Prevalence of sarcopenia and sarcopenic obesity in Korean adults: the Korean sarcopenic obesity study

Abstract

The epidemiological trends that characterize our generation are an obesity epidemic and the aging of the population.1 Aging results in a progressive loss of muscle mass and strength called sarcopenia, which is Greek for ‘poverty of flesh’.2 Sarcopenia leads to functional impairment and physical disability.3 Moreover, aging and physical disability are also related to an increase in fat mass, particularly visceral fat,4 which is an important factor in the development of metabolic syndrome and cardiovascular disease.5 Therefore, sarcopenia and obesity in the elderly may synergistically increase their effect on physical disability, metabolic disorders, cardiovascular disease, and mortality.6 A combination of excess body fat and reduced muscle mass and/or strength with aging is defined as sarcopenic obesity (SO). Surplus energy intake, physical inactivity, low-grade inflammation, and changes in hormones, such as growth hormone and testosterone, may all be related to the development of SO.6 As the obese elderly population is continuously increasing, the impact of SO is estimated to be dramatic in the next decade.2 Korea is rapidly aging. According to the Korea National Statistical Office, 7.2% of the Korean population was aged 65 and older (i.e. elderly) in 2000. The percentage is expected to rise to 19.1% in 2025 and 34.4% in 2050.7 The speed at which Korea is becoming an aged society is unprecedented among developed countries. Research regarding the impact of SO is essential for the development of public health programs for the increasingly elderly Korean population. Several definitions of sarcopenia and SO have already been proposed in western countries. Baumgartner et al. defined sarcopenia as reduction in appendicular skeletal muscle mass (ASM) divided by height squared (ASM/height2) of two s.d. or more below the normal means for a younger reference group measured using dual X-ray absorptiometry. They defined SO as ASM/height2 of two s.d. below the value of a young reference group and median of total body fat percentage and reported that the prevalence of SO was 4.4% in men and 3.0% in women over 60 years of age in the New Mexico Aging Process Study (NMAPS).6, 8 In community-dwelling elderly women in Verona, Italy, Zoico et al.,9 defining SO as the two lower quintiles of ASM/height2 plus two higher quintiles of fat mass, reported that the prevalence of SO was 12.4%. Using the same definition, Davison et al.10 reported that the prevalence of SO was 9.6% in men and 7.4% in women from the bioelectrical impedance analysis data of NHANES III. The ASM/height2 index is highly correlated with body mass index (BMI) as a current criterion for obesity.11 Thus, this index primarily identified thin people as sarcopenic and could have limited applications for underestimating sarcopenia in overweight or obese subjects.12 To overcome this limitation, Newman et al.11 and Delmonico et al.12 proposed new criteria for sarcopenia based on the amount of lean mass being lower than expected for a given amount of fat mass using residuals from linear regression models. In addition, Janssen et al.3 proposed a definition of sarcopenia as skeletal muscle mass index (SMI (%), skeletal muscle mass (kg)/weight (kg) × 100) of one or two s.d. below the mean for a younger reference group. However, Newman et al. or Janssen et al. did not specifically define SO and they only defined sarcopenia. The prevalence of sarcopenia and SO may vary depending on the criteria, reference populations, and definition used. Although many obese persons with low muscle mass in relation to body weight have disabilities and cardiometabolic risk factors,11, 13 the ASM/height2 index does not identify most obese people with sarcopenia. For this reason, we present a new definition of SO using the SMI of two s.d. below the value of a young reference group (Janssen's definition of sarcopenia) and the upper two quintiles of the total body fat percentage (Zoico's definition of obesity). Despite the growing importance of SO, only a few studies evaluating the definition and prevalence of SO was performed in Caucasian populations and there have been no earlier studies in non-Caucasian populations. Furthermore, there are very few reports about a relationship between SO and metabolic disorders. We examined the prevalence of sarcopenia and SO using different definitions in Korean adults. In addition, we evaluated the associations of SO and metabolic parameters and explored the relationship between SO and metabolic syndrome. Obesity was defined as values greater than the median total fat percentage for each sex 8 or the upper two quintiles for total body fat percentage of the study population.9, 10 SO was defined as high total body fat percentage and low relative skeletal muscle mass in the same subjects according to other earlier studies.8, 9, 10 We classified four sarcopenia/obesity groups by using the new criterion of SMI of two s.d. below the value of a young reference group and the upper two quintiles for total body fat percentage. The four groups included the following: normal body fat and muscle mass, sarcopenia (and normal body fat), obesity (and normal muscle mass), and SO. The cutoff values for obesity, defined as the two highest quintiles of total body fat percentage, were 20.21% for men and 31.71% for women, respectively. This study estimated the prevalence of sarcopenia and SO in Korean men and women using different criteria including our new method. We examined cutoff points to define sarcopenia and SO in the Korean population, which turned out to be different from those used to evaluate Caucasian population. Different definitions of sarcopenia and SO yield varying prevalence values. We found that the lowest SMI quintile is associated with a greater likelihood of metabolic syndrome in Korean population. Among the different indices of sarcopenia and SO used in our study, SO only defined using the new method was associated...