The prevalence rate of SCH in our study is 7.6% and higher in women (10.5% vs 6.3%, P < .01), which is compatible with the rate in the Western population (4%-20%)[2,3] and more common in females and aged individuals, but a higher prevalence rate than that in Taiwan (1.6%-4.5%).[4,5] The main differences are the age and sex of the people involved in this study.
The manifestation of hypothyroidism with CVD in VAT is well established, but the effect of SCH is unclear. In the literature, different adipose compartments have different endocrine functions. It has been clearly proved that VAT will also accompany different metabolic risks and morbidities.[31,32] For example, VAT is a more pathogenic fat that is more likely to cause metabolism and CVD risks than subcutaneous adipose tissue.[31,32]
In our study, we found a higher risk of TAT and BRI in an SCH group of Taiwanese women, and an increased impact of CVAI in an SCH with intermediate/high CV risk group. A strong correlation was found between BRI and CVAI in all groups. Region-specific cardiovascular fat tissue (PCF and TAT) is one kind of visceral fat reservoir that is proposed to have a negative effect on blood vessels in a localized manner.[33,34] TAT can envelope the aorta, contributing to CV pathogenesis and potentially explaining the correlation between high TAT and SCH incidence. In a previous study, the Framingham study found that even people with normal VAT had higher cardiometabolic risk if they had high TAT. Our research findings also support the results that, in women with SCH, if the Framingham Research Index was intermediate to high, the TAT was higher than that of the control group (TAT: SCH/EU: 9.17 ± 8.91/6.43 ± 4.30, P = .04), and the risk of TAT was higher (OR = 4.01; 95% CI, 1.01–6.64). We did not find a relationship between PCF and SCH group in this study.
Continuing epidemiological evidence shows that simple and cheap anthropometric methods can be used to predict Mets, such as BRI, ABSI, and VAI, which have historically been used for clinical diagnosis.[17,19,35] BRI is a predictor of body fat and VAT volume and has been postulated to be an indicator of DM and CV health status.[17,36] Some studies in China and Peru have found that BRI is a strong predictive index for the occurrence of Mets in men and women.[37,38] Based on these findings, it has been suggested that BRI could be an effective yet simple clinical screening tool for cardiometabolic risks and Mets.[17,36]
VAI is a useful surrogate index for predicting cardiometabolic disorders in White populations, and the CVAI has a higher overall DM diagnostic ability than BMI, WC, and ABSI in Chinese adults. Krakauer and Krakauer proposed the ABSI in 2012, and it was found to be a better index for measuring metabolic changes and disease risk in the United States than BMI and WC. Some studies have found there is a positive correlation between ABSI and disease risk and mortality hazard.[39,40] However, other studies have obtained opposite results.[36,41]
Our study found that elevated TAT, BRI, and CVAI scores correlate stronger with SCH women compared to men with SCH. Interestingly, these sex-related differences even pertain to intermediate/high CV risk (AR10y by FRS). After multivariable logistic regression analysis, we found that higher risk of TAT and BRI in the SCH group; in addition to BRI and TAT, a higher risk of CVAI was noted in the SCH with intermediate/high FRS risk group, especially in women. The rationale underlying these observations is not clear, but it may be related to sex variations in the distribution of visceral fat deposition and regional adipose tissue. The mechanisms that contribute to the development of SCH from visceral adiposity may be different in men and women. In addition, age and sex are recognized risk factors for thyroid disease, and women in the third TAT, third BRI, and third CVAI tertile were older than men in the SCH group (data not shown), hence SCH risk is influenced by a number of biological factors, including age, sex, and unfavorable health traits. Based on our findings and the available literature, we propose that TAT, BRI, and CVAI serve as markers of SCH risk for women, even in the intermediate/high CV risk group. Visceral fat deposition should be prioritized by women to reduce the occurrence of negative health outcomes.
Key strengths of the study include the fact that, as far as we know, our study is the first to analyze the VAT by using noninvasive, clinically measurable surrogates (BRI, ABSI, and CVAI) or region-specific CV fat tissue quantified using MDCT (PCF and TAT) in identifying body fat distribution in SCH with different CV risk groups. Another advantage was that we analyzed for each sex. A lot of research has discussed fat distribution differences between the sexes. Therefore, our research found that SCH women even in low or intermediate/high CV risk groups had a higher VAT risk than men.
Our study has several limitations. First, the cross-sectional data analyses cannot make causal inferences regarding the relationships between TAT, BRI, and CVAI and SCH risks. Second, after stratification, the number of participants in each group was small, which would affect the effectiveness of statistics. In the future, a larger sample size and cohort study may be needed for causality analysis.
J Endo Soc. 2021;5(6) © 2021 Endocrine Society