A systematic review and meta-analysis investigating the relationship between metabolic syndrome and the incidence of thyroid diseases

A non-fasting marker of metabolic syndrome in a high-risk population

OBJECTIVE

The rising prevalence of metabolic syndrome among young adults has prompted studies of fasting triglyceride-glucose (TyG) index as a marker of insulin resistance. We aimed to evaluate metabolic syndrome in young adults using non-fasting TyG index and a high-risk genetic model, 22q11.2 microdeletion.

METHODS

We assessed metabolic syndrome and its components in 350 adults (50.6% female) aged 18-59 (median 27.7, IQR 22.5-38.1) years with typical 22q11.2 microdeletions. We used multivariable logistic regression and receiver operating characteristic (ROC) curves to evaluate the association of non-fasting TyG index with metabolic syndrome.

RESULTS

Non-fasting TyG index was significantly associated with metabolic syndrome (OR 3.23, 95% CI 2.27-4.59, p < 0.0001), independent of age, sex, BMI, and hypothyroidism. Non-fasting TyG index was positively correlated with number of metabolic syndrome components per individual. In this high-risk population, prevalence of metabolic syndrome was 21.7% (60/277) among young adults (18-39 years), and 45.2% (33/73, p < 0.0001) among middle-aged adults (40-59 years). Non-fasting TyG index ≥4.81 was an effective indicator of prevalent metabolic syndrome, with an area under the ROC curve of 0.83 (95% CI 0.78-0.88).

CONCLUSIONS

The results support non-fasting TyG index as a practical marker of metabolic syndrome, and by extension insulin resistance, encouraging future studies evaluating non-fasting TyG index in young adults as a predictor of cardiovascular disease later in life. The high prevalence of metabolic syndrome at a young age in 22q11.2 microdeletion demonstrates the potential value of this genetic high-risk population for future prospective studies, with animal and cellular models available.

Thyroid Hormones and Metabolism Regulation: Which Role on Brown Adipose Tissue and Browning Process?

Thyroid hormones (THs) are important modulators of many metabolic processes, being strictly associated with the control of energy balance, mainly through activities on the brain, white and brown adipose tissue, skeletal muscle, liver, and pancreas. In this review, the principal mechanisms of TH regulation on metabolic processes will be discussed and THs' relevance in metabolic disease progression will be evaluated, especially in the cardiovascular context and correlated diseases. Moreover, we will discuss THs' regulatory role on metabolic events in white and brown adipose tissue, with a special focus on the process of "browning", which consists of the gradual acquisition by white adipocytes of the physical and functional characteristics of brown adipocytes. The advancements in research on molecular mechanisms and proposed physiopathological relevance of this process will be discussed.

A Real-Life Study in Patients Newly Diagnosed with Autoimmune Hashimoto's Thyroiditis: Analysis of Asthenia as Admission Complaint

Background: Amid the large panel of autoimmune thyroid diseases, Hashimoto's thyroiditis (HT) represents a major point across multidisciplinary daily practice. When it comes to the clinical picture, particularly in regard to asthenia (also described as "fatigue" or "decreased energy"), the differential diagnosis is challenging, and a meticulous anamnesis should be backed up by focused lab investigations. Our objective was to analyze the thyroid panel in newly diagnosed patients with HT in relationship with the presence of asthenia as an admission complaint. Methods: This was a retrospective, multi-centric, real-life study conducted in secondary endocrine units (university hospitals) from July 2022 to July 2023. The exclusion criteria were COVID-19 infection; an active malignancy, etc. Results: The cohort (N = 120) included an asthenia group (AS, 49.2%) and a non-AS group of a similar age (49.3 ± 14.7 vs. 47.1 ± 14.8 y, p = 0.426). Headache was more frequent in the AS group (35.6% vs. 18%, p = 0.03). Thyroid function and HT-related antibodies assays were similar between the groups and show no correlation with serum total cholesterol and triglycerides, respectively. TSH levels did not vary among the age sub-groups (p = 0.701). One third of the studied population was affected by hypothyroidism (TSH > 4.5 μIU/mL), being seen at a higher rate in the AS (39%) vs. non-AS group (23%). Total cholesterol positively correlated with the patients' age (r = 0.180, p = 0.049) and triglycerides (N = 120; r = 0.324, p < 0.001), as found only in the non-AS group (r = 0.246, p = 0.006, respectively, r = 0.319, p < 0.001). Conclusions: The analysis of the AS vs. non-AS group pinpointed the fact that, in regard to daily practice, asthenia as an admission complaint seems less of an indicator of an underlying thyroid dysfunction or a higher level of serum antibodies against thyroid in patients without a full clinical picture of thyrotoxicosis or myxoedema.

Metabolic Syndrome, Thyroid Dysfunction, and Cardiovascular Risk: The Triptych of Evil

The triad formed by thyroid dysfunction, metabolic syndrome (MetS), and cardiovascular (CV) risk forms a network with many connections that aggravates health outcomes. Thyroid hormones (THs) play an important role in glucose and lipid metabolism and hemodynamic regulation at the molecular level. It is noteworthy that a bidirectional association between THs and MetS and their components likely exists as MetS leads to thyroid dysfunction, whereas thyroid alterations may cause a higher incidence of MetS. Thyroid dysfunction increases insulin resistance, the circulating levels of lipids, in particular LDL-C, VLDL-C, and triglycerides, and induces endothelial dysfunction. Furthermore, THs are important regulators of both white and brown adipose tissue. Moreover, the pathophysiological relationship between MetS and TH dysfunction is made even tighter considering that these conditions are usually associated with inflammatory activation and increased oxidative stress. Therefore, the role of THs takes place starting from the molecular level, then manifesting itself at the clinical level, through an increased risk of CV events in the general population as well as in patients with heart failure or acute myocardial infarction. Thus, MetS is frequently associated with thyroid dysfunction, which supports the need to assess thyroid function in this group, and when clinically indicated, to correct it to maintain euthyroidism. However, there are still several critical points to be further investigated both at the molecular and clinical level, in particular considering the need to treat subclinical dysthyroidism in MetS patients.

Obesity and Obesity-Related Thyroid Dysfunction: Any Potential Role for the Very Low-Calorie Ketogenic Diet (VLCKD)?

PURPOSE OF REVIEW

This review aims to explore in-depth the different aspects of the association between very low-calorie ketogenic diet (VLCKD), obesity and obesity-related thyroid dysfunction.

RECENT FINDINGS

The VLCKD, proposed as a non-pharmacological strategy for the management of certain chronic diseases, is becoming increasingly popular worldwide. Initially used to treat epilepsy, it has been shown to be effective in controlling body weight gain and addressing various pathophysiological conditions. Research has shown that a low-calorie, high-fat diet can affect thyroid hormone levels. Weight loss can also influence thyroid hormone levels. Studies have suggested that long-term use of VLCKD for refractory epilepsy may be related to the development of hypothyroidism, with an effect seen in various populations. In particular, women with obesity following VLCKD tend to have reduced T3 levels. We propose further research to unravel the underlying mechanisms linking VLCKD to obesity and obesity-related thyroid dysfunction.

Subclinical Hypothyroidism in Patients with Obesity and Metabolic Syndrome: A Narrative Review

The literature on the connection between obesity, metabolic syndrome, and subclinical hypothyroidism is critically analyzed in this narrative review. These conditions are frequently observed among adult populations and various studies and meta-analyses have assessed their association. The prevalence of subclinical hypothyroidism in obese individuals is higher than in non-obese subjects and this trend is more pronounced in unhealthy obesity phenotypes. However, the diagnosis and treatment of subclinical hypothyroidism can be difficult in obese patients. Exaggerated body fat is linked to thyroid hypoechogenicity as evident through ultrasonography and euthyroid obese people have greater TSH, FT3, and FT3/FT4 ratios than non-obese individuals in a euthyroid condition. Moreover, a reduced expression of the TSH receptor and altered function of deiodinases has been found in the adipose tissue of obese patients. Current data do not support the necessity of a pharmacological correction of the isolated hyperthyrotropinemia in euthyroid obese patients because treatment with thyroid hormone does not significantly improve weight loss and the increase in serum TSH can be reversible after hypocaloric diet or bariatric surgery. On the other hand, obesity is linked to elevated leptin levels. Inflammation can raise the risk of Hashimoto thyroiditis, which increases the likelihood that obese patients will experience overt or subclinical hypothyroidism. Both metabolic syndrome and subclinical hypothyroidism are associated with atherosclerosis, liver and kidney disease. Hence, the association of these two illnesses may potentiate the adverse effects noted in each of them. Subclinical hypothyroidism should be identified in patients with obesity and treated with appropriate doses of L-thyroxine according to the lean body mass and body weight. Randomized controlled trials are necessary to verify whether treatment of thyroid deficiency could counteract the expected risks.