Is thyroid-stimulating hormone within the normal reference range a risk factor for atherosclerosis in women?

Increased thyroid stimulating hormone (TSH) as a possible risk factor for atherosclerosis in subclinical hypothyroidism

Primary hypothyroidism (PHT) is associated with an increased risk for the development of atherosclerosis (AS) and other cardiovascular disorders. PHT induces atherosclerosis (AS) through the induction of endothelial dysfunction, and insulin resistance (IR). PHT promotes vasoconstriction and the development of hypertension. However, patients with subclinical PHT with normal thyroid hormones (THs) are also at risk for cardiovascular complications. In subclinical PHT, increasing thyroid stimulating hormone (TSH) levels could be one of the causative factors intricate in the progression of cardiovascular complications including AS. Nevertheless, the mechanistic role of PHT in AS has not been fully clarified in relation to increased TSH. Therefore, in this review, we discuss the association between increased TSH and AS, and how increased TSH may be involved in the pathogenesis of AS. In addition, we also discuss how L-thyroxine treatment affects the development of AS.

Hypothyroidism, lipids, and lipidomics

PURPOSE

Hypothyroidism is a relatively common endocrine disorder and is well documented to be associated with lipid abnormalities.

METHODS

A narrative review was conducted of studies describing the alterations in the lipid profile accompanying both subclinical and overt hypothyroidism.

RESULTS

Lipid abnormalities are seen with TSH values in the upper end of the accepted reference range, as well as with subclinical and overt hypothyroidism. The degree of lipid derangement is generally proportional to the degree of TSH elevation. Other factors such as age, sex, and body mass index can also influence the pattern of the lipid abnormalities seen. The most robust finding with TSH elevation is increases in the low density lipoprotein cholesterol. Thyroid hormone treatment is efficacious in reversing the lipid abnormalities in both subclinical and overt hypothyroidism.

CONCLUSION

Given the association of lipid abnormalities with metabolic and cardiovascular disease, consideration of hypothyroidism as an important non-communicable disease may facilitate studies that test the hypothesis that thyroid hormone treatment to reverse hypothyroidism-associated lipid abnormalities may improve metabolic and cardiovascular outcomes.

Thyrotropin induces atherosclerosis by upregulating large conductance Ca2+-activated K+ channel subunits

Hypothyroidism is associated with elevated levels of serum thyrotropin (TSH), which have been shown to promote abnormal proliferation of vascular smooth muscle cells and contribute to the development of atherosclerosis. However, the specific mechanisms underlying the TSH-induced abnormal proliferation of vascular smooth muscle cells remain unclear. The objective of this study was to investigate the role of TSH in the progression of atherosclerosis. Our research findings revealed that hypothyroidism can trigger early atherosclerotic changes in the aorta of Wistar rats. In alignment with our in vitro experiments, we observed that TSH induces abnormal proliferation of aortic smooth muscle cells by modulating the expression of α and β1 subunits of large conductance Ca2+-activated K+ (BKCa) channels within these cells via the cAMP/PKA signaling pathway. These results collectively indicate that TSH acts through the cAMP/PKA signaling pathway to upregulate the expression of α and β1 subunits of BKCa channels, thereby promoting abnormal proliferation of arterial smooth muscle cells. These findings may provide a basis for the clinical prevention and treatment of atherosclerosis caused by elevated TSH levels.

Prognostic Value of Normal Thyroid Stimulating Hormone in Long-Term Mortality in Patients With STEMI

BACKGROUND

Although within the normal range, thyroid stimulating hormone (TSH) levels are associated with cardio-metabolic disorders and have an effect on the cardiovascular system. The aim of our study was to assess the prognostic value of normal TSH on long-term mortality in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS

Consecutive STEMI patients who had a TSH level within the normal range (0.55-4.78 μIU/ml) were enrolled from November 2013 to December 2018. Patients were stratified into three groups depending on the tertile of TSH level, and all-cause mortality and cardiac death were compared. TSH concentrations associated with risk of all-cause mortality were evaluated in a continuous scale (restricted cubic splines) and the Cox proportional hazards regression model.

RESULTS

A total of 1,203 patients with STEMI were eligible for analysis. During a median follow-up of 39 months, patients in the 3rd tertile group had higher all-cause mortality (20.1% vs. 12.2% and 14.3%, p = 0.006) and cardiac death (15.4% vs. 7.7% and 12.3%, p = 0.001) as compared to the 1st and 2nd tertile groups. The Cox proportional hazards model showed that TSH was an independent predictor on long-term all-cause mortality (HR: 1.248, 95% CI: 1.046-1.490, p = 0.014). However, subgroup analysis indicated that TSH (HR: 1.313, 95% CI: 1.063-1.623, p = 0.012) was only significantly associated with long-term all-cause mortality in the patients without emergency reperfusion therapy. Restricted cubic spline analyses showed a linear relationship between TSH concentrations and all-cause mortality (P for non-linearity = 0.659).

CONCLUSIONS

A Higher TSH level - even in a normal range is associated with long-term mortality in patients with STEMI, proposing an additional indication to identify STEMI patients with poor prognosis.

The Association of Thyroid Hormones with Coronary Atherosclerotic Severity in Euthyroid Patients

The aim of the work was to explore the correlation between thyroid hormones and coronary atherosclerotic severity. This cross-sectional study included 340 euthyroid patients who underwent diagnostic coronary artery angiography (CAG). Gensini Score (GS) was applied to assess the severity of coronary atherosclerosis. Thyroid hormones and routine biochemical parameters were measured. The associations between thyroid hormones and coronary atherosclerosis severity were analyzed. Thyroid hormones levels or parameters were taken as both continuous variables and tertiles into analysis, and the lowest tertile was usually used as the reference (OR=1) for medium and highest tertiles. Free triiodothyronine (FT3) level was associated with GS≥22 (Median GS) in Model I adjusted for age and sex [Continuous: OR=0.46, 95% CI (0.23, 0.92), p=0.029; Tertile 3: OR=0.54, 95% CI (0.30, 0.97), p=0.038], and Model II adjusted for all known risk factors of coronary artery disease (CAD) [Continuous: OR=0.44, 95% CI (0.20, 0.95), p=0.036; Tertile 3: OR=0.49, 95% CI (0.25, 0.96), p=0.039]. Subjects with highest tertile of FT3 to free thyroxine (FT4) ratio (FT3/FT4 ratio) appeared to have the remarkably decreased risk of CAD in both Non-adjusted Model [OR=0.49, 95% CI (0.24, 0.98), p=0.044] and Model I [OR=0.45, 95% CI (0.22, 0.93), p=0.031]. Higher FT3 level within normal range was independently and negatively associated with severity of coronary atherosclerosis. Besides, FT3/FT4 ratio was remarkably correlated with the prevalence of CAD in euthyroid population.

Lower normal free thyroxine is associated with a higher risk of metabolic syndrome: a retrospective cohort on Chinese population

BACKGROUND

Recently, the relationship between thyroid hormones (THs) across the euthyroid ranges and metabolic syndrome (MetS) has been widely discussed. This study aimed to present specific cutoff values of THs to assess the association between THs and MetS in a euthyroid cohort.

METHODS

Data of 2694 subjects, aged 18-80 years, who attended health examination in Xi'an Electric Power Central Hospital from April 2011 to December 2015 were collected and analyzed. The first cohort enrolled 929 participants (followed up by 2221 person-years totally) to assess correlations between serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4) levels and MetS. The second cohort included 698 participants (followed up by 1709 person-years totally) to evaluate relationships between serum free triiodothyronine (FT3), free thyroxine (FT4) levels and MetS. MetS was defined according to the criteria of the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) scientific statements of 2009. Euthyroidism was defined as serum TSH, FT3 and FT4 levels within the reference ranges without taking any thyroid medication.

RESULTS

The cutoff values for TSH, T3, T4, FT3 and FT4 were 2.0mIU/L, 1.9 nmol/L, 117 nmol/L, 4.3 pmol/L and 16 pmol/L, respectively. Participants were categorized into two groups according to cutoff values: the lower-THs group and the higher-THs group. There was no significant difference in the risk of MetS between two groups in TSH, T3, T4 and FT3. The incidence of MetS was significantly higher in lower-FT4 group than higher-FT4 group (1.00 vs 0.622 (0.458, 0.846), P = 0.002). The lower-FT4/higher-TSH group had the highest hazard ratios of MetS. (2.131vs 1.0 (1.380,3.291), P = 0.006).

CONCLUSIONS

Lower normal FT4 (FT4 ≤ 16.0 pmol/L) is an independent risk factor for MetS, and lower normal thyroid function (TSH > 2.0 mIU/L and FT4 ≤ 16.0 pmol/L) is associated with a higher risk of developing MetS.

High-normal thyroid-stimulating hormone in euthyroid subjects is associated with risk of mortality and composite disease endpoint only in women

INTRODUCTION

The aim of the study was to evaluate whether serum thyroid-stimulating hormone (TSH) within the normal range in euthyroid subjects (having normal free triiodothyronine (fT3) and thyroxine (fT4)) is related to the risk of overall mortality or a composite endpoint of death and nonfatal events.

MATERIAL AND METHODS

In 614 middle-aged adult hospital screenees, free of uncontrolled diabetes at baseline, the association of sex-specific TSH tertiles with death was prospectively assessed using Cox regression, with the composite endpoint assessed using logistic regression in adjusted analyses, stratified by gender.

RESULTS

In total, 64 deaths and additional incident nonfatal events in 141 cases were recorded at a mean 7.55 years' follow-up. Multivariable linear regression revealed TSH to be significantly associated among men with age (p = 0.006), but in women inversely with fT3 and fT4 (p < 0.001, and p = 0.024 respectively). In logistic regression analysis, adjusted for age, fT3, fT4, systolic blood pressure and serum total cholesterol, sex-specific baseline TSH tertiles were associated in men neither with the risk of death nor with composite endpoint. In contrast, in women, the highest compared with the bottom TSH tertile predicted the risk of composite endpoint (relative risk: 2.02, 95% CI: 1.07-3.82) and, much more strongly, the mortality risk, independently of fT4 increments.

CONCLUSIONS

The significant association of higher range of normal serum TSH in euthyroid middle-aged adults with the risk of death and nonfatal adverse outcomes in women alone cannot be accounted for by the action of thyroid hormone and is consistent with involvement of TSH in the pro-inflammatory state.

Associations between the levels of thyroid hormones and lipid/lipoprotein levels: Data from National Health and Nutrition Examination Survey 2007-2012

Data from National Health and Nutrition Examination Survey for the years 2007-2012 were used to investigate associations between thyroid hormones and lipid/lipoprotein levels for a representative sample of general US population aged ≥20 years. There were no statistically significant differences for adjusted high density lipoprotein levels among thyroid function groups, namely, subclinical hyperthyroid (SCHPR), clinical hyperthyroid (CHPR), euthyroid (EU), clinical hypothyroid (CHYP), and subclinical hypothyroid (SCHYP). For the general US population, positive associations for thyroid stimulating hormones (TSH) and negative associations for free thyroxine (FT4) levels were observed with total cholesterol (TC, p<0.01), apolipoprotein B (APOB, p<0.01), and triglycerides (TG, p<0.01). A 10% increase in TC levels was associated with a 2% increase in TSH levels and 0.8% decrease in FT4 levels. Among EU subjects, TG levels were positively correlated with TSH (p<0.01) and negatively correlated with FT4 (p<0.01). For CHYP subjects, TG levels were negatively correlated with TSH (p<0.01). For iodine deficient participants, low density lipoprotein levels (LDL) were lower for SCHPR when compared with EU or CHYP (p<0.01). TC levels were usually lower for SCHPR than for EU, CHYP, and SCHYP but the differences were not necessarily statistically significant. For all participants and for iodine replete participants, TG levels for SCHPR were lower than for CHYP (p<0.01). CHYP and SCHYP had higher levels of TG than other three thyroid function groups. APOB levels were lower for SCHPR than for EU and CHYP for all participants and for iodine replete participants (p<0.01). There was a positive association between the four quartiles of thyroid stimulating hormones and TC, TG, and APOB. There was also an inverse association between the quartiles of free thyroxine levels and LDL, TC, TG, and APOB.

Serum TSH levels are associated with cardiovascular risk factors in overweight and obese adolescents

OBJECTIVE

To investigate the relationship between serum thyrotropin (TSH), insulin resistance (IR), and cardiovascular risk factors (CRF) in a sample of overweight and obese Brazilian adolescents.

METHODS

A retrospective, longitudinal analysis of 199 overweight and obese pubescent adolescents was performed. The TSH and free T4 (fT4) levels, anthropometric measurements, and laboratory test results of these patients were analyzed.

RESULTS

27 individuals (13.56%) presented with TSH levels above the normal level (subclinical hypothyroidism [SCH]). Their waist circumference (WC) was significantly higher than those of euthyroid individuals. Serum TSH was positively correlated with the homeostasis model assessment of insulin resistance (HOMA-IR) index, triglycerides (TG) and high-density lipoprotein cholesterol (HDL-C). Using TSH and BMI as independent variables, TSH levels were shown to be independently related to HOMA-IR (p=0.001) and TG (p=0.007). Among euthyroid subjects, individuals with TSH values <2.5mIU/mL exhibited statistically significant decreases in waist-to-hip ratio, HDL-C levels, and HOMA-IR scores and a tendency toward lower WC values.

CONCLUSION

SCH in overweight and obese adolescents appears to be associated with excess weight, especially visceral weight. In euthyroid adolescents, there appears to be a direct relationship between TSH and some CRF. In conclusion, in the present sample of overweight and obese adolescents, TSH levels appear to be associated with IR and CRF.

Lower-normal TSH is associated with better metabolic risk factors: A cross-sectional study on Spanish men

BACKGROUND AND AIMS

Subclinical thyroid conditions, defined by normal thyroxin (T4) but abnormal thyroid-stimulating hormone (TSH) levels, may be associated with cardiovascular and metabolic risk. More recently, TSH levels within the normal range have been suggested to be associated with metabolic syndrome and cardiovascular risk. This work studies the linearity of the relationship between metabolic syndrome and TSH across the euthyroid range.

METHODS AND RESULTS

We studied 3533 male participants of the Aragon Workers' Health Study (AWHS) with normal TSH and free T4 levels, across quintiles of these variables, after adjusting for age, alcohol intake, and smoking. Compared with the lowest TSH quintile, the odds ratios for metabolic syndrome at the higher quintiles, which indicate lower thyroid function, were 1.34 (1.04, 1.73), 1.56 (1.21, 2.01), 1.57 (1.22, 2.03), and 1.71 (1.32, 2.21). The lowest free T4 quintile also showed an odds ratio of 1.49 (1.16, 1.90) with respect to the highest quintile. In addition, spline models showed departures from linearity: the risk of metabolic syndrome mostly increases at TSH values below the median (sample half-closest to subclinical hyperthyroidism). Interestingly, glucose also increases with TSH primarily below the median TSH, diastolic blood pressure shows similar changes across the entire TSH range, whereas body mass index, triglycerides, and high-density lipoprotein (HDL)-cholesterol change only at the highest normal TSH values, which are associated with lower free T4 concentration.

CONCLUSIONS

TSH and free T4 within the normal range are associated with the metabolic syndrome. The sample half-below the TSH median (with probably higher functional thyroid status) exhibited better metabolic and cardiovascular profiles.

Thyroid hormone levels and incident chronic kidney disease in euthyroid individuals: the Kangbuk Samsung Health Study

BACKGROUND

Overt and subclinical hypothyroidism are associated with higher levels of serum creatinine and with increased risk of chronic kidney disease (CKD). The prospective association between thyroid hormones and kidney function in euthyroid individuals,however, is largely unexplored.

METHODS

We conducted a prospective cohort study in 104 633 South Korean men and women who were free of CKD and proteinuria at baseline and had normal thyroid hormone levels and no history of thyroid disease or cancer. At each annual or biennial follow-up visit, thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxin (FT4) levels were measured by radioimmunoassay. The study outcome was incident CKD, defined as an estimated glomerular filtration rate (eGFR)<60 ml/min/1.73 m2 based on the Chronic Kidney Disease Epidemiology Collaboration creatinine equation.

RESULTS

After a median follow-up of 3.5 years, 1032 participants developed incident CKD.There was a positive association between high-normal levels of TSH and increased risk of incident CKD. In fully-adjusted models including baseline eGFR, the hazard ratio comparing the highest vs the lowest quintiles of TSH was 1.26 [95% confidence interval (CI) 1.02 to 1.55; P for linear trend=0.03]. In spline models, FT3 levels below 3 pg/ml were also associated with increased risk of incident CKD. There was no association between FT4 levels and CKD.

CONCLUSIONS

In a large cohort of euthyroid men and women, high levels of TSH and low levels of FT3, even within the normal range, were modestly associated with an increased risk of incident CKD.

Association of thyroid-stimulating hormone and cardiovascular risk factors

Thyroid hormone plays an important role in regulating the lipid and glucose metabolism. Previously, much attention has been drawn to define the pathophysiological relationship between thyroid dysfunction and the incidence of cardiovascular diseases (CVDs). While the conditions of overt hypothyroidism and subclinical hypothyroidism were both emphasized, the association between CVD risks and the deregulated circulating thyroid-stimulating hormone (TSH) level remains to be elucidated. Nevertheless, multiple TSH-mediated physiological adaptations, including alteration of the serum lipids, body mass index, blood pressure and insulin sensitivity, have led to the difficulty of clearly examining the association between the TSH level and CVD prevalence. The current review aims to 1) summarize the evidence for the role of thyroid dysfunction and TSH abnormality in CVD pathogenesis and 2) explore the possible underlying molecular mechanisms of TSH-mediated cardiovascular pathology in hopes of providing better therapeutic strategies for the patients with deregulated TSH.

The Lipid Parameters and Lipoprotein(a) Excess in Hashimoto Thyroiditis

Objective. The risk of atherosclerotic heart disease is increased in autoimmune thyroiditis, although the reason is not clear. Lipoprotein(a) (Lp(a)) excess has been identified as a powerful predictor of premature atherosclerotic vascular diseases. The aim of this study is to investigate the relationship between Lp(a) levels and thyroid hormones in Hashimoto patients. Method. 154 premenopausal female Hashimoto patients (48 patients with overthypothyroid (OH), 50 patients with subclinical hypothyroid (SH), and 56 patients with euthyroid Hashimoto to (EH)) were enrolled in this study. The control group consists of 50 age matched volunteers. In every group, thyroid function tests and lipid parameters with Lp(a) were measured. Lp(a) excess was defined as Lp(a) > 30 mg/dL. Results. Total-C, LDL-C, TG, and Lp(a) levels were increased in Hashimoto group. Total-C, LDL-C, and TG levels were higher in SH group than in the control group. Total-C and LDL-C levels were also higher in EH group compared to controls. Lp(a) levels were similar in SH and EH groups with controls. However, excess Lp(a) was more common in subclinical hypothyroid and euthyroid Hashimoto group than in the control group. Conclusion. The Total-C and LDL-C levels and excess Lp(a) were higher even in euthyroid Hashimoto patients. Thyroid autoimmunity may have some effect on Lp(a) and lipid metabolism.

Evaluation of biochemical, hematological, and thyroid function parameters in nondipper and dipper hypertensive patients

AIM OF THE STUDY

In this study we investigated the effects of biochemical, hematologic, and thyroid function parameters on the circadian rhythm of hypertensive patients whose 24-h ambulatory blood pressure was being followed.

METHODS

We studied the fasting glucose, urea, creatinine, uric acid, aspartate transaminase, alanine aminotransferase, gamma-glutamyl transferase, total protein, albumin, lipid profiles, sodium, potassium, hemoglobin, white blood cell count, platelet count, mean platelet volume, thyroid stimulating hormone, free thyroid hormone values obtained simultaneously with 24-h ambulatory blood pressure results, as documented in the case records of 470 patients.

PATIENTS

Of the patients, 398 were in the nondipper hypertensive group and 72 in the dipper hypertensive group. Differences in serum biochemical, hematologic, and thyroid function parameters were compared between the groups.

RESULTS

No statistically meaningful difference was detected between the age, gender, biochemical and hematologic parameters of the two groups. When the two were compared with respect to thyroid function tests, thyroid stimulating hormone levels in the nondipper hypertensive group were significantly higher, while free triiodothyronine and thyroxine levels were significantly lower.

CONCLUSIONS

Thyroid function disorders are associated with hypertension. However, there are not enough data on the effects of thyroid hormones particularly on the nighttime blood pressure decrease in hypertensive patients. Although the exact mechanism between low thyroid hormone levels and nondipping hypertension development is not known, relatively low thyroid hormone levels in the nondipper group may be related to the decrease in vein wall compliance, considering the vascular effect of overt hypothyroidism.

A high normal TSH level is associated with an atherogenic lipid profile in euthyroid non-smokers with newly diagnosed asymptomatic coronary heart disease

Background

Serum lipid profiles may be influenced by thyroid function, but the detailed mechanism remains unclear. Increasing evidence suggests that thyrotropin (TSH) may exert extra-thyroidal effects. The goal of this study was to evaluate the relationship between serum TSH levels and the lipid profiles in euthyroid non-smokers with newly diagnosed asymptomatic coronary heart disease (CHD).

Methods

This was a retrospective study of 406 euthyroid non-smokers (187 males and 219 females) with newly diagnosed asymptomatic CHD from 2004 to 2010 in Jinan, China. Lipid parameters and the levels of TSH, FT3, and FT4 were determined. Multiple linear regression analysis and Logistic regression analysis were used to assess the influence of TSH on the lipid profiles and the risks of dyslipidemia.

Results

The TSH level, even within the normal range, was positively and linearly correlated with total cholesterol (TC), non-high density lipoprotein cholesterol (non-HDL-C) and triglycerides (TG) (Beta = 0.173, 0.181 and 0.103, respectively, P < 0.01 in all). With 1 mIU/L rise of TSH, the levels of TC, TG and non-HDL-C will increase by 1.010, 1.064, and 1.062 mmol/L, respectively. The odds ratio of hypercholesterolemia and hypertriglyceridemia with respect to the serum TSH level was 1.640 (95% CI 1.199-2.243, P = 0.002) and 1.349 (95% CI 1.054-1.726, P = 0.017), respectively.

Conclusions

TSH levels were correlated in a positive linear manner with the TC, non-HDL-C and TG levels in euthyroid non-smokers with newly diagnosed asymptomatic CHD. TSH in the upper limits of the reference range might exert adverse effects on lipid profiles and thus representing as a risk factor for hypercholesterolemia and hypertriglyceridemia in the context of CHD.