It is well known that abdominal fat is a causal factor of cardiometabolic diseases, whereas muscle mass plays a protective role in those diseases (1
). Muscle mass is gradually decreased with age, even if body weight or body fat mass is unchanged or slightly increased. That phenomenon, so-called sarcopenia or sarcopenic obesity, is frequently observed in the elderly as well as young or middle-aged adults with chronic disease. Subjects with a particular phenotype may be more prone to developing metabolic and cardiovascular diseases than those with the opposite phenotype or those with high abdominal fat mass alone (15
). Therefore, both body fat (especially abdominal) and muscle mass need to be considered when assessing the risk for those diseases. The current study compared WC, CC, and WCR to carotid atherosclerotic burden. We demonstrated that CC was negatively and WC was positively associated with carotid atherosclerotic burden. Furthermore, the WCR had the strongest association with carotid atherosclerosis compared with each circumference, and that association was independent of multiple potential confounders.
Computed tomography and magnetic resonance imaging have been considered to be the gold standards for assessing visceral fat and skeletal muscle distributions. Previous studies reported that the ratio of visceral fat to thigh muscle area is a good parameter that reflects insulin resistance and is an indicator for the risk of metabolic syndrome (17
). However, the clinical application of those imaging devices is limited because of the time required, cost, accessibility, and risk of radiation exposure. The simplest and most widely used method for assessing visceral fat accumulation and assuming the disproportion between abdominal fat and lean mass is measuring WC and WHR, which are well known as anthropometric parameters to reflect cardiovascular risks (1
). However, recent studies demonstrate that measuring WC alone may be insufficient to assess the visceral fat amount or predict the cardiometabolic risk (21
). Indeed, even subjects with a normal WC are more prone to having carotid atherosclerosis if they have centrally located body fat (22
). Also, in the case of WHR, there are a number of problems inherent in the use of a ratio indicator. Because of the equation used to determine that value, both lean and massively obese individuals may end up having the same WHR.
WTR has been proposed as an new alternative index for abdominal obesity and is more strongly associated with cardiovascular and metabolic risk factors than WHR (11
). However, thigh circumference, a component of WTR, may also be as confounded anatomically as hip circumference. Two different anatomical landmarks have been used to determine the exact location for measuring thigh circumference, directly below the gluteal fold and at the midthigh (4
). Wherever measured, there are substantial errors in every measurement. Moreover, thigh circumference is not convenient to measure in practice because of disrobing and, in particular, measurement of proximal thigh circumference may be uncomfortable for some individuals. In contrast, the measure of CC has several advantages over thigh circumference. It requires only rolling the pants up to the knees. It is more culturally acceptable in many cases and less susceptible to measurement and calculation errors than a measure of thigh circumference. Also, CC is a potential marker of leg muscle mass (24
). For this reason, we selected CC as an anthropometric index representing leg lean mass and WCR as an index for assessing the disproportion between abdominal fat and leg muscle mass. Of course, WCR might also be susceptible to measurement and calculation errors by requiring the ratio of two measures as opposed to a single measurement. However, simultaneously measuring both WC and CC could provide more specific information for sarcopenic phenotype compared with either a WC or CC measurement. In our study, WCR had a better correlation with CIMT than WC or CC (r
= 0.242, P
< 0.001 vs. r
= 0.079, P
< 0.001 or r
= −0.143, P
< 0.001 in men; r
= 0.255, P
< 0.001 vs. r
= 0.144, P
< 0.001 or r
= −0.111, P
< 0.001 in women, respectively).
Our analysis demonstrated an opposite and multiplicative relationship of WC and CC with the frequency of carotid atherosclerosis in both sexes, the highest frequency being found in subjects with the highest quartile of WC and the lowest quartile of CC. The independent association with carotid atherosclerosis across quartiles of each index was observed only in the WCR in both sexes and in CC in men. The CIMT was larger with increasing WCR and WC and decreasing CC in both sexes, but except for WCR in women, the association disappeared after adjusting for multiple confounders. The associations with CIMT and atherosclerosis across WHR quartiles were not observed in both sexes, and in the case of WTR, the odds of carotid atherosclerosis across WTR quartiles were lower than WCR quartiles (data not shown). This indicates that WCR may be a better indicator for carotid atherosclerotic burden than other anthropometric indices.
Several limitations of this study should be noted. First, the cross-sectional study design limited conclusions regarding the direction or causality between the anthropometric indices and cardiometabolic risk. Second, our study showed an independent association of WCR with carotid atherosclerosis but did not observe the cardiovascular events and mortality. Also, we could not investigate a degree of physical activity, which could largely affect leg lean mass. Third, the contribution of fat or lean mass distribution to metabolic and cardiovascular diseases may vary among different populations. Accordingly, our results may differ from those in other ethnic groups. Fourth, we did not suggest a definite cutoff value of WCR or CC to screen subjects at higher risk for carotid atherosclerosis. Finally, CC is a surrogate marker of lean mass or peripheral subcutaneous fat. We cannot understand whether the inverse association between carotid atherosclerosis and increasing CC or decreasing WCR is due to a protective effect of either a large amount of lean mass or peripheral subcutaneous fat or both. Thus, it may warrant further investigation using a longitudinal study design and implementing computed tomography or magnetic resonance imaging to measure the muscle and fat distribution within the calf separately.
This study also has several strengths. This study was performed using a relatively large cohort of type 2 diabetes performed in one institute. In particular, carotid Doppler was performed, and all data collection procedures including anthropometric indices were obtained by one trained study staff. This is the first study investigating the association of WCR, a relatively new measure of abdominal adiposity, and carotid atherosclerosis. It also adds to the growing discussion with regards to the characterization of high-risk phenotypes and the value of anthropometric measurements for clinical risk stratification.
The results of our study suggest that WCR may be superior to each single measure of WC or CC in association with prevalent carotid atherosclerosis. It is speculated that putting on abdominal fat and losing leg muscle might act synergistically, causing carotid atherosclerosis. WCR may be a useful and practical anthropometric index that facilitates the early identification of diabetic subjects with high risk for cardiovascular disease.