Skeletal muscle mass to visceral fat area ratio is associated with metabolic syndrome and arterial stiffness: The Korean Sarcopenic Obesity Study (KSOS)
Introduction
Aging is frequently associated with a decrease in muscle mass and/or strength, also known as sarcopenia, and a relative increase in visceral fat [1], [2]. The imbalance between skeletal muscle mass and visceral fat mass in older individuals occurs even in the absence of significant changes in body mass index (BMI) and may have synergistic effects on health outcomes including metabolic disorders, cardiovascular disease (CVD) and mortality [2], [3]. These imbalances are extreme in some individuals, producing a condition that is a combination of obesity and sarcopenia, a condition recently termed “sarcopenic obesity”. However, several previous epidemiologic studies failed to find the association between sarcopenic obesity and cardiovascular risk factors [4], [5]. In the New Mexico Aging Process Study, the prevalence of metabolic syndrome was highest in the non-sarcopenic obese group, followed by the sarcopenic obesity group, and normal group, and was lowest in the sarcopenic non-obese group [4]. Similarly, in obese postmenopausal women, sarcopenia appeared to be associated with lower CVD predisposing risk factors [5]. In the EPIDOS study, sarcopenia was not associated with physical difficulties in the absence of obesity. However, in the presence of obesity, sarcopenia tended to add difficulties in physical function [6]. Because skeletal muscle mass and total body fat are closely correlated, an increase in skeletal muscle mass is often accompanied by gain in total body fat [7]. Therefore, assessment of the effect of sarcopenia on metabolic syndrome and atherosclerosis might require simultaneous consideration of visceral obesity.
Appendicular skeletal muscle mass (ASM) is an important index of sarcopenia that can be measured by dual energy X-ray absorptiometry (DXA), a noninvasive, highly reproducible and accurate technique [8], [9], [10]. Visceral fat area (VFA) can be measured by computed tomography (CT) which is considered the gold standard method for determining visceral adiposity [11]. Although sarcopenia and visceral obesity may potentiate each other, resulting in a substantial effect on metabolic disorders and atherosclerosis in older persons, most studies thus far have investigated the role of sarcopenia and visceral obesity separately. Therefore, we present and evaluate a new surrogate index of sarcopenic obesity using the ratio of ASM-to-VFA that we call muscle-to-fat ratio (MFR).
Arterial stiffness measured as pulse wave velocity (PWV) is also known to increase with aging. PWV is an indicator of atherosclerosis and an independent predictor of cardiovascular risk in the general population [12], [13]. Brachial-ankle PWV (baPWV) can be used as a simple and reliable marker to screen the general population for the presence of CVD [14], [15]. Several proposed underlying mechanisms of sarcopenic obesity, including aging, sedentary life style, inflammation and insulin resistance, are also known to be related to atherosclerosis [3]. Recently, Ochi et al. reported that arterial stiffness is negatively related to thigh muscle volume in men but not in women [16]. However, they did not consider visceral fat in their analysis and used thigh muscle cross-sectional area as an indicator of sarcopenia.
Based upon these findings, we hypothesize that sarcopenia and obesity interact with each other to further facilitate atherosclerosis. However, there are no studies evaluating the association between surrogate index of sarcopenic obesity and atherosclerosis, indicating that a decrease in MFR is going to be related to higher baPWV.
Herein, in order to prove our hypothesis we evaluated the possible relationship between MFR, an index of skeletal muscle mass corrected by visceral obesity, and components of metabolic syndrome. We further examined the association between MFR and arterial stiffness in an apparently healthy general population.
Section snippets
Study subjects
We analyzed baseline cross-sectional data from the Korean Sarcopenic Obesity Study (KSOS), an ongoing epidemiologic study supported by Korea Science and Engineering Foundation. This prospective observational cohort study was designed to examine the prevalence of sarcopenia and sarcopenic obesity in Korean adults with (diabetic KSOS cohort) or without diabetes (non-diabetic KSOS cohort) and to evaluate their effects on metabolic disorders and health outcomes [17], [18]. In this study, eligible
Results
The age of enrolled subjects ranged from 20 to 80 years with a mean of 53.6 ± 15.6 years, and 68% were female. Anthropometric indicators such as BMI, ASM, ASM/height2, mid-thigh muscle area, and VFA, SBP, DBP, triglyceride, FPG, and baPWV were all higher in men than in women (Table 1). By contrast, SFA, total body fat percentage and HDL-cholesterol were significantly higher in women. Interestingly, there was no significant difference of MFR as well as age and LDL-cholesterol between men and
Discussion
In this study, we found that MFR was significantly decreased in subjects with metabolic syndrome and associated with all the components of metabolic syndrome. Decreased MFR was a dependent risk factor for metabolic syndrome after correction for other confounding parameters. Furthermore, MFR was independently and negatively associated with arterial stiffness even after adjusting for other risk factors.
Changes in body composition during aging are associated with important effects on health and
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
This study was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea Government (R01-2007-000-20546-0) and a grant from the Korean Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (A 050463).
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