Obesity is characterized by an abnormal or extensive accumulation of adipose tissue. According to the World Health Organization (WHO) categories, obesity is defined as a body mass index (BMI) [weight/height³ (kg/m²)] of ≥30 kg/m² (1). The global incidence rate of overweight and obesity has doubled since 1980, and almost one-third of the world’s population is now classified as overweight or obese (2). Obesity has been a heated topic in research as a risk factor for mortality (3), which can cause a series of adverse events, such as cardiovascular disease (CVD), type 2 diabetes, and cancers (4–9), affecting the lifetime and increasing mortality among older people. In recent years, attention has been paid to sarcopenia and the accompanying decline in muscle mass, strength, and performance. Due to regional and age-related variations, the prevalence of sarcopenia ranges from 1% to 29% in the community living population and from 14% to 33% in the long-term care population (10). In the 1999–2004 National Health and Nutrition Examination Survey (NHANES), the prevalence of sarcopenia was approximately 23%–30% in adults ≥60 years old (11). Appendicular skeletal mass (ASM) is commonly applied to reflect skeletal muscle mass, and in the criteria for commonly used definitions of sarcopenia, the appendicular skeletal mass index (ASMI), which is based on ASM after adjusting height, is most widely used (12). Muscle loss is associated with the incidence of death (13, 14), cardiovascular disease (15), and cancer mortality (16).

Based on the aforementioned characteristics of obesity and sarcopenia, sarcopenic obesity (17) has risen as a new consideration. According to previous studies, the average prevalence of sarcopenic obesity ranges from 5% to 10% in older adults (18). Regarding the correlation between sarcopenia and obesity, we can boldly speculate that patients with obesity tend to have limited mobility, and because the body may be too heavy to exercise effectively, muscle mass declines. In turn, the decline of muscle mass weakens metabolic capacity, and the subsequent intake of calories is easily converted into fat accumulation in the body, forming a vicious cycle. Therefore, sarcopenia and obesity can co-occur and are synergistically associated with greater functional decline and higher mortality than either condition alone (19, 20).

With aging, loss of height and muscle mass and increment of fat mass separate the associations between BMI and obesity and weaken the relationship with mortality (21). Therefore, it is important to choose an appropriate anthropometric measure that reflects body composition to better predict mortality. Body composition refers to the amount and distribution of fat and fat-free tissues in the body (1). However, multiple anthropometric measures do not reflect body composition effectively or are easily affected by other body factors, such as BMI, waist circumference (WC), waist-to-height ratio (WtHR), and waist-to-hip ratio (WHR) (22–26). Recently, the A Body Shape Index (ABSI) has been introduced as a new anthropometric measure (27). ABSI is based on WC adjusted for height and weight, which can better explain the degree of central abdominal adiposity (28, 29). Previous studies have shown that ABSI is more strongly associated with mortality than BMI or WC (6, 29–31). However, the joint effect of higher ABSI values and sarcopenia on mortality is unclear. This study was the first to evaluate whether the joint effect of higher ABSI values and sarcopenia led to a higher risk of total, cardiovascular, and cancer mortality compared with participants with higher ABSI values or sarcopenia. The findings from this study can be helpful in assessing the capacity of considering both fat and muscle mass to screen high-risk populations and provide strategies regarding health management and population-level interventions.

Our main finding is that after adjusting for multiple factors, with increasing ABSI, total and cause-specific mortality of male participants as well as total and cardiovascular mortality of female participants significantly increased. More importantly, when higher ABSI was integrated with sarcopenia, the mortality rates in men were significantly higher than those caused by a single factor (higher ABSI or sarcopenia). However, only all-cause mortality was consistent with this association among women.

Previous studies (4, 32–35) indicated racial differences in the predictive mortality power of ABSI, which was originally formulated based on data from White, Black, and Hispanic individuals (27). Our data suggested that as ABSI increased, the proportion of Black participants gradually decreased from the first to the fourth quartile, which indicated that the body composition of Black participants had a generally lower ABSI. Previous studies have shown that older Black men and women generally possess higher appendicular lean mass and BMI than older White men and women (36–38). Our data also covered the educational background and annual household income of participants; therefore, social and economic factors can also influence the proportion of Black individuals among groups (38), which is worthy of further study.

The impact of ABSI on mortality may be sex-specific in this study, similar to previous reports (35, 39, 40). Specifically, we found that the relationship between ABSI and all-cause and cause-specific mortality was not significant in women. Some speculation and facts could explain why ABSI may not be an appropriate predictor of the risk of death in women. First, the men in our study had higher baseline ABSI levels and a higher prevalence of diabetes mellitus. Second, there was a lower frequency of cardiovascular events in women (Q1, 5.5%; Q2, 7.5%; Q3, 8.1%; Q4, 9.0%) than in men (Q1, 14.3%; Q2, 16.4%; Q3, 17.2%; Q4, 12.8%), and the subsequent statistical power might be lower, which could explain the lack of the associations among women. Third, the span of the ABSI values in female participants was larger than that in male participants, and ABSI was highly clustered around the mean with relatively small variance (41). Therefore, when the span is large and the number of groups is small, some potential connections may be obscured. Finally, the ABSI was originally designed to assess the impact of central obesity (6), since the location of fat accumulation is more important than the actual amount of body fat (14). Due to differences in fat distribution between men and women, more central fat is deposited among men with age (42). This could be one reason why the association between ABSI and mortality was not observed among women.

There are some possible explanations for ABSI’s predictive power for total and cause-specific mortality. First, the distribution of body fat is more predictable than overall obesity in predicting death (43), and ABSI can better reflect central obesity than WC, BMI, or WHR (6). Second, age is a crucial factor in the assessment of the death rate, and aging is frequently accompanied by an increase in visceral fat and a decrease in muscle mass (44). ABSI tends to increase significantly with aging (27). In summary, ABSI better reflects adenoidal obesity and age, and therefore, it better predicts mortality.

In this study, AMSI gradually decreased from the first to the fourth quartile of ABSI, regardless of sex, which indicated that muscle loss tended to accompany the accumulation of adipose tissue. When both coexist, they can synergistically increase the risk of death (19). This is consistent with the results in Table 4. There are several common mechanisms underlying sarcopenia and obesity. First, the increased generation of diverse substances from fat tissue, such as tumor necrosis factor-α (TNF-α) and leptin, can affect insulin resistance and energy metabolism, leading to the loss of muscle mass and the deposition of body fat (45). Second, age was a significant factor. All participants were aged ≥60 years, as significant age-related differences exist in the body compositions of men and women aged ≥60 years, such as loss of muscle mass and an increase in fat mass (46–48). Third, C-reactive protein (CRP) and interleukin-6 (IL-6), which have been demonstrated to be important predictors of muscle loss in people aged ≥55 years old, have been shown to be positively associated with fat mass and negatively associated with muscle mass (49, 50). Muscle loss and fat increase, including but not limited to the above mechanisms, produce a vicious cycle, which further leads to an increased risk of all-cause, cardiovascular, and cancer mortality (6, 51, 52).

The strength of the present study was that the joint association of ABSI and sarcopenia with all-cause and cause-specific mortality was evaluated for the first time, and this joint association may be sex-specific. The outcome of our study is that individuals who suffer from sarcopenia and high ABSI have a significantly higher risk of death than those without sarcopenia or with low ABSI, which stresses the urgency for a scientifically rational assessment of obesity and sarcopenia. ABSI can better assess abdominal obesity, and ASMI can evaluate lean mass. The combination of both can significantly increase the predictive power of mortality, thereby facilitating more targeted interventions to improve quality of life and extend life expectancy among older people. Current evidence suggests that progressive resistance exercise (RE) and aerobic exercise (AE) effectively reduce the risk of obesity and sarcopenia (53–55). Consequently, comprehensive assessment, diagnosis, and treatment of obesity and sarcopenia should be more greatly considered for hospitalized patients to reduce the incidence of adverse events and improve their prognosis.

Our study had some limitations. First, certain essential information regarding preexisting disease interventions, such as antihypertensive drugs, antidiabetic drugs, and CAD treatment, is unavailable and is often associated with study outcomes. Second, the sample size of women was not large enough to ensure that the study results lacked statistical significance. Third, smoking, alcohol consumption, physical activity, and dietary quality were not considered important confounding factors. Fourth, there were no other anthropometric measures of the participants for comparison, such as BMI and WC.

In conclusion, the joint effect of high ABSI and sarcopenia is strongly associated with all-cause and cause-specific mortality, compared with the impact of high ABSI or sarcopenia alone. ABSI and ASMI may be appropriate indices for assessing the proportionate relationship between adiposity with sarcopenia and mortality and should be considered for use in routine clinical care and as intervention indices as a result. However, the use of these indicators to assess female mortality requires further investigation and discussion.

The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding authors.

This article does not contain any studies with human participants or animals performed by any of the authors.

The authors are solely responsible for the design and conduct of this study, all the study analyses, the drafting and editing of the manuscript, and its final contents. J-BZ is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

This work was supported by the National Natural Science Foundation of China (No. 82070851, 81870556), Beijing Municipal Administration of Hospital’s Youth Program (QML20170204), and Excellent Talents in the Dongcheng District of Beijing.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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