scrutinize the relationship between LMR and subclinical atherosclerosis (SubAth) measured by carotid intima-media thickness (CIMT) in subclinical hypothyroidism (SubHT).

METHODS

Newly identified 190 SubHT patients were prospectively included into the study. Blood samples were taken for measuring laboratory parameters. Then, CIMT was computed. Patients were seperated into 2 groups by their CIMT value (Group-1: ≤0.9 and Group-2: >0.9 mm), and then stratified into tertiles pursuant to LMR and thyroid-stimulating hormone (TSH) levels, respectively.

RESULTS

59 patients had an increased CIMT value (Group-2), and 131 patients had a normal CIMT value (Group-1). Group-2 had a lower LMR and a greater high-sensitivity C-reactive protein (hsCRP), CIMT and TSH than Group-1 (for all, p < 0.05). Patients in the lowest tertile of LMR had a higher hsCRP, TSH and CIMT than those in the highest tertile (for all, p < 0.05). LMR was negatively associated with hsCRP, CIMT and TSH (for all, p < 0.05). LMR and TSH were independent predictors of increased CIMT.

CONCLUSIONS

Pre-ultrasonographic LMR, which is a simple and inexpensive inflammatory marker, may give additional predictive information to determine SubAth in SubHT.

Unfavorable Triglyceride-rich Particle Profile in Subclinical Thyroid Disease: A Cross-sectional Analysis of ELSA-Brasil

Subclinical thyroid disorders have been associated with atherosclerosis and increased cardiovascular risk. As triglyceride-rich lipoprotein particles (TRLPs) have recently emerged as a casual factor for atherogenesis, the aim of this study was to evaluate the relationship between subclinical hypo- and hyperthyroidism and TRLP subfractions. We selected 5066 participants from the ELSA-Brasil cohort with available data of thyroid function and lipid profile measured by nuclear magnetic resonance (NMR) spectroscopy. Individuals were divided into 3 groups by baseline thyroid function (subclinical hypothyroidism, euthyroidism, and subclinical hyperthyroidism). Triglyceride-rich lipoprotein particle subfractions were analyzed through NMR spectroscopy. To examine the association between TRLP subfractions and thyroid function, we conducted univariate and multivariate linear regression models adjusted for demographic characteristics, body mass index, diabetes, smoking status, and alcohol use. Of 3304 individuals, 54% were women, with a mean age of 50.6 ± 8.7 years, 51% white, and 53% with at least a college education. Of these individuals, 92% were euthyroid, whereas 6.8% had subclinical hypothyroidism and 1.2% had subclinical hyperthyroidism. The univariate linear regression showed that very small TRLPs (P = 0.026) and very large TRLPs (P = 0.008) were statistically increased in subclinical hypothyroidism when compared with euthyroidism. In subclinical hyperthyroidism, there was a reduction in total TRLPs (P = 0.003), seemingly driven by reduced very small TRLPs (P = 0.067). The findings were confirmed when adjusted for demographic characteristics, as well as comorbidities. This study suggests that subclinical hypothyroidism is associated with very small and very large TRLPs, which are related to an unfavorable atherogenic profile. Subclinical hyperthyroidism is associated to lower very small TRLPs.

Hypothyroidism and risks of cerebrovascular complications among patients with head and neck cancer after radiotherapy

BACKGROUND

Hypothyroidism (HT) and carotid artery stenosis (CAS) are complications of radiotherapy (RT) in patients with head and neck cancer (HNC). The impact of post-RT HT on CAS progression remains unclear.

METHODS

Between 2013 and 2014, HNC patients who had ever received RT and were under regular follow-up in our hospital were initially screened. Patients were categorized into euthyroid (EU) and HT groups. Details of RT and HNC were recorded. Total plaque scores and degrees of CAS were measured during annual extracranial duplex follow-up. Patients were monitored for CAS progression to > 50 % stenosis or ischemic stroke (IS). Cumulative time to CAS progression and IS between the 2 groups were compared. Data were further analyzed based on the use or nonuse of thyroxine of the HT group.

RESULTS

333 HNC patients with RT history were screened. Finally, 216 patients were recruited (94 and 122 patients in the EU and HT groups). Patients of the HT group received higher mean RT doses (HT vs. EU; 7021.55 ± 401.67 vs. 6869.69 ± 425.32 centi-grays, p = 0.02). Multivariate Cox models showed comparable CAS progression (p = 0.24) and IS occurrence (p = 0.51) between the 2 groups. Moreover, no significant difference was observed in time to CAS progression (p = 0.49) or IS (p = 0.31) among patients with EU and HT using and not using thyroxine supplement.

CONCLUSIONS

Our results did not demonstrate significant effects of HT and thyroxine supplementation on CAS progression and IS incidence in patients with HNC after RT.

Thyroid Dysfunction and Atherosclerosis: A Systematic Review

BACKGROUND/AIM

Thyroid dysfunction, both hypo- and hyperthyroidism, has been associated with cardiovascular disease. The aim of this study was to evaluate the association between thyroid dysfunction and atherosclerosis measured mostly by carotid intima-media thickness, as well as discuss whether L-T4 replacement is able to reverse or slow down the progression of atherosclerosis.

MATERIALS AND METHODS

The review was conducted according the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. We performed on PubMed a literature search from May 2004 to January 2020, using the search terms 'subclinical hypothyroidism' or 'thyroid disorders' and 'carotid artery', 'carotid intima-media thickness (IMT)', 'levothyroxine', and 'atherosclerosis'.

RESULTS

Twenty-six studies were eligible and included in the analysis. Overall, the studies encompassed a total of 36.434 patients included in this review. Most studies indicated a proportional correlation between IMT and thyroid dysfunction. Levothyroxine (L-T4) replacement led to significant decrease of IMT after 1 year in most studies.

CONCLUSION

Most studies have concluded that thyroid dysfunction is associated with arterial wall remodeling and, thus, with increased cardiovascular risk. However, the exact mechanistic background of pathological structural changes in the arterial wall is still unsettled. Large randomized controlled studies are required to definitively address the extent to which T4 replacement therapy might benefit patients with subclinical thyroid disorders.

Differences in HDL particle size in the presence of subclinical thyroid dysfunctions: The ELSA-Brasil study

BACKGROUND AND AIMS

Thyroid dysfunction is related to several lipid abnormalities. There is no consensus about concentration of high-density lipoprotein (HDL) in different studies. The aim of this report is to evaluate HDL particle (HDL-P) subfractions across a spectrum of thyroid functions in a Brazilian population.

METHODS

Individuals were divided into three groups by baseline thyroid function (subclinical hypothyroidism, euthyroidism, and subclinical hyperthyroidism). HDL-P subfractions were analyzed by Nuclear Magnetic Resonance (NMR) spectroscopy. To examine the association between HDL-P subfractions and thyroid function, we used univariate and multivariate linear regression models adjusted for demographic characteristics, comorbidities, lifestyle factors, and traditional lipid measurement (HDL-C, LDL-C and triglycerides).

RESULTS

Of 3304 participants, 54.1% were women, 51.2% white, with mean age 50.6 ± 8.7 years. HDL-C and triglycerides levels (p = 0.032 and p = 0.016, respectively) were higher in the SC hypothyroid group. There were no statistically significant differences in total cholesterol levels and LDL-C levels. In univariate analysis, small HDL-P subfractions were significantly lower in subclinical hypothyroidism (p = 0.026) whereas intermediate HDL-P were higher in subclinical hyperthyroidism (p = 0.049), compared to euthyroidism. After adjustment for demographic data, SC hypothyroidism was still statistically associated with lower levels of small HDL-P. After adjusting for comorbidities, lifestyle factors, and traditional lipid measurements, SC hypothyroidism had an established association with lower levels of small HDL-P while SC hyperthyroidism was associated with lower levels of large HDL-P.

CONCLUSIONS

In this large cohort from a Brazilian population, subclinical hypothyroidism was associated with lower small HDL-P subfractions, and subclinical hyperthyroidism with lower large HDL-P subfractions and higher intermediate HDL-P subfractions.

Subclinical Hypothyroidism and Lipid Metabolism: To Treat or Not to Treat?

Thyroid hormones have multiple complex effects on lipid synthesis and metabolism. These physiological actions are well documented in overt hypothyroidism where the elevated levels of total cholesterol, low density lipoporotein cholesterol and possibly triglycerides are reverted by levo-thyroxine therapy. Subclinical hypothyroidism, defined as elevated serum thyroid stimulating hormone in the presence of reference range of free thyroxine and free triiodothyronine concentrations, is a relatively frequent clinical conditions. Many clinical and epidemiological studies have evaluated lipid metabolism, markers of subclinical atherosclerosis and other cardiovascular risk factors in subclinical hypothyroidism as well as the need of replacement therapy in these patients. The available results are rather conflicting, with variable and inconclusive results. Moreover, no consensus still exists on the clinical significance and treatment of this mild form of thyroid failure. On the contrary, available evidences suggest that patients with plasma thyroid stimulating hormone levels above 10 mU/L should be treated with levo-thyroxine, since may have an increased risk of cardiovascular disease. However, the epidemiological evidences suggest being rather conservative in older people, since higher thyroid stimulating hormone is associated with lower risk of multiple adverse events in this population. In this review, we summarized the current evidences on the association between subclinical hypothyroidism and lipid metabolism and the effect of levo-thyroxine therapy on lipid parameters.

Subclinical hypothyroidism and cardiovascular risk factors

INTRODUCTION

Thyroid hormones have multiple effects on lipid metabolism as well as on the cardiovascular system function. These negative cardiovascular effects have long been recognized in overt hypothyroidism but can be reversed by treatment with levothyroxine.

EVIDENCES ACQUISITION

We performed on PubMed a literature search for the articles published until March 2019 by using the search terms "subclinical hypothyroidism," "cardiovascular disease," "cholesterol," "LDL," "HDL," "triglycerides," "coronary heart disease," "heart failure," "atherosclerosis," "all-cause mortality," "levothyroxine."

EVIDENCES SYNTHESIS

Subclinical hypothyroidism, defined as an elevated thyrotropin (TSH) with a normal free thyroxine (FT4), is frequent in the general population and increase with age. Subclinical hypothyroidism has been linked to cardiovascular risk factors, dyslipidemia and increased atherosclerosis. Although some studies have demonstrated that lipids are elevated in subclinical hypothyroidism, other studies did not confirm these data. Clinical trials have also demonstrated there is no clear evidence that levothyroxine therapy in subjects with milder form (TSH<10 mU/L) of subclinical hypothyroidism could improve lipid status and the other cardiovascular risk factors. Nevertheless, TSH level seems the best predictor of cardiovascular disease, in particular when its levels are above 10 mU/L.

CONCLUSIONS

Prospective studies are necessary to clarify the cardiovascular risk in patients with mild subclinical hypothyroidism and to assess the importance of treating elderly people in order to improve or counteract the correlated risks. However, until clinical recommendations will be updated, the decision to treat or not treat patients with subclinical hypothyroidism will still base on clinical judgment, clinical practice guidelines, and expert opinion.

Serum TSH level in obese children and its correlations with atherogenic lipid indicators and carotid intima media thickness

Objective: Moderately elevated level of thyroid-stimulating hormone accompanied by normal serum concentrations of free thyroxine, suggesting subclinical hypothyroidism, is the most common hormonal abnormality in obese children. Controversy remains, whether a thyroid dysfunction related to obesity has an influence on the cardiovascular risk factors. The aim of the study was to assess correlation between thyroid-stimulating hormone and free thyroxine and chosen atherogenic lipid indicators, and carotid intima media thickness in obese children and adolescents. Methods: A study group consisted of 110 obese children (11.5 ± 2.9 years) and 38 healthy children (13.4 ± 2.6 years). Obesity was defined using International Obesity Task Force criteria. In each patient anthropometric measurements, thyroid-stimulating hormone, free thyroxine, a lipid profile were evaluated. Carotid intima-media thickness was measured in 74 obese children and 28 lean children. The resulting data were used to calculate indicators of atherogenesis: total cholesterol to HDL cholesterol ratio; triglycerides to HDL cholesterol ratio and LDL cholesterol to HDL cholesterol ratio. Results: Obese children had higher mean serum thyroid-stimulating hormone levels compared to their lean peers and an adverse atherogenic lipid profile. Serum free thyroxine concentrations were comparable between the groups. Serum thyroid-stimulating hormone values correlated with total cholesterol to HDL cholesterol ratio; triglycerides to HDL cholesterol ratio, LDL cholesterol to HDL cholesterol ratio, and intima-media thickness. In a multivariate regression analysis, thyroid-stimulating hormone weakly correlated only with intima-media thickness after adjustment for age, gender and Body Mass Index (β = 0.249, p = 0.04). This relationship weakened after considering a lipid profile (β = 0.242, p = 0.058). No relationship was found for free thyroxine. Conclusion: Serum level of thyroid-stimulating hormone in obese children did not seem to impact atherogenic lipid indicators and carotid intima-media thickness. Therefore, an adverse lipid profile should still be considered the main risk factor for development of cardiovascular diseases in obese children.

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.

Relationship of thyroid function with intracranial arterial stenosis and carotid atheromatous plaques in ischemic stroke patients with euthyroidism

This study aimed to help clarify the possible relationships of thyroid function with intracranial arterial stenosis or carotid atheromatous plaques in ischemic stroke patients with euthyroidism. We retrospectively reviewed the medical records of a consecutive series of ischemic stroke patients prospectively entered into the Chengdu Stroke Registry between February 2010 and March2012. We performed univariate and multivariate analysis to assess possible relationships of thyroid function with intracranial artery stenosis or carotid atheromatous plaques. Of the 172 patients analyzed (42 women; 61.7 ± 14.0 years old), 62 (32.0%) had carotid atheromatous plaques, and 81 (47.1%) had intracranial artery stenosis. Free thyroxine levels were lower in patients with carotid atheromatous plaques than in patients without plaques (15.80±2.09 vs. 16.92±2.69, P = 0.005). After adjusting for age, gender, hyperlipidemia, and previous smoking, free thyroxine levels were independently associated with carotid atheromatous plaques (OR 0.73, 95% CI 0.54-0.99, P = 0.04). In contrast, thyroid function indicators showed no associations with intracranial arterial stenosis. In conclusion, low free thyroxine levels were independently associated with carotid atheromatous plaques in ischemic stroke patients with euthyroidism, but thyroid function indicators were not associated with intracranial artery stenosis.

Thyrotropin and free thyroxine levels and coronary artery disease: cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Data on the association between subclinical thyroid dysfunction and coronary artery disease (CAD) is scarce. We aimed to analyze the association between thyroid function and CAD using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). We included subjects with normal thyroid function (0.4-4.0 mIU/L, and normal free thyroxine, FT4, or 0.8 to 1.9 ng/dL), subclinical hypothyroidism (SCHypo; TSH>4.0 mIU/L and normal FT4), and subclinical hyperthyroidism (SCHyper; TSH<0.4 mIU/L and normal FT4) evaluated by coronary computed tomography angiography. We excluded individuals using medications that interfere in thyroid function or with past medical history of cardiovascular disease. Logistic regression models evaluated the presence of CAD, segment involvement score (SIS) >4, and segment severity score (SSS) >4 of coronary arteries as the dependent variables, and quintiles of TSH and FT4 as the independent variables, adjusted for demographical data and cardiovascular risk factors. We included 767 subjects, median age 58 years (IQR=55-63), 378 (49.3%) women, 697 euthyroid (90.9%), 57 (7.4%) with SCHypo, and 13 (1.7%) with SCHyper. No association between TSH and FT4 quintiles and CAD prevalence was noted. Similarly, no association between TSH levels and the extent or severity of CAD, represented by SIS>4 and SSS>4 were seen. Restricting analysis to euthyroid subjects did not alter the results. TSH levels were not significantly associated with the presence, extent, or severity of CAD in a middle-aged healthy population.

Treated hypothyroidism is associated with cerebrovascular disease but not Alzheimer's disease pathology in older adults

Thyroid hormone disease is common among older adults and is associated with cognitive impairment. However, pathologic correlates are not well understood. We studied pathologic and clinical factors associated with hypothyroidism, the most common manifestation of thyroid disease, in research subjects seen annually for clinical evaluations at U.S. Alzheimer's Disease Centers. Thyroid disease and treatment status were assessed during clinician interviews. Among autopsied subjects, there were 555 participants with treated hypothyroidism and 2146 without known thyroid disease; hypothyroidism was associated with severe atherosclerosis (odds ratio: 1.35; 95% confidence interval: 1.02, 1.79) but not Alzheimer's disease pathologies (amyloid plaques or neurofibrillary tangles). Among participants who did not undergo autopsy (4598 with treated hypothyroidism and 20,945 without known thyroid hormone disease), hypercholesterolemia and cerebrovascular disease (stroke and/or transient ischemic attack) were associated with hypothyroidism, complementing findings in the smaller autopsy sample. This is the first large-scale evaluation of neuropathologic concomitants of hypothyroidism in aged individuals. Clinical hypothyroidism was prevalent (>20% of individuals studied) and was associated with cerebrovascular disease but not Alzheimer's disease-type neuropathology.

Carotid intima-media thickness in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil): a narrative review

BACKGROUND

Carotid intima-media thickness (CIMT), as measured by ultrasound, has been used in large studies as a non-invasive marker for subclinical atherosclerosis. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a cohort of 15,105 civil servants in six Brazilian cities that included CIMT evaluation in its baseline assessment. The aim of the present narrative review was to provide an overview of ELSA-Brasil CIMT articles published up to July 31, 2017.

DESIGN AND SETTING

Narrative review of ELSA-Brasil CIMT studies using baseline assessment data.

METHODS

We searched PubMed for the terms "ELSA-Brasil" and "intima-media". This search yielded 21 published articles using CIMT data from the ELSA-Brasil baseline assessment, which were included in this review. We also present information about intima-media thickness assessment from ongoing onsite reevaluations of the study participants.

RESULTS

Most published studies focused on the association with traditional and novel cardiovascular risk factors. Studies also presented information about the ELSA-Brasil CIMT protocol at baseline and CIMT value distribution in this large sample.

CONCLUSIONS

Analyses on the ELSA-Brasil data led to important insights on CIMT interpretation and physiology. Besides the highlighted contributions which have already been made in this field, new data gathered during the ongoing third onsite assessment will enable investigation of substantially new research questions.

Thyrotrophin levels and coronary artery calcification: Cross-sectional results of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

OBJECTIVE

There is little information about the association between thyrotrophin (TSH) levels and coronary artery calcification (CAC). Our aim was to analyse the association between TSH quintiles and subclinical atherosclerosis measured by CAC, using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

DESIGN

Cross-sectional study.

PATIENTS

We excluded individuals using medications that affect thyroid function and who self-reported cardiovascular disease. We included euthyroid subjects and individuals with subclinical hypothyroidism (SCHypo) and subclinical hyperthyroidism (SCHyper). Logistic regression models evaluated CAC >100 Agatston units as the dependent variable, and increasing quintiles of TSH as the independent variable, adjusted for demographic and cardiovascular risk factors.

RESULTS

Our sample included 3836 subjects, mean age 49 years (interquartile range 44-56); 1999 (52.1%) were female, 3551 (92.6%) were euthyroid, 239 (6.2%) had SCHypo and 46 (1.2%) had SCHyper. The frequency of women, White people and never smokers as well as body mass index and insulin resistance increased according to quintiles. The 1st quintile for TSH (0-0.99 mIU/L) was associated with CAC >100, using the 3rd quintile (1.39-1.85 mIU/L) as reference (adjusted OR=1.57, 95% CI: 1.05-2.35, P=.027), but no association was shown for the 5th quintile (2.68-35.5 mIU/L) compared to the 3rd. Restricting the analysis to euthyroid subjects did not change the results. For women, but not for men, we observed a U-shaped curve with 1st and 5th TSH quintiles associated with CAC>100.

CONCLUSION

Low and low-normal (1st quintile) TSH levels were associated with CAC>100 Agatston units in a sample with subclinical thyroid disorders and euthyroid subjects.

Correlation between Thyroid Stimulating Hormone and Renal Function in Euthyroid Residents of Japan: Results from the Kyushu and Okinawa Population Study (KOPS)

Aim: The present large-scale Japanese population study was performed to evaluate the relation between the serum thyroid stimulating hormone (TSH) level and renal function.

Methods: Out of 1,374 residents who participated in a free public physical examination between 2010 and 2011, we evaluated the data of 888 participants for whom the serum TSH level and estimated glomerular filtration rate (eGFR) were successfully measured. The participants were categorized into three groups based on TSH levels (normal TSH, ≤ 2.4; high-normal TSH, 2.5–4.4; and subclinical hypothyroid, ≥ 4.5 µIU/mL). Multiple linear regression analysis adjusted for cardiovascular risk factors was performed to determine the relationship between serum TSH level and renal function.

Results: The mean ± SD TSH level was 2.0 ± 1.4 µIU/mL, and 75.9% (n = 674) of the participants had normal, 17.9% (n = 159) had high-normal, and 6.2% (n = 55) had subclinical hypothyroid TSH levels. The mean eGFR significantly decreased with increased TSH levels (normal TSH, 79.3 ± 14.1; high-normal TSH, 77.4 ± 13.0; and subclinical hypothyroid, 72.3 ± 12.2 mL/min/1.73 m²: P for trend < 0.01). Multiple linear regression analysis extracted log-transformed TSH level as an independent factor correlated with eGFR in the high-normal TSH group (beta = −0.18, P = 0.02).

Conclusions: Our findings demonstrated a significant correlation between serum TSH levels and eGFR in high-normal TSH participants. In healthy individuals, high-normal TSH levels indicate increased the risk of chronic kidney disease.