Sex-specific associations between thyrotropin and serum lipid profiles

TSH is independently associated with remnant cholesterol in euthyroid adults: a cross-sectional study based on 29,708 individuals

PURPOSE

The study aims to investigate the relationship between thyroid-stimulating hormone (TSH) and remnant cholesterol (RC) in euthyroid adults.

METHODS

The adults who were recruited for the study had undergone physical examination at Beijing Chao-Yang Hospital. High RC levels were defined as the upper quartile of RC levels in males and females, respectively. The relationship between TSH and RC was assessed using the logistic and linear regression models.

RESULTS

A total of 29,708 adults (14,347 males and 15,361 females) were enrolled in this study. RC ≥ 0.77 mmol/L in males and RC ≥ 0.60 mmol/L in females were defined as high RC levels. With increasing serum TSH levels, the percentage of adults with high RC levels increased. The odds ratios (ORs (95% confidence intervals (CIs)) for high RC levels increased as TSH quartiles (Q) rose after full adjustments [males: Q2 1.11 (1.00-1.24), P < 0.05; Q3 1.03 (0.92-1.15), P > 0.05; Q4 1.25 (1.12-1.40), P < 0.001; and females: Q2 1.07 (0.96-1.20), P > 0.05; Q3 1.17 (1.05-1.31), P < 0.01, Q4 1.33 (1.20-1.48), P < 0.001, all P for trend < 0.001], using Q1 as the reference.

CONCLUSION

Higher TSH levels were independently associated with higher RC levels in euthyroid adults, this underscoring the significance of regulating TSH levels appropriately.

The Impact of Thyroid Hormones on Cardiometabolic Risk in Children and Adolescents with Obesity, Overweight and Normal Body Mass Index (BMI): A One-Year Intervention Study

Thyroid hormones regulate metabolism and have a major impact in maintaining cardiovascular homeostasis. The purpose of our study was to examine the relation of thyrotropin (TSH) and thyroid hormones with cardiometabolic parameters in children and adolescents with obesity, overweight, and normal body mass index (BMI) before and after the implementation of a comprehensive, multidisciplinary, personalized, lifestyle intervention program for 1 year. One thousand three hundred and eleven (n = 1311) children and adolescents aged 2 to 18 years (mean age ± SD: 10.10 ± 2.92 years) were studied prospectively. Patients were categorized as having obesity (n = 727, 55.45%), overweight (n = 384, 29.29%) or normal BMI (n = 200, 15.26%) according to the International Obesity Task Force (IOTF) cutoff points. All patients received personalized guidance on diet, sleep, and physical activity at regular intervals throughout the 1-year period. Detailed clinical evaluation and hematologic, biochemical and endocrinologic investigations were performed at the beginning and the end of the study. Subjects with obesity had a more adverse cardiometabolic risk profile than subjects with overweight and normal BMI on both assessments. At initial evaluation, total T3 concentrations were positively associated with uric acid and HbA1C, and free T4 concentrations were negatively associated with insulin concentrations, while there was no association between TSH concentrations and cardiometabolic risk parameters. Following the 1 year of the multidisciplinary, lifestyle intervention program, the concentrations of lipids, HbA1C, ALT, and γGT improved significantly in all subjects. Changes in TSH concentrations were positively associated with changes in systolic blood pressure (SBP), glucose, triglycerides, and cholesterol concentrations. Changes in free T4 concentrations were negatively associated with changes in cholesterol and insulin concentrations. Furthermore, changes in T3 concentrations were positively associated with changes in HbA1C, glucose, uric acid, and triglyceride concentrations. These findings indicate that in children and adolescents with overweight and obesity, thyroid hormones are associated with indices conferring cardiometabolic risk.

Age-specific serum thyrotropin reference range for the diagnosis of subclinical hypothyroidism and its association with lipid profiles in the elderly population

The overdiagnosis of subclinical hypothyroidism (SCH) in the elderly has driven researchers to establish age-specific thyroid stimulating hormone (TSH) intervals to precisely evaluate the prevalence of SCH. Moreover, abnormal lipid profiles, an insidious manifestation of SCH, show various impacts on different age groups. This study aimed to establish an age-specific TSH reference range to clarify the spectrum of SCH in the elderly. The prevalence of dyslipidemia and the age-specific association between TSH and lipid profiles were analyzed to elucidate the relationship between SCH and dyslipidemia. This cross-sectional study enrolled 2460 participants aged ≥ 65 years via cluster sampling. All participants received physical, laboratory tests and thyroid ultrasound examination and completed the questionnaire. The chi-square test was used to analyze variations of dyslipidemia prevalence among different groups. The Cochran-Armitage trend test was applied for testing the linear trends of age-specific prevalence of dyslipidemia among different TSH intervals in each age group. After adjusting for confounding factors, the age-specific association between TSH and lipid profiles was identified using multi-variate linear regression analysis. The TSH reference ranges in the 65-70 age group, 71-80 age group and > 80 age group were 0.65-5.51 mIU/L, 0.85-5.89 mIU/L and 0.78-6.70 mIU/L, respectively. Using these age-specific reference ranges, the prevalence of SCH in the whole population was 3.74%, which was significantly lower than the prevalence based on the laboratory reference range (10.28%). In the 65-70 age group, only the prevalence of high total cholesterol (TC) increased significantly with the age-specific TSH intervals, and TSH was positively associated with TC and low-density lipoprotein cholesterol (LDL-C). In the 71-80 and > 80 age groups, the prevalence of high TC, high triglycerides (TGs), and high LDL-C increased significantly with elevated TSH reference ranges. The levels of TC, TGs, and LDL-C were also positively associated with TSH level in 71-80 age group. However, such an association disappeared in > 80 age group. An age-specific reference range for TSH can effectively prevent the overdiagnosis of SCH in the elderly. Aging could somewhat attenuate the impact of TSH on lipid profiles.

Investigation of the effect of boron on thyroid functions and biochemical parameters in hypothyroid induced-rats

In the study investigating the effects of boron on thyroid hormones and some biochemical parameters in hypothyroid rats, 49 Wistar Albino male rats were divided into seven groups; (Control (C), Hypothyroidism (H), boron groups (B10, and B20), hypothyroid + boron groups (HB10 and HB20), and Treatment (T). Four groups (H, HB10, HB20, and T) were administered 10 mg/kg (B10 and HB10), 20 mg/kg (B20 and HB20) boron for 3 weeks, respectively after hypothyroidism was induced using Propycil® containing propylthiouracil (PTU). Thyroid hormone analyses and biochemical measurements were made from the serum and thyroid gland tissue was examined histopathologically. According to the findings, the fT3 level increased in the B10 group compared to the control group (p < 0.05). While AST, ALT, and ALP activities were found to be higher in the hypothyroid group than in the control group, AST and ALP activities in the HB10 and HB20 groups decreased to values close to the control group. Total cholesterol levels were found to be lower in boron-given groups compared to control and hypothyroid groups (p < 0.05). Sodium iodide symporter (NIS) immunoreactivity was found to be high in hypothyroid rat groups. As a result, it was observed that the increased AST and ALP activities in rats decreased with boron administration. The serum hormone levels measured in the study are not sufficient to understand the effect of boron on the thyroid gland, and it was concluded that further studies at the molecular level are needed to understand the effects of boron on the thyroid gland.

Carotid Beta Stiffness Association with Thyroid Function

Background: Thyroid hormone modulation of cardiovascular function has been associated with cardiovascular disease. Recent evidence suggests that free thyroxine (FT4) levels are associated with an increase in systemic arterial stiffness, but little is known about the effects of FT4 at the local level of the common carotid artery. β-stiffness index is a local elastic parameter usually determined by carotid ultrasound imaging. Methods: We conducted a cross-sectional analysis in the ProgeNIA cohort, including 4846 subjects across a broad age range. For the purpose of this study, we excluded subjects with increased thyrotropin (TSH) levels and those treated with levothyroxine or thyrostatic. We assessed β stiffness, strain, wall–lumen ratio, carotid cross-sectional area (CSA), and stress and flow in the right common carotid artery. We tested whether FT4, heart rate, and their interactions were associated with carotid parameters. Results: FT4 was positively and independently associated with β stiffness index (β = 0.026, p = 0.041), and had a negative association with strain (β = −0.025, p = 0.009). After adding heart rate and the interaction between FT4 and heart rate to the model, FT4 was still associated with the β stiffness index (β = 0.186, p = 0.06), heart rate was positively associated with the stiffness index (β = 0.389, p < 0.001) as well as their interaction (β = 0.271, p = 0.007). Conclusion: This study suggests that higher FT4 levels increase arterial stiffness at the common carotid level, consistent with a detrimental effect on elastic arteries. The effect of FT4 is likely to be primarily attributable to its effect on heart rate.

No association between subclinical hypothyroidism and dyslipidemia in children and adolescents

Background

There are controversies about the correlation between higher levels of thyroid stimulating hormone (TSH) and dyslipidemia in children. This study was designed to assess the relation between lipid profile components and TSH levels in children.

Method

This cross-sectional study was performed in a pediatric endocrinology growth assessment clinic in Shiraz, southern Iran. Children aged 2–18 years who referred to the clinic from January until April 2018 were included. TSH levels equal or above 5 mIU/L and lower than 10 mIU/L with normal free T4 (FT4) were considered as having subclinical hypothyroidism (SH).

Results

Six hundred sixty-six children were euthyroid while 181 had SH. No significant difference was found between the mean serum total cholesterol (P = 0.713), LDL-C (P = 0.369), HDL-C (P = 0.211), non-HDL-C (P = 0.929), and triglyceride (P = 0.215) levels between euthyroid children and subjects with SH. There was also no significant difference in the prevalence of dyslipidemias in any lipid profile components between the two groups. The adjusted correlation was not significant between TSH levels and any lipid profile component.

Conclusion

Based on the results of our study, we found no correlation between SH and dyslipidemia in children. The association between dyslipidemia and SH in children still seems to be inconsistent based on the results of this and previous studies. We recommend a meta-analysis or a significantly larger retrospective study on this subject.

Effect of rhTSH on Lipids

BACKGROUND

Subclinical hypothyroidism is associated with increased blood lipid levels. However, the exact role of thyrotropin (TSH) alone is not clear. In order to clarify this point, we analysed the acute effect of recombinant human TSH (rhTSH) administration on lipid levels.

METHODS

Sera of 27 premenopausal women with well-differentiated thyroid cancer were analysed. Patients that underwent a total thyroidectomy, ablation with ¹³¹I (Iodine 131) and rhTSH administration as a part of routine follow-up American Thyroid Association guidelines were included. The protocol consists of 2 intramuscular injections of 0.9 mg of rhTSH, performed on day 1 day and day 2, with blood collection on day 1 (before rhTSH administration), and day 5. TSH, free thyroxine, total cholesterol, low-density lipoprotein cholesterol (LDLc), high density lipoprotein cholesterol (HDLc), and triglycerides were assessed in all the samples, before and four days after the first administration of rhTSH.

RESULTS

Total cholesterol and triglycerides significantly increased after stimulation of rhTSH (respectively, 192 ± 33 vs. 207 ± 26, p = 0.036 and 72 ± 23 vs. 85 ± 23, p = 0.016). LDLc and HDLc showed comparable concentrations before and after the test (respectively, 115 ± 27 vs. 126 ± 22, p = 0.066, and 62 ± 15 vs. 64 ± 15, p = 0.339), while non-HDLc increased after stimulation (130 ± 30 vs. 143 ± 25, p = 0.045).

CONCLUSION

TSH has a direct effect on total cholesterol, triglycerides, and nonHDLc. Explanation of these phenomena will require additional studies.

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.

Reference intervals in the diagnosis of thyroid dysfunction: treating patients not numbers

Although assigning a diagnosis of thyroid dysfunction appears quite simple, this is often not the case. Issues that make it unclear whether thyroid function is normal include transient changes in thyroid parameters, inter-individual and intra-individual differences in thyroid parameters, age-related differences, and ethnic variations. In addition, a statistically calculated distribution of thyroid analytes does not necessarily coincide with intervals or cutoffs that have predictive value for beneficial or adverse health outcomes. Based on current clincial trial data, it is unclear which individuals with mild thyroid-stimulating hormone elevations will benefit from levothyroxine treatment. For example, only a small number of patients with thyroid-stimulating hormone values of more than 10 mIU/L have been studied in a randomised manner. Even if therapy is initiated for abnormal thyroid function, not all treated individuals are maintained at the desired treatment target, and therefore might still be at risk. The consequence of this is that each patient's thyroid function needs to be assessed on an individual basis with the entire clinical picture in mind. Monitoring also needs to be vigilant, and the targets for treatment reassessed continually.

Role of Adipokines in the Association between Thyroid Hormone and Components of the Metabolic Syndrome

Metabolic syndrome (MS) increases cardiovascular risk. The role of thyroid hormone on components of MS is unclear. We analyzed a sample of 4733 euthyroid subjects from SardiNIA study. In female thyrotropin (TSH) was significantly and positively associated with triglycerides (Standardized regression coefficients (β) = 0.081, p < 0.001). Free thyroxine (FT4) was positively associated with HDL (β = 0.056, p < 0.01), systolic blood pressure (SBP) (β = 0.059, p < 0.001), diastolic blood pressure (DBP) (β = 0.044, p < 0.01), and fasting glucose (β = 0.046, p < 0.01). Conversely, FT4 showed a negative association with waist circumference (β = −0.052, p < 0.001). In TSH was positively associated with triglycerides (β = 0.111, p < 0.001) and FT4 showed a positive association with DBP (β = 0.51, p < 0.01). The addition of leptin and adiponectin to the regression models did not substantially change the impact of thyroid hormones on components of MS. Our data suggest that, even within the euthyroid range, excess of truncal adipose tissue is associated with variations in FT4. Leptin and adiponectin exert an additive effect rather than a causal effect. Additional studies should be performed to determine the clinical significance of this finding.

Association Between Thyroid Dysfunction and Lipid Profiles Differs According to Age and Sex: Results from the Korean National Health and Nutrition Examination Survey

BACKGROUND

Lipid profiles of men and women change differently during the aging process. Guidelines recommend that dyslipidemia patients should consider screening for hypothyroidism without consideration of age or sex.

METHODS

Data from the sixth Korean National Health and Nutrition Examination Survey were used. A total of 4275 participants without thyroid disease and without a past history of dyslipidemia or dyslipidemia medication were evaluated. The association between thyroid dysfunction and lipid profiles (total cholesterol [TC], low-density lipoprotein cholesterol [LDLC], and triglycerides [TG]) was analyzed by age and sex.

RESULTS

The prevalence of thyroid dysfunction was significantly different according to TC and LDLC levels (p = 0.003 and p = 0.021, respectively). In women, the weighted prevalence of thyroid dysfunction was significantly different according to levels of TC, LDLC, and TG (p = 0.007, p = 0.016, and p = 0.044, respectively). However, in men, no association was found in any of the lipid profiles. Female participants were divided into two groups using a cutoff age of 55 years. In younger women, the weighted prevalence of thyroid dysfunction was different according to the levels of TC, LDLC, and TG (p = 0.013, p = 0.007, and p = 0.007, respectively). However, in older women, no association was found for any of the lipid profiles.

CONCLUSIONS

The prevalence of thyroid dysfunction was significantly different according to lipid profiles, and this association differed by age and sex.

Thyrotropin Levels Are Associated with Cardiometabolic Risk Factors in Euthyroid Adolescents

BACKGROUND

Increased thyrotropin (TSH) levels and free triiodothyronine to free thyroxine (fT3:fT4) ratios, even within the euthyroid range, have been associated with cardiometabolic risk factors in adults but are less characterized in youth. This study sought to determine relations between TSH, thyroid hormones, and cardiometabolic risk factors in euthyroid adolescents.

METHODS

Data were extracted from the United States National Health and Nutrition Examination Survey, 2007-2010, for univariate and multivariate analyses of TSH, thyroid hormones, body mass index (BMI), blood pressure, lipids, and glucose metabolism. Subjects aged 12-18 years, with normal TSH and antithyroid peroxidase antibody levels, and without a history of thyroid disease, diabetes, or treatment of hypertension/dyslipidemia (n = 1167) were included. TSH and thyroid hormones were assessed for impact on BMI Z-score, systolic blood pressure (SBP) diastolic blood pressure, total cholesterol (TC), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoprotein B, triglycerides, and glucose metabolism.

RESULTS

Univariate analyses revealed positive linear relations between TSH and SBP, TC, fasting and two-hour glucose, and homeostasis model assessment of insulin resistance (HOMA-IR). The fT3:fT4 ratio negatively correlated with high-density lipoprotein cholesterol but positively with BMI Z-score, SBP, triglycerides, fasting and two-hour glucose, fasting insulin, and HOMA-IR. In multivariate analyses controlling for age, sex, race/ethnicity, and BMI Z-score, relations between TSH and both TC and fasting glucose remained significant, and the fT3:fT4 ratio was positively associated with fasting glucose and HOMA-IR.

CONCLUSIONS

In an unselected population of euthyroid U.S. adolescents, TSH and thyroid hormones correlate with multiple cardiometabolic risk factors, with age- and sex-independent effects on cholesterol and glucose metabolism.

Menopause modulates the association between thyrotropin levels and lipid parameters: The SardiNIA study

OBJECTIVE

Thyroid hormone influences lipoprotein metabolism. The role of menopausal status in this association has not been extensively studied. The aim of the present study is to evaluate the association between lipid parameters and mild elevations of thyrotropin (TSH), and whether menopause influences this relationship.

STUDY DESIGN

A cross-sectional study was conducted with a sample of 2,914 women (aged 14-102 years) from the SardiNIA study.

MAIN OUTCOME MEASURES

The association of TSH with blood lipid levels was examined using regression analyses, according to menopausal status.

RESULTS

Postmenopausal women had lower serum TSH concentrations and higher levels of total cholesterol, low-density lipoprotein cholesterol (LDLc), high-density lipoprotein cholesterol (HDLc), and triglycerides than did premenopausal women (p=0.001 or less for all). In premenopausal women, after adjusting for the confounders age, BMI, smoking, insulin and glycaemia, TSH showed a direct relation to the levels of total cholesterol (β=0.046, p=0.010), LDLc (β=0.044, p=0.016) and triglycerides (β=0.085, p<0.001), but no association with HDLc level. In the postmenopausal group, TSH was directly associated only with triglyceride levels (β=0.103, p=0.014).

CONCLUSIONS

The association between mild elevation of TSH and lipid levels is influenced by menopausal status. Further research is needed to clarify this finding.

L-Arginine Derivatives Are Associated with the Hyperthyroid State in the General Population

BACKGROUND

Arginine (ARG) derivatives and thyroid function independently influence atherosclerotic processes. Since thyroid hormones may mediate the association between ARG derivatives and atherosclerosis, this study investigated whether asymmetric and symmetric dimethylarginines (ADMA and SDMA, respectively) as well as homoarginine (hARG) are associated with parameters of thyroid function in the general population.

METHODS

Cross-sectional data from 3689 individuals aged 20-81 years from the population-based Study of Health in Pomerania (SHIP-0) were analyzed. Thyroid function was defined according to serum concentrations of thyrotropin (TSH), free triiodothyronine (fT3), and free thyroxine (fT4). Low and high serum TSH were defined by the cutoffs 0.3 mIU/L and 3 mIU/L, respectively. Serum concentrations of ARG, ADMA, SDMA, and hARG were measured using liquid chromatography-tandem mass spectrometry. ARG, ADMA, SDMA, and hARG were associated with serum concentrations of TSH, fT3, and fT4 by median regression and with categorized TSH values by multinomial logistic regression adjusted for age, sex, smoking status, physical activity, body mass index, and estimated glomerular filtration rate.

RESULTS

Levels of ADMA (relative risk [RR] = 5.40 [confidence interval (CI) 1.96-14.86]) and SDMA (RR = 3.55 [CI 1.01-12.70]) were associated with low TSH. In addition, ADMA (β = 0.38 [CI 0.23-0.45]) was positively associated with fT3, while both ADMA (β = 0.98 [CI 0.43-1.54]) and SDMA (β = 1.19 [CI 0.50-1.88]) were positively associated with fT4. No consistent associations of ARG and hARG with thyroid function were detected.

CONCLUSIONS

The positive associations of ADMA and SDMA with low TSH, fT3, and fT4 argue for a relationship of arginine derivatives with increased thyroid function. This suggests that the atherogenic properties of ADMA and SDMA may be partially mediated by thyroid function.

Relationship between thyroid hormones, resting energy expenditure and cardiometabolic risk factors in euthyroid subjects

BACKGROUND & AIMS

Whereas hypothyroid subjects have a decreased resting energy expenditure (REE), it is unknown whether REE is associated with TSH in euthyroid subjects. It is also uncertain whether there is an association between cardiometabolic risk factors and TSH among euthyroid subjects. The primary aim was to test whether REE and TSH are associated in euthyroid subjects. The second aim was to evaluate the association between TSH and cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure.

METHODS

885 Caucasian euthyroid subjects (75% women) aged 18-79 years and with a median body mass index of 28.6 kg/m(2) were consecutively studied at our Research Center. REE was measured using a canopy-equipped indirect calorimeter. Multivariable regression of 25(th), 50(th) and 75(th) percentiles was used to evaluate the association between the outcomes (REE, cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure) and the predictors (TSH, FT4 and FT3) controlling by gender, age and body mass index.

RESULTS

REE was not associated with TSH, FT4 and FT3 at any percentile. On the contrary, a positive association between TSH and triglycerides was evident at all percentiles. A positive association between FT3 and HDL-cholesterol was also present but only at the 75(th) percentile.

CONCLUSIONS

REE is not associated with TSH in euthyroid subjects. It is however positively associated with triglycerides confirming the findings of recent population studies.