Subclinical hypothyroidism and hyperthyroidism have opposite effects on hepatic very-low-density lipoprotein-triglyceride kinetics

Serum Lipidomic Analysis Reveals Biomarkers and Metabolic Pathways of Thyroid Dysfunction

Abnormal thyroid hormone secretion is the most important feature of hypothyroidism and plays an important role in lipid metabolism. However, their connection has not been clearly established. This study aimed to identify the serum biomarkers and metabolic pathways associated with hyperthyroidism and hypothyroidism. The study enrolled discovery and validation sets of 175 and 300 participants, respectively, to identify and validate the serum biomarkers of hyperthyroidism and hypothyroidism via ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry lipidomics through univariate and multivariate analyses. Eight and six biomarkers were identified for hyperthyroidism and hypothyroidism, respectively. Spearman correlation analysis was used to assess the correlation between the biomarkers and thyroid dysfunction indicators; subsequently, metabolic pathway and network analyses were performed for these biomarkers. Most biomarkers exhibited significant correlation with thyroid dysfunction indicators, mainly being enriched in the glycerophospholipid (GPL) metabolism. The diagnostic accuracies of the biomarkers and biomarker panels were assessed via receiver operating characteristic curve analysis. All the biomarkers demonstrated good diagnostic performance, and the hyperthyroidism and hypothyroidism biomarker panels reached an area under the curve value of 1.000. The results were validated using the validation set. Therefore, our findings revealed that thyroid dysfunction primarily affects the human metabolism via the GPL metabolism, thus providing a theoretical basis for the clinical prevention and control of thyroid dysfunction.

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.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

SUBCLINICAL HYPOTHYROIDISM AS A CONTRIBUTOR TO MACROVASCULAR COMPLICATIONS IN PATIENTS WITH TYPE 2 DIABETES MELLITUS

This study aimed to evaluate changes of the lipid panel data in patients with comorbid type 2 diabetes mellitus (T2DM) and subclinical hypothyroidism (SCH) and to identify the probable prognostic values of the lipid profile for macrovascular complication (MVC) development. The study included 370 patients presented with only T2DM and 30 patients suffering from both T2DM and SCH. Receiver operating characteristic (ROC) analysis was used to identify prognostically significant values of the lipid profile with the optimal ratio of sensitivity and specificity for MVC development. All lipid profile values in the patients with T2DM combined with SCH were significantly higher compared to those with only T2DM. At the same time, SCH + T2DM increased the risk of exceeding target levels of triglycerides by 2.9 times and HDL-C by 4.1 times. Analysis of lipid profile values according to macrovascular involvement showed that total cholesterol, LDL-C and non-HDL-C in patients with T2DM and SCH were significantly higher compared to those with only T2DM. The levels of triglycerides >1.65 mmol/L, non-HDL-C >3.74 mmol/L and remnant cholesterol >0.74 mmol/L determined by the ROC analysis can be used for stratification of patients with T2DM combined with SCH into the category of increased risk of MVC development.

Retrospective study of the influence of hypothyroidism on liver function before radioiodine therapy in China: a comparison analysis based on patients with differentiated thyroid cancer

PURPOSE

The aim of the present study is to investigate the risk factors for hepatic dysfunction before radioiodine therapy in patients with differentiated thyroid cancer (DTC).

METHODS

996 patients (314 men, 682 women; age of 45.07±12.98 years) with postoperative DTC were recruited and divided into two groups including patients with and without hepatic dysfunction. The changes in baseline data and traced liver function levels, together with other metabolic profiles, were compared between the two groups.

RESULT

Overall, 31.6% of patients had hepatic dysfunction. Higher aspartate aminotransferase and/or alanine aminotransferase was the most common abnormality (the prevalence rate was 47.5%). The percentages of mild and moderate hepatic dysfunction were 80.0% and 20.0%, respectively. Univariate analyses demonstrated that the most prominent risk factors for hepatic dysfunction (OR=0.324-3.171, p<0.01) were male sex with levothyroxine discontinuation and free triiodothyronine <2.01 pmol/L, free thyroxine (FT₄) <4.78 pmol/L, thyroid-stimulating hormone >78.195 µIU/mL, total cholesterol >5.17 mmol/L, triglycerides (TG) >1.71 mmol/L and more than 21 days of thyroid hormone withdrawal. Multivariate analyses demonstrated that for men, FT₄ <3.80 pmol/L and TG ≥1.28 mmol/L were the most prominent risk factors.

CONCLUSIONS

Patients with minor hepatic dysfunction and ortholiposis are more likely to recover to normal liver function. Patients with moderate hepatic dysfunction should be treated with hepatoprotective drugs. For men, FT₄ and TG levels tended to be associated with hepatic dysfunction, and the prognosis of hepatic dysfunction was closely related to the TG level.

CORRELATION BETWEEN SUBCLINICAL HYPOTHYROIDISM AND DYSLIPIDEMIA IN WOMEN IN NORTHEAST CHINA

CONTEXT

It is well known that thyroid hormones are important, being involved in affects the metabolism of carbohydrate, protein, lipids. The relationship between thyroid hormones and lipid metabolism is the focus of recent research.

OBJECTIVE

To investigate the relationship between subclinical hypothyroidism and lipid metabolism in women.

DESIGN

We conducted an epidemiological survey of thyroid diseases among women in Northeast China from September 2014 to December 2014.

SUBJECTS AND METHODS

A total of 1397 women underwent physical examinations and laboratory tests for thyroid function and lipid metabolism.

RESULTS

We found that the detection rate of subclinical hypothyroidism was 13.03%. Patients with subclinical hypothyroidism showed significantly higher levels of triglyceride (1.69±1.9 vs. 1.45±1.4) and the risk of hyper triglyceridemia in women with thyroid stimulating hormone (TSH) levels ≥10mIU/L was 4.96-fold higher compared with that in the normal population (P<0.01).

CONCLUSION

Disorders of lipid metabolism in women with subclinical hypothyroidism show a direct correlation with the level of TSH, and the risk of hyper triglyceridemia is significantly increased when the level of TSH ≥10mIU/L.

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.

Relationship between TSH Levels and the Advanced Lipoprotein Profile in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

The relationship between thyroid-stimulating hormone (TSH) and lipoprotein subfractions by Vertical Auto Profile (VAP) is unclear. We aimed to evaluate lipoprotein profiles according to TSH levels in euthyroid individuals.Material and Methods: Cross-sectional analysis of 3,525 participants from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) with no previous thyroid disease and who were not on lipid-lowering medication. Total-cholesterol and its fractions, lipoprotein subfractions, triglycerides, and triglyceride-rich lipoprotein cholesterol [TRL-C (VLDL₁₊₂-C, VLDL₃-C, IDL-C)] were determined by VAP. Associations between TSH quintiles and lipoprotein subfractions were evaluated by crude and adjusted linear regression models.Results: For the total sample, significant beta-coefficients in full adjusted models for the 5^th quintile of TSH (compared to 1^st) were found for the following VAP lipids and lipoproteins: IDL-C (β: 0.90; 0.11 to 1.69); VLDL-C (β: 2.80; 1.51 to 4.08), triglycerides (β: 18.66; 8.07 to 29.25), non-HDL-C (β: 4.63; 0.50 to 8.75 mg/dl), TRL-C (β:1.93;0.70 to 3.17), VLDL₃-C (β: 1.04; 0.50 to 1.57), as well as, TC/HDL-C (β: 0.15; 0.03 to 0.26) and TG/HDL-C ratio (β: 0.49;0.21 to 0.77). In women, similar results were found for VLDL-C, triglycerides, non-HDL-C, TRL-C, VLDL₃-C, TC/HDL-C and TG/HDL-C-ratios. In men, we also found positive associations between the highest quintile of TSH with VLDL-C, triglycerides, VLDL₃-C and TG/HDL-C.Conclusions: In the ELSA-Brasil, the highest TSH levels were mostly positively associated with lipoprotein levels, particularly TG, TRL and their remnants. Notwithstanding, our findings suggest that TSH levels within the normal range have little impact on the atherogenic profile.

A Population-Based Cohort Study on the Association of Hyperthyroidism With the Risk of Hyperlipidemia and the Effects of Anti-thyroid Drugs on Hepatic Gene Expression

There have been no reports on the association of hyperthyroidism with hyperlipidemia in patients undergoing treatment especially in Asia. To determine the association between hyperthyroidism and the risk of hyperlipidemia in patients, we conducted a retrospective cohort study using Longitudinal Health Insurance Database (LHID) from Taiwan, R.O.C. We also evaluate the influence of 6-n-propyl-2-thiouracil (PTU) and methimazole (MMI) on hepatic genes to explain changes in blood lipid levels in a hepatic cell line model. The cohort study involved 13,667 patients with hyperthyroidism, and the corresponding comparison cohort had four times as many patients. Using Kaplan-Meier analysis method, the results showed that, compared to patients without hyperthyroidism, the overall incidence of hyperlipidemia was significantly higher in the hyperthyroidism patients (18.7 vs. 11.8 cases/1,000 persons-years; adjusted HR 1.5; 95% CI, 1.41–1.59). With only PTU or MMI/carbimazole (CBM) treatment, patients with hyperthyroidism showed a 1.78-fold (95% CI, 1.50–2.11) and 1.43-fold (95% CI, 1.27–1.60) higher risk of hyperlipidemia than those without hyperthyroidism, respectively. Additionally, hyperthyroidism patients that received surgery only or surgery with I¹³¹ therapy tended to have a higher risk of hyperlipidemia. Although PTU and MMI treatment decreased the expression levels of genes responsible for circulating remnant lipoproteins, they increased the levels of lipogenic gene expression in hepatic cells. Thus, treatment of hyperthyroid patients with anti-thyroid drugs (ATDs), I¹³¹, or surgery is likely to induce hyperlipidemia. ATDs downregulate the expression of genes involved in lipoproteins clearance; increases lipogenic genes expression, which may partly contribute to abnormal blood lipid profiles.

Pathogenesis of hypothyroidism-induced NAFLD: Evidence for a distinct disease entity?

Nonalcoholic fatty liver disease (NAFLD), the most common liver disease worldwide, may be associated with primary hypothyroidism. However, the pathogenesis underlying such an association is complex and not completely understood. Here, we specifically discuss the pathogenic mechanisms potentially involved in hypothyroidism-induced NAFLD. To this end, we summarize the general pathophysiology of thyroid hormones (TH). Next, we analyze the published data from rodent studies by discussing whether hypothyroid rats may develop NAFLD via hyperphagia; whether mitochondria become energetically more efficient; what the overall energy balance is and if diversion of fatty substrates occurs; and the latest advancements in molecular pathogenesis brought about by metabolomics, cell imaging, lipophagy, autophagy and genetically engineered mouse models. Moreover, we discuss the data published regarding humans on the pathogenic role of TH, metabolic syndrome and other risk factors in hypothyroidism-related NAFLD as well as the putative mechanisms underlying the development of NAFLD-related hepatocellular carcinoma in hypothyroidism. In conclusion, although many research questions still remain unanswered, the pathophysiology of hypothyroidism-induced NAFLD makes this a potentially curable and distinct disease entity. However, further studies are needed to better elucidate the underlying mechanisms, and to ascertain whether treatment with either TH or thyromimetic agents improves NAFLD.

Hypothyroidism and nonalcoholic fatty liver disease - a chance association?

Background Nonalcoholic fatty liver disease (NAFLD) defines the clinical-pathological spectrum of hepatic lipotoxicity, which may progress to hepatic fibrosis and its complications. Thyroid hormone is a master regulator of cell metabolism and body fat distribution. Whether hypothyroidism is associated or not with an increased risk of developing NAFLD and its fibrotic progression is both clinically and physiopathologically relevant. Indeed, answering this research question would carry major pathogenic and therapeutic implications. Method PubMed database was searched using relevant key-words such as hypothyroidism; NAFLD; nonalcoholic steatohepatitis; cirrhosis; hepatocellular carcinoma; epidemiology; pathogenesis; natural history. The epidemiological studies and the meta-analyses published so far were identified as well as those studies addressing the physiopathology underlying this association. Results Many observational studies have investigated the association between either subclinical or overt hypothyroidism and NAFLD. Data are conflicting: some original and meta-analytical studies demonstrated that hypothyroidism, (mainly subclinical hypothyroidism), was common, occurring in approximately 25% of individuals with imaging-defined or biopsy-proven NAFLD; other studies, however, failed to identify a significant association between hypothyroidism and NAFLD. Moreover, such an association is biologically plausible based on the specific physiopathological impact of thyroid hormone and thyroid stimulating hormone (TSH) on metabolism of hepatocytes and accumulation and distribution of body fat. Conclusions The findings from the present review support a significant association between primary hypothyroidism and risk of development and progression of NAFLD. However, further studies evaluating the relative importance of subclinical versus overt hypothyroidism as well as addressing the mechanisms underlying the association of hypothyroidism with NAFLD are eagerly awaited.

A Renewed Focus on the Association Between Thyroid Hormones and Lipid Metabolism

Thyroid dysfunction, manifesting as either overt or subclinical hypothyroidism, negatively affects lipid metabolism: this leads to hypercholesterolemia which progressively increases the risk for cardiovascular disease and, potentially, mortality. Hypercholesterolemia in hypothyroidism is mainly due to a reduction in low-density lipoprotein (LDL) receptor activity, this accompanied by concomitant diminishing control by triiodothyronine (T3) of sterol regulatory element-binding protein 2 (SREBP-2), which modulates cholesterol biosynthesis by regulating rate-limit degrading enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA) activity. Recently, 3,5-diiodothyronine (T2), a natural thyroid hormone derivative, was found to repress the transcription factor carbohydrate-response element-binding protein (ChREBP) and also to be involved in lipid catabolism and lipogenesis, though via a different pathway than that of T3. While thyroid hormone could therapeutically reverse the dyslipidemic profile commonly occurring in hypothyroidism, it should be borne in mind that the potency of the effects may be age-and sex-dependent. Thyroid hormone administration possibly also sustains and enhances the efficacy of hypolipidemic drugs, such as statins, ezetimibe and proprotein convertase subtilisin/kexin type 9 (PCSK9), in patients with dyslipidemia and hypothyroidism.

Higher free triiodothyronine is associated with non-alcoholic fatty liver disease in euthyroid subjects: the Lifelines Cohort Study

OBJECTIVE

Overt hypothyroidism confers an increased risk of non-alcoholic fatty liver disease (NAFLD). The liver plays a crucial role in the metabolism of cholesterol and triglycerides; thyroid hormones interact on hepatic lipid homeostasis. Thyroid function within the euthyroid range affects a number of health issues, including atherosclerosis development and biochemical markers of increased cardiovascular risk. However, the association of thyroid hormones with NAFLD in euthyroid subjects has not been unequivocally established. We therefore determined associations of thyroid hormone parameters with NAFLD among euthyroid subjects.

METHODS

The study was conducted in the Lifelines Cohort Study, a population-based cohort study of participants living in the North of the Netherlands. Only euthyroid subjects (thyroid-stimulating hormone (TSH) 0.5-4.0mU/L, free thyroxine (FT4) 11-19.5pmol/L and free triiodothyronine (FT3) 4.4-6.7pmol/L) older than 18years were included. Exclusion criteria were participants with excessive alcohol use, known hepatitis or cirrhosis, liver functions ≥ three times the upper limit, current cancer, non-white ancestry, previous or current use of thyroid medication and current use of lipid or glucose lowering medication. A priori defined liver biochemistry, thyroid function parameters and metabolic syndrome (MetS) were studied. NAFLD was defined by using the validated Fatty Liver Index (FLI); FLI≥60 was categorized as NAFLD. A P<0.01 was considered significant.

RESULTS

FLI≥60 was found in 4274 (21.1%) of 20,289 individuals (62.1% male, median age 46years) with increased prevalence of MetS (P<0.0001). In age- and sex-adjusted analysis FLI≥60 was independently associated with a higher FT3 (OR 1.34, 95% CI 1.29-1.39, per SD increment, P<0.0001) and a lower FT4 (OR 0.73, 95% CI 0.70-0.75, P<0.0001) but not by TSH. The strongest association was found for the FT3/FT4 ratio (OR 1.44, 95% CI 1.39-1.49, P<0.0001). These associations remained similar after additional adjustment for the presence of MetS. In subjects with enlarged waist circumference, TSH and FT4 were lower while FT3 was higher, resulting in an increased FT3/FT4 ratio (P<0.0001).

CONCLUSIONS

Euthyroid subjects with suspected NAFLD are characterized by higher FT3, lower FT4 and higher FT3/FT4 ratio, probably consequent to central obesity.

Relationship between Hypothyroidism and Non-Alcoholic Fatty Liver Disease: A Systematic Review and Meta-analysis

BACKGROUND

Previous studies propose that hypothyroidism might play a crucial role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD), but findings from published studies on the relationship between hypothyroidism and NAFLD are still controversial. Our study aimed to make a comprehensive evaluation of the relationship between hypothyroidism and NAFLD through a meta-analysis.

METHODS

PubMed, China Dissertation Database, and EMBASE databases were searched to find observational studies assessing the relationship between hypothyroidism and NAFLD. The pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated to evaluate the strength of the relationship between hypothyroidism and NAFLD through meta-analysis.

RESULTS

Thirteen articles were ultimately included in our meta-analysis. Meta-analysis of the 13 studies found a high correlation between hypothyroidism and NAFLD (OR = 1.52, 95% CI 1.24-1.87, P < 0.001). Meta-analysis of 9 studies providing adjusted ORs found that hypothyroidism was independently correlated with NAFLD (OR = 1.72, 95% CI 1.32-2.23, P < 0.001). Subgroup analysis found that both overt hypothyroidism and subclinical hypothyroidism were significantly correlated with NAFLD, and the pooled ORs were 1.70 (95% CI 1.23-2.36, P = 0.002) and 1.40 (95% CI 1.10-1.77, P = 0.006), respectively. Besides, meta-analysis of studies providing adjusted ORs also found that both overt hypothyroidism and subclinical hypothyroidism were independently correlated with NAFLD, and the pooled ORs were 1.81 (95% CI 1.30-2.52, P < 0.001) and 1.63 (95% CI 1.19-2.24, P = 0.002), respectively.

CONCLUSION

The meta-analysis provides strong epidemiological evidence for the relationship between hypothyroidism and NAFLD. Both individuals with subclinical and overt hypothyroidism are at higher risk for NAFLD than euthyroid subjects.

Histopathologic Evaluation of Nonalcoholic Fatty Liver Disease in Hypothyroidism-Induced Rats

It is speculated that thyroid hormones may be involved in nonalcoholic fatty liver disease (NAFLD) pathogenesis. A literature scan, however, demonstrated conflicting results from studies investigating the relationship between hypothyroidism and NAFLD. Therefore, our study aims to evaluate NAFLD, from the histopathologic perspective, in hypothyroidism-induced rats. Wistar rats were divided into 2 groups: the experimental group consumed water containing methimazole 0.025% (MMI, Sigma, USA) for 12 weeks and the control group consumed tap water. At the end of week 12, serum glucose, ALT, AST, triglyceride, HDL, LDL, TSH, fT4, fT3, visfatin, and insulin assays were performed. Sections were stained with hematoxylin-eosin and "Oil Red-O" for histopathologic examination of the livers. In our study, we detected mild hepatosteatosis in all hypothyroidism-induced rats. There was statistically significant difference with respect to obesity between the two groups (p < 0.001). The mean fasting blood glucose was 126.25 ± 23.4 mg/dL in hypothyroidism-induced group and 102.63 ± 15.51 mg/dL in the control group, with a statistically significant difference between the groups (p = 0.032). The two groups did not differ statistically significantly with respect to visfatin levels (p > 0.05). In conclusion, we found that hypothyroidism-induced rats had mild hepatosteatosis as opposed to the control group histopathologically. Our study indicates that hypothyroidism can cause NAFLD.

Cardiovascular Risk in Patients with Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) has been associated with increased cardiovascular mortality due to adverse effects mainly on lipids and blood pressure (BP). There is evidence that SCH, especially in patients with thyroid-stimulating hormone (TSH) >10mU/l, may increase cardiovascular risk. Some uncertainty exists regarding the association of SCH with BP; however, that the coexistence of SCH with BP and hypercholesterolaemia has a negative cardiovascular impact is beyond doubt. Insulin resistance, by modulating various risk factors including coagulation, may potentially increase cardiovascular risk. Periodic health examinations including screening has been advised in patients >35 years of age, while treatment with thyroxine should be tailored to each patient.

Triiodothyronine and free thyroxine levels are differentially associated with metabolic profile and adiposity-related cardiovascular risk markers in euthyroid middle-aged subjects

BACKGROUND

We have previously shown that in healthy young men, a less favorable body composition is associated with higher free triiodothyronine (fT3) levels within the euthyroid range. Besides, a higher free-triiodothyronine-to-free-thyroxin (fT3-to-fT4) ratio has been related to a less favorable metabolic phenotype and more placental growth in pregnant women. In the present study, we therefore investigated whether serum thyrotropin (TSH), thyroid hormone levels, and the fT3-to-fT4 ratio are associated with metabolic and adiposity-related cardiovascular risk markers in a healthy population of middle-aged euthyroid men and women.

METHODS

Thyroid parameters were measured in 2524 generally healthy subjects from the Asklepios Study (35-55 years, mean age 46 years). Analyses were restricted to 2315 subjects (1138 women and 1177 men), not using thyroid medication, not having anti-TPO levels above clinical cutoff values or TSH levels outside the reference range (0.27-4.2 mU/L). Twenty-seven percent of the women and 47.5% of the men were overweight, while 13% of women and 17% of men were obese. Twenty percent of the subjects were active smokers. Serum thyroid function parameters were determined by electrochemiluminescence.

RESULTS

fT3 and the fT3-to-fT4 ratio were positively related to body mass index (BMI), waist circumference, and components of metabolic syndrome, that is, triglycerides, systolic and diastolic blood pressure, and fasting plasma glucose, and negatively with HDL-cholesterol levels, whereas fT4 was negatively associated with BMI, waist circumference, and triglycerides (p<0.001). TSH related positively with total cholesterol levels (p<0.01), triglycerides, and systolic and diastolic blood pressure (p<0.001). The fT3-to-fT4 ratio was further positively associated with the adiposity-related inflammation markers interleukin-6 and high-sensitivity C-reactive protein and to pulse wave velocity. All associations were adjusted for sex, age, height, and smoking, and most associations persisted after additional adjustment for weight or waist circumference.

CONCLUSION

In healthy euthyroid middle-aged men and women, higher fT3 levels, lower fT4 levels, and thus a higher fT3-to-fT4 ratio are consistently associated with various markers of unfavorable metabolic profile and cardiovascular risk.

Dyslipidemia and serum mineral profiles in patients with thyroid disorders

OBJECTIVES

To investigate changes in serum lipid profile, levels of serum minerals associated with thyroid disorders, and to compare these with the serum lipid and mineral profiles in hypothyroid patients receiving thyroxine therapy.

METHODS

A cross-sectional study was conducted in King Khaled Hospital, Hail, Saudi Arabia. The patient database was searched for new patients with thyroid dysfunction between January 2011 and June 2012. They were classified into 5 groups: 1) subclinical-hypothyroid (SHY), 2) overt-hypothyroid (OHY), 3) subclinical-hyperthyroid (SHE), 4) overt-hyperthyroid (OHE), 5) patients under thyroxine therapy (EU), and normal controls.

RESULTS

The OHY group showed impaired renal function; whereas, the kidney function of the SHE, OHE, and EU groups was normal. The OHY and OHE groups exhibited elevated serum glucose. The OHY group showed elevated serum cholesterol, triglyceride, and low-density lipoprotein cholesterol, and decreased high-density lipoprotein cholesterol. Serum lipids were reduced in the OHE group, and no different in the EU group compared with controls. The serum calcium and phosphate were reduced in the OHY group, whereas, in the OHE group, the phosphate was increased while magnesium and potassium were reduced.

CONCLUSION

Hypothyroidism caused impaired renal function, glucose intolerance, hyperlipidemia, and reduction in serum phosphate. Hyperthyroidism caused a reduction in serum lipids, magnesium, and potassium. Thyroxine therapy normalized the deranged lipids and minerals, but not glucose. RESULTS indicate that thyroid function tests should be considered when diagnosing those metabolic disorders. 

Subclinical hypothyroidism and indices for metabolic syndrome in Japanese women: one-year follow-up study

CONTEXT

Subclinical hypothyroidism (SCH) and metabolic syndrome (MetS) increase with age; however, their relationship remains unclear.

OBJECTIVE

Our objective was to investigate the relationship between SCH and indices of metabolic syndrome and follow up subjects for 1 year.

DESIGN

Cross-sectional and longitudinal follow-up studies of cases were collected from Takasaki Hidaka Hospital between 2003 and 2007.

PARTICIPANTS

Overall, 11 498 participants of health checkups were analyzed. The mean age was 48 ± 9 years.

MAIN OUTCOME MEASURES

The relationship between SCH and indices of MetS were examined.

RESULTS

Serum free T4 levels were lower in women than men in most of the age groups, and the prevalence of SCH, 6.3% in women vs 3.4% in men, increased with age, reaching 14.6% in 70-year-old women. Multivariate logistic-regression analyses revealed that waist circumference and the serum triglyceride and low-density lipoprotein-cholesterol levels were significantly higher in subjects with SCH than without among women. Reflecting these findings, the adjusted odds ratio of MetS in patients with SCH was higher than in the euthyroid subjects in women with an odds ratio of 2.7 (95% confidence interval 1.1-5.6; P = .017) but not in men. Furthermore, progression from euthyroid into SCH resulted in a significant increase in the serum triglyceride levels but not low-density lipoprotein-cholesterol in women.

CONCLUSION

Japanese women exhibited a high prevalence of SCH associated with low free T4 levels. There was a strong association between SCH and several indices of metabolic syndrome in women. SCH may affect serum triglyceride levels and be a risk factor for metabolic syndrome.