Hypothyroidism and Lipid Levels in a Community Based Study (TTS)

Hypothyroidism and Cardiovascular Disease: A Review

Hypothyroidism is an endocrine disorder more commonly in older adults. Simultaneously, this population has an increased incidence of cardiovascular risk factors and disease, which remains the leading cause of death worldwide. Thyroid hormones (THs) promote adequate function of the cardiovascular system as they exert their effects through receptors located in the myocardium and the vasculature. In hypothyroidism, this homeostasis is disrupted, which leads to the emergence of pathogenic pathways that accelerate the progression of cardiovascular disease and aggravate its outcomes in these individuals. This article has reviewed existing literature on the relationship between hypothyroidism and cardiovascular disease (CVD). We have explored the pathogenic mechanisms linking both conditions and highlighted the prevalence of cardiovascular risk factors as well as the increased incidence of cardiovascular events in overt and subclinical diseases. Furthermore, indications of hormone replacement therapy in subclinical disease and its efficacy in reducing CVD morbidities in a particular subset of patients have been discussed.

The correlation of lipid profile with subclinical and overt hypothyroidism: A cross-sectional study from Syria

We proceeded with this study to investigate the relationship between hypothyroidism and lipid profile disturbance. A cross-sectional study at Al- Mowasat University Hospital in Damascus was conducted from March 2021 to March 2022, and included 324 adults. For each participant with abnormal thyroid stimulating hormone (TSH), free thyroxine (FT4) was requested. The participants were categorized into 3 groups: euthyroid (226 participants), subclinical hypothyroidism (SCH) (75 participants), and overt hypothyroidism (23 participants). Fasting lipid profile was tested as: cholesterol (Chol), triglycerides (TG), low density lipoprotein (LDL), and high density lipoprotein (HDL). A significant relationship between hypothyroidism and dyslipidemia was noticed. LDL, TG, and Chol but not HDL showed a significant difference between study groups (euthyroidism, subclinical, and overt hypothyroidism). The lowest levels of these parameters were in euthyroidism and increased in subclinical and overt hypothyroidism subsequently. Overt hypothyroidism showed a significant difference in LDL, TG, and Chol compared to euthyroidism, however, we did not find a difference in lipid parameters in SCH compared to euthyroidism. LDL and Chol showed significant differences between subclinical and overt hypothyroidism. TSH had a positive weak correlation with LDL, TG, and Chol, however, there was no correlation with HDL. Also, FT4 had a negative weak correlation with LDL, TG, and Chol, however, there was a positive correlation with HDL. Our findings suggest a higher level of lipids (LDL, TG, and Chol) among SCH and overt hypothyroidism compared to general population. A weak correlations of lipid parameters with TSH and FT4 were detected. It is not well evident whether a restoration of euthyroidism might influence the morbidity and mortality, especially cardiovascular comorbidities, in this population, which mandates future studies.

A study of cardiovascular profile in patients with primary hypothyroidism

Introduction and Aim: Raised cardiovascular morbidity is common among patients with primary hypothyroidism. Study of electrocardiogram (ECG) and echocardiography (ECHO) and correlation with lipid profile may help in early detection of cardiovascular diseases in hypothyroidism. By this study, we aimed at studying the cardiovascular profile in patients with primary hypothyroidism and correlating ECHO and ECG changes in primary hypothyroidism with the LDL cholesterol.  Materials and Methods: This was a single centre cross-sectional observational study. All patients diagnosed with primary hypothyroidism were included. The laboratory parameters pertaining to primary hypothyroidism were recorded. ECG and ECHO were noted and correlated with lipid profile.   Results: Total 240 subjects were selected according to inclusion and exclusion criteria, of which males were 25% and females 75%. Mean ± SD of LDL-C among subjects having ST-T changes was 160.98 ±14.86. Mean ± SD of LDL-C among subjects having no ST-T changes was 128±10.15. Unpaired student t test was used to compare mean of lipid profile in patient having ST-T changes with patients having no ST-T changes. A strong correlation was observed between LDL cholesterol and ST-T changes in ECG (P value =0.001) Conclusion: Diastolic dysfunction is more common than systolic dysfunction in primary hypothyroidism. LDL levels were high in patients with primary hypothyroidism who had ST-T changes in electrocardiogram. Levothyroxine replacement causes decrease in Total as well as LDL cholesterol in primary hypothyroidism. ECG changes correlated with abnormal lipid profile in patients with primary hypothyroidism.  

Hypothyroidism correlates with dyslipidemia and protein contents in patients with various metabolic disorders

OBJECTIVES

The present study aimed to investigate the status of abnormalities in thyroid-related hormones, lipid profile parameters and total proteins in the sera of patients suffering from various metabolic disorders.

METHODS

To analyze the study parameters, enzyme-linked immunosorbent assays, Bradford assays and standard clinical kits and methods were applied. Data were analyzed through the appropriate statistical tests.

RESULTS

In all subjects except those with hypotension, thyroid-stimulating hormone, total cholesterol and low-density lipoprotein were elevated, whereas triiodothyronine levels were downregulated. Thyroxin was downregulated in subjects with diabetes and symptomatic thyroiditis but upregulated in patients with hypertension. High-density lipoprotein was upregulated in men who were diabetic only, and total protein was downregulated in those with hypotension only. Hypothyroidism in patients with diabetes, symptomatic thyroiditis and hypertension was correlated with dyslipidemia. In subjects with hypertension, it was correlated with total protein.

CONCLUSION

This study revealed a link between hypothyroidism, dyslipidemia and total protein in patients with various metabolic disorders.

Comparative Study of Calculated LDL-Cholesterol Levels with the Direct Assay in Patients with Hypothyroidism

Background Hypothyroidism is one among the many factors that predisposes one to coronary artery disease. As low-density lipoprotein-cholesterol (LDL-C) is associated with cardiovascular risk, calculated LDL-C should have good accuracy with minimal bias. Hypothyroidism alters the lipid composition of lipoproteins by the secretion of triglyceride-rich lipoproteins, which affects the calculation of LDL-C. The present study aimed to compare 13 different formulae for the calculation of LDL-C including the newly derived Martin's formula by direct assay in patients of hypothyroidism.

Method In this analytical cross-sectional study, a total of 105 patients with laboratory evidence of hypothyroidism, from January to June 2019, were studied, and blood samples were subjected for lipid profile analysis at central biochemistry laboratory. Calculated LDL-C was assessed by different formulae.

Result We observed that calculated LDL-C by Friedewald's, Cordova's, Anandaraja's, Hattori's, and Chen's formulae has bias less than ± 5 compared with direct LDL-C, with Anandaraja's formula having the lowest bias (2.744) and Cordova's formula having lowest bias percentage (−1.077) among them. According to the Bland–Altman plots, the bias in Friedewald's and Anandraja's were equally distributed below and above the reference line of direct LDL-C.

Conclusion This is the first study comparing different formulae for LDL-C calculation in patients with hypothyroidism. Anandaraja's formula was as equally effective as Friedewald's formula when used as an alternative cost-effective tool to evaluate LDL-C in hypothyroid patients. The recently proposed Martin's formula for calculated LDL-C had a higher bias when compared with Friedewald's and Anandaraja's formulae in patients with hypothyroidism.

Thyroid disorders and cardiovascular manifestations: an update

Cardiovascular disease (CVD) remains the leading cause of death worldwide, representing a major health, social, and economic issue. Thyroid disorders are very common and affect >10% of the adult population in total. The aim of this review is to describe the physiologic role of thyroid hormones on cardiovascular system, to present cardiovascular manifestations in patients with thyroid disorders, emphasizing in molecular mechanisms and biochemical pathways, and to summarize current knowledge of treatment options. Thyroid hormone receptors are located both in myocardium and vessels, and changes in their concentrations affect cardiovascular function. Hyperthyroidism or hypothyroidism, both clinical and subclinical, without the indicated therapeutical management, may contribute to the progression of CVD. According to recent studies, even middle changes in thyroid hormones levels increase cardiovascular mortality from 20% to 80%. In more details, thyroid disorders seem to have serious effects on the cardiovascular system via plenty mechanisms, including dyslipidemia, hypertension, systolic and diastolic myocardial dysfunction, as well endothelial dysfunction. On top of clinical thyroid disorders management, current therapeutics focus on younger patients with subclinical hypothyroidism and elderly patients with subclinical hyperthyroidism.

Lipid profile in mild subclinical hypothyroidism: systematic review and meta-analysis

INTRODUCTION

Only severe subclinical hypothyroidism (SSCH) with TSH above 10 mIU/L is considered a risk factor of hyperlipidemia and cardiovascular disease. The results of published papers on mild subclinical hypothyroidism (MSCH) with TSH below10 mIU/L are contradictory. The objective of the study was to conduct a systematic review and meta-analysis on lipid profiles in a population of patients with MSCH (TSH10> mIU/L and normal T3, T4) in comparison with euthyroid subjects.

EVIDENCE ACQUISITION

The electronic databases PubMed, CIANHL, Scopus, and Web of Science were searched systematically between August 20, 2018 and September 15, 2018, without limitation on the date of publication or the language. Titles, abstracts and articles were reviewed to identify papers that evaluated lipid profiles in patients with MSCH compared to euthyroid.

EVIDENCE SYNTHESIS

A systematic review of the studies and a meta-analysis using R software (version 3.6.1) were performed. Thirty-five case control and cohort studies were included in the meta-analysis. Total cholesterol (TC), low density lipoprotein (LDL), and triglycerides (TG) were significantly higher and high-density lipoprotein (HDL) was significantly lower in MSCH patients compared to euthyroid individuals. Mean differences (MD) [95% CI] were 12.75 [6.02, 19.48], 10.95 [6.37, 15.54], 19.27 [10.90, 27.64], and -1.81 [-3.38, -0.23], respectively. No significant difference was observed for very low-density lipoproteins (VLDL), apolipoprotein A1 (apoA1), or apolipoprotein B (apoB). The studies were of fair to good quality.

CONCLUSIONS

MSCH is associated with an increase in major atherogenic lipoproteins and should be viewed as a cardiovascular risk factor.

Comparative efficacy of early morning versus bedtime administration of levothyroxine in children with hypothyroidism: a prospective, open label, randomized, case-control study

INTRODUCTION

Studies in adults with hypothyroidism suggest an equal efficacy of bedtime versus early morning intake of levothyroxine. There is limited data on timing of levothyroxine administration in children.

MATERIAL AND METHODS

Children with hypothyroidism on early morning levothyroxine, and clinically and biochemically euthyroid, were assigned to receive levothyroxine at bedtime (group A) or were continued on early morning levothyroxine intake (group B). Clinical, anthropometric and laboratory evaluation (thyroid and lipid profiles, liver enzymes and creatinine) was done at baseline, and at 3 and 6 months.

RESULTS

Eighty-four children, 42 in each group, completed the study. The clinical and anthropometric parameters remained similar in the two groups at baseline and at 3- and 6-month follow-up visits. There was no difference in the mean serum concentrations of triiodothyronine, thyroxine and thyrotropin at the 3 time-points in the study. In addition, mean serum aspartate transaminase, alanine transaminase, creatinine and parameters of lipid profiles remained similar in the two groups. The requirement of levothyroxine was similar at baseline (48.6 ±16.9 µg vs. 49.6 ±19.5 µg, p-value 0.80) and at the endpoint (48.3 ±17.2 µg vs. 51.9 ±18.0 µg, p-value 0.46) in both groups. At the study end, 25 (60%) patients in group A and 17 (40%) in group B preferred bedtime dosing of levothyroxine.

CONCLUSIONS

We found an equal efficacy of bedtime intake compared to early morning intake of levothyroxine in maintaining an euthyroid state in children with hypothyroidism. Further studies are required to see if bedtime levothyroxine administration improves the quality of life of patients.

gp91phox, a Novel Biomarker Evaluating Oxidative Stress, Is Elevated in Subclinical Hypothyroidism

BACKGROUND

gp91^phox, the catalytic core of NADPH oxidase (NOX) and biomarker of NOX activation, has been recently recognized as a parameter of systemic oxidative stress in several studies. Subclinical hypothyroidism (SH) is characteristic of elevated level of serum thyroid stimulating hormone (TSH) and is frequently accompanied with cholesterolemia. In this study, the levels of serum soluble gp91^phox were measured to assess the oxidative stress in patients with SH. And the relationship among gp91^phox, low-density lipoprotein-C (LDL-C), and TSH was also investigated.

METHODS

A total of 51 subjects were enrolled and categorized into four groups: the healthy controls subjects (n = 13), controls with high level of LDL-C alone (n = 12), SH with normal level of LDL-C (n = 11), and SH with high level of LDL-C (n = 15). The related clinical and laboratory data were collected for statistical analysis. All the patients were newly diagnosed and did not take any medication. The information of lipid profile and thyroid function was extracted, and the concentrations of gp91phox were obtained with ELISA.

RESULTS

The levels of serum soluble gp91phox evidently increased in the patients with SH with a high level of LDL-C (81.52 ± 37.00 ug/mL) as compared to the healthy controls (54.98 ± 1.83ug/mL, p < 0.001), controls with high level of LDL-C (61.21 ± 4.48 ug/mL, p=0.038) and SH with a normal level of LDL-C (62.82 ± 11.67ug/mL, p=0.027). Additionally, the levels of gp91^phox showed a significant positive correlation with both the levels of LDL-C (r = 0.595, p < 0.001) and TSH (r = 0.346, p=0.013) by the Spearman correlation analyses. The correlation remained significant even when the effect of another factor was controlled (TSH: when the effect of LDL-C was controlled, r = 0.453, p=0.001; LDL-C: when the effect of TSH was controlled, r = 0.291, p=0.040). The main effect analysis showed an independent main effect of either LDL-C (p = 0.041) or TSH (p=0.022) on gp91^phox without interaction (p=0.299).

CONCLUSIONS

Our work demonstrated that the levels of gp91^phox, a novel biomarker for measuring the oxidative stress, were significantly elevated in the patients with SH. And LDL-C and TSH were both independent predictors of gp91^phox. Abbreviations. BMI : Body mass index; TC : Total cholesterol; LDL-C : Low-density lipoprotein cholesterol; HDL-C : High-density lipoprotein cholesterol; TG : Triglyceride; FBG : Fasting blood glucose; FT3 : Free triiodothyronine; FT4 : Free thyroxine; TSH: Thyroid stimulating hormone; SBP : Systolic blood pressure; DBP : Diastolic blood pressure; SD : Standard deviation; LSD: Least significant difference.

Exercise training-induced changes in metabolic syndrome parameters, carotid wall thickness, and thyroid function in middle-aged women with subclinical hypothyroidism

This study analyzed the differences in effects of a 12-week combination of exercise training program with resistance training and aerobic exercises on the risk factors of metabolic syndrome, carotid wall thickness, and thyroid function, between subclinical hypothyroidism patients and obese groups, in middle-aged women. Subjects consisted of either 20 middle-aged women in the subclinical hypothyroidism (SCH) group or 20 obese (body mass indices [BMI], ≥ 25 kg/m²) women without hypothyroidism in the obese (OB) group. The body composition, blood lipid factors, hormones associated with thyroid functions, blood pressure (BP), and carotid intima-media thickness were measured, while physical fitness was ascertained. In the SCH group, waist circumference (WC) and high-density lipoprotein cholesterol values were outside the normal ranges, while WC and systolic BP (SBP) were outside the normal ranges in the OB group. Following the 12-week training program, significantly positive changes occurred in body fat percentage, sit and reach test results, and SBP (p < 0.05) in the SCH group, while in the OB group, significantly positive changes in BMI, WC, sit and reach test results, SBP, and diastolic BP (DBP, p < 0.05) were observed. In addition, both groups showed significant decreases in intima-media thickness of the right carotid bifurcation (p < 0.05). However, in the two groups, the 12-week exercise training program did not have similar significant impact on the hormones related to thyroid functions and blood lipids. Therefore, further research on exercise training that can effectively induce changes in the hormones associated with thyroid functions in patients with subclinical hypothyroidism is necessary.

Association of metabolic risks with subclinical hypothyroidism: A cross-sectional analysis

Objective:

To compare lipid parameters, HbA1c, uric acid and albumin creatinine ratio (UACR) among subjects having euthyroidism, Sub-Clinical Hypothyroidism (SCH) and overt hypothyroidism.

Methods:

This comparative cross-sectional analysis was carried out from Dec-2015 to Oct-2016 in collaboration between PNS HAFEEZ hospital and department of chemical pathology and endocrinology, Armed Forces Institute of Pathology, Rawalpindi. Biochemical parameters including lipid indices, HbA1c and UACR were compared between euthyroidism (TSH: 0.5 to 4.0 mIU/L, n=163), subclinical hypothyroidism (TSH: 4.0 to 10 mIU/L, n=16) and overt hypothyroidism (TSH:≥ 10.0 mIU/L, n=9).

Results:

LDL-cholesterol, non-HDL-cholesterol and UACR results were as: [(Euthyroid: 2.66 ± 0.73), (SCH: 2.68 ± 0.51) and (Overt hypothyroidism: 3.23 ± 0.59), p-value=0.063], [(Euthyroid: 3.49 ± 0.64), (SCH: 3.35 ± 0.59) and (Overt hypothyroidism: 4.01 ± 0.30), p-value=0.033] and [{Euthyroid: 2.48 (95% CI: 1.63-3.33)}, {SCH: 2.27 (95% CI: 0.37-4.90)} and {Overt hypothyroidism: 14.95 (95% CI: 10.71-19.14){, (p-value< 0.001)] Results for total cholesterol, triglycerides and HDL-cholesterol though increased in overt hypothyroid group were not found to be statistically significant.

Conclusion:

LDL-cholesterol, non-HDL-cholesterol and UACR increased from euthyroid subjects to overt hypothyroidism group. However, these changes were found to be more subtle in the subclinical hypothyroid subjects than cases with overt hypothyroidism.

Thyroid function and ischemic heart disease: a Mendelian randomization study

To clarify the role of thyroid function in ischemic heart disease (IHD) we assessed IHD risk and risk factors according to genetically predicted thyroid stimulating hormone (TSH), free thyroxine (FT4) and thyroid peroxidase antibody (TPOAb) positivity. Separate-sample instrumental variable analysis with genetic instruments (Mendelian randomization) was used in an extensively genotyped case (n = 64,374)-control (n = 130,681) study, CARDIoGRAMplusC4D. Associations with lipids, diabetes and adiposity were assessed using the Global Lipids Genetics Consortium Results (n = 196,475), the DIAbetes Genetics Replication And Meta-analysis case (n = 34,380)-control (n = 114,981) study, and the Genetic Investigation of ANthropometric Traits (body mass index in 152,893 men and 171,977 women, waist-hip ratio in 93,480 men and 116,741 women). Genetically predicted thyroid function was not associated with IHD (odds ratio (OR) per standard deviation for TSH 1.05, 95% confidence interval (CI) 0.97 to 1.12; for FT4 1.01, 95% CI 0.91 to 1.12; for TPOAb positivity 1.10, 95% CI 0.83 to 1.46) or after Bonferroni correction with risk factors, except for an inverse association of FT4 with low-density lipoprotein-cholesterol. The associations were generally robust to sensitivity analyses using a weighted median method and MR Egger. This novel study provides little indication that TSH, FT4 or TPOAb positivity affects IHD, despite potential effects on its risk factors.