Abstract and Introduction
Context: From previous studies, decreased thermogenesis and metabolic rate in the patients with overt and subclinical hypothyroidism lead to an increase in visceral adipose tissue (VAT) incidence, and which was associated with cardiovascular diseases. In this paper, we want to explore the relationship between various forms of VAT [pericardial (PCF), and thoracic periaortic adipose tissue (TAT)] and obesity indices [body shape index (ABSI), and body roundness index (BRI), Chinese visceral adiposity index (CVAI)] with subclinical hypothyroidism by gender.
Objective: This study aims to evaluate region-specific cardiovascular (CV) fat tissue (pericardial fat [PCF] and thoracic periaortic fat [TAT) and noninvasive visceral adipose indices (a body shape index [ABSI], body roundness index [BRI]), and Chinese visceral adiposity index [CVAI]) in patients with subclinical hypothyroidism (SCH) as compared to a control population and relative to variations in CV risk.
Methods: A total of 125 Taiwanese patients recently diagnosed with SCH (age: 52.9 ± 10.16 years, 41.6% female) and 1519 healthy volunteers (age: 49.54 ± 9.77 years, 29.0% female) were evaluated for this study. All participants underwent PCF and TAT assessment using a multidetector computed tomography scanner, ABSI, BRI, and CVAI evaluation using a mathematical formula. CV risk was classified by Framingham risk score (FRS).
Results: Multivariable logistic regression models showed that the independent association of TAT and BRI with SCH were stronger in women than men. The adjusted model associations (odds ratio [OR]; 95% CI) with SCH for TAT and BRI in women were 2.61 (95% CI, 1.03–6.97) and 2.04 (95% CI, 1.07–3.92). The incidences of TAT and BRI third tertile were also higher in women with SCH (SCH vs euthyroid, TAT third tertile, 9 [17.3%] vs 35 [7.9%], P = .04; BRI third tertile, 22 [42.3%] vs 111 [25.2%], P = .01). In addition to BRI and TAT, there were higher risks of CVAI in SCH with intermediate/high FRS, especially in women (OR; 95% CI, TAT: 4.01; 95% CI, 1.01–6.640; BRI: 6.91; 95% CI, 1.03–10.23; CVAI: 7.81 95% CI, 1.01–12.03).
Conclusion: Our findings show that patients with SCH have significantly greater TAT, BRI, and CVAI values than control groups, especially in women (with different FRS).
Subclinical hypothyroidism (SCH) is a disease characterized by the lack of obvious clinical symptoms and signs; laboratory tests are defined as elevated levels of thyrotropin (TSH) despite the concentration of the serum thyroid hormone falling within the expected, normal range. The prevalence of SCH is about 4% to 20% in the Western population,[2,3] with a higher incidence in aging women. In Taiwan, the prevalence of subclinical hypothyroidism reported in the past was about 1.6%, but in recent reports, the prevalence rate reached 4.5%.
Decreased thermogenesis and metabolic rate in the patients with overt and subclinical hypothyroidism lead to an increase in visceral adipose tissue (VAT) incidence. There is a substantial body of evidence that confirms VAT's association with systemic inflammation, metabolic syndrome (Mets), diabetes mellitus (DM), and cardiovascular disease (CVD).[7,8] Various forms of VAT are implicated in disease pathology, including visceral abdominal, pericardial fat (PCF), and thoracic periaortic adipose tissue (TAT).
PCF and TAT are subtypes of perivascular fat that have been identified as novel risk markers for CVD.[9,10] A previous study found significantly higher TAT values in SCH patients than control groups as well as a significant correlation with TSH levels, but no differences with respect to sex. A relationship between PCF and SCH has not been established; the majority of research has reported that increased epicardial adipose tissue (EAT) may contribute to cardiovascular (CV) adverse effects associated with SCH.[12,13] Despite this, a recent study by Santos et al concluded that EAT is not a strong marker of CVD for SCH patients. In fact, PCF must be anatomically and biochemically distinguished from EAT.
The body roundness index (BRI), a body shape index (ABSI), and the Chinese visceral adiposity index (CVAI) depict fat distribution and are reliable biomarkers of body fat accumulation in a Chinese and Iranian study.[15,16] BRI (based on waist circumference [WC] and height) was proposed by Thomas et al in 2013 and was demonstrated to be a novel anthropometric index better at detecting cardiometabolic abnormalities among Chinese women than body mass index (BMI) and waist-to-height ratio. ABSI (based on height, weight, and BMI) has also been shown to be superior to BMI in predicting premature mortality and is the best anthropometric index available for predicting the incidence of CVD among men. Another indicator of Chinese visceral fat is the CVAI (based on WC and BMI; triglycerides [TGs], and high-density lipoprotein cholesterol [HDL-C]), which measures visceral adiposity among the Chinese general population, with separate formulas for men and women. Studies have positively supported CVAI's ability to predict Mets and CVD in this population.[21,22]
There are inconclusive opinions regarding SCH's ability to accurately determine CVD risk. Increasing evidence suggests that an association exists between atherosclerotic CVD and SCH;[23,24] one meta-analysis study reported that SCH patients have an increased risk of CVD, and a similar population-based study noted SCH is an independent predictor for CVD. Despite this, a 20-year cohort investigation did not establish a significant association between SCH and CVD.
Sex-linked variations have been demonstrated in visceral fat deposition patterns and regional fat tissue distribution. The mechanisms that underlie the progression of SCH to visceral adiposity may differ based on sex, although additional research is required. While SCH has been established as a predisposing factor for increased CV risk, there is less literature available about the effect of visceral adipose indices (BRI, ABSI, CVAI, PCF, TAT) in SCH patients by sex.
We hypothesize that body fat distribution in SCH or euthyroid (EU) groups could be identified using noninvasive, clinically measurable surrogates (BRI, ABSI, and CVAI) or region-specific CV fat tissue quantification via multidetector computed tomography (MDCT; PCF and TAT). We aim to assess the correlation between obesity indices and SCH risk by sex in different FRS risk group.
J Endo Soc. 2021;5(6) © 2021 Endocrine Society