Background
Life expectancies are increasing in most ethnic groups and countries, as are the survivals of older people with impaired physical functions and disabilities [
1,
2]. Accordingly, there is a great deal of research interest in precursors, including sarcopenia, in older people with impaired physical functions and disabilities [
3,
4].
Sarcopenia is a term applied by Irwin Rosenberg in 1989 to explain age-associated loss of muscle mass and muscle function [
5]. Thereafter, researchers have added impaired functional performance and/or muscle weakness of clinical importance to the loss of muscle mass incorporated in the concept of sarcopenia. The Foundation for the National Institute of Health (FNIH) Sarcopenia Project defined sarcopenia as clinically relevant low muscle strength (weakness) and low lean mass in 2014 [
6]. The Asian Working Group for Sarcopenia (AWGS) guideline also addressed cut-off points for Asian older people by modifying the European Working Group on Sarcopenia in Older People (EWGSOP) guideline [
7].
The EWGSOP, International Working Group in Sarcopenia (IWGS) and AWGS guidelines define the sum of the muscle masses of the four limbs as appendicular skeletal mass (ASM) to calculate appendicular skeletal mass index (ASMI) as ASM/height
2 (ASM/m
2) [
3,
4,
8‐
10]. However, many other cutoff points have been proposed [
11]. Previous studies among Asian older people showed substantially different cutoff points for low ASMI. Furthermore, the prevalences of low ASMI among Asian women were extremely low, which caused problems for researchers conducting studies on sarcopenia.
This study was conducted to determine the prevalence of low ASMI in accordance with three cutoff points in aged Korean (>65 years), and to explore the relationship between low ASMI and subjective health-related quality of life.
Results
Mean and SD of ASMI in the young men group assuming a normal distribution was 7.81 ± 0.91 kg/m
2 and in the young women group was 5.67 ± 0.78 kg/m
2. If ASMI in the young reference group had a normal distribution, the values of mean-2SD and the lowest 2.28% would have been the same. However, young men group (Kolmogorov-Smirnov p = 0.020) and the young women group (Kolmogorov-Smirnov p < 0.001) did not show a normal distribution due to high kurtosis. In the young men group, the mean-2SD value was 5.99 kg/m
2 and the lowest 2.28% value was 6.09 kg/m
2, and in the young women group corresponding values were 4.12 kg/m
2 and 4.38 kg/m
2, respectively. The difference between the two values was higher in the young women group (0.26 kg/m
2 vs. 0.10 kg/m
2). The ASMI cutoff points in older men were ASMI 2SD (6.09 kg/m
2), ASMI 20 (6.48 kg/m
2), and ASMI 1SD (6.95 kg/m
2), and corresponding values for older women were ASMI 2SD (4.38 kg/m
2), ASMI 1SD (4.96 kg/m
2), and ASMI 20 (5.33 kg/m
2) (Table
1). Characteristics of the older study participants are summarized in Table
2. The proportions in low group for each cutoff point for older men study subjects were 9.7% (ASMI 2SD) and 40.9% (ASMI 1SD), respectively, and for older women were 0.7% (ASMI 2SD) and 7.4% (ASMI 1SD), respectively (Table
3). By univariate analysis with ordinal regression analysis using the complex sample procedure, low ASMI had significantly associated with poorer outcome of five domains of EQ-5D and of the EQ-5D index in older men. More specifically, ASMI ranging from ASMI 2SD to ASMI 20 had higher cumulative odds ratios (ORs) than those with those a normal ASMI [mobility 2.28 (95% Confidence Interval (CI): 1.55-3.35), self-care (OR 2.10, CI: 1.10-4.00), usual activities (OR 2.40, CI: 1.53-3.77), pain/discomfort (OR 1.63, CI:1.13-2.36), anxiety/depression (OR 1.76, CI:1.01-3.09), and EQ-5D index (OR 2.09, CI: 1.45-3.02)] in older men (Table
4). Low ASMI had significantly associated with poorer outcome of domains of self-care and anxiety/depression among the five domains of EQ-5D in older women. More specifically, ASMIs ranging from ASMI 2SD to ASMI 20 had a higher OR for difficulty in self care (OR 1.20, CI: 0.82-1.74) and prevalence of anxiety/depression (OR 0.78, CI: 0.54-1.12) in older women (Table
5).
Table 2
General characteristics of older study participants by gender
Sample size (no.) | 1872 | 2541 |
Weighted size (no.) | 2152083 | 3126111 |
Education | | |
| None | 4.0 (0.6) | 17.6 (1.2) |
| Elementary school | 24.1 (1.4) | 45.3 (1.3) |
| Middle school | 29.1 (1.4) | 26.7 (1.2) |
| High school | 20.3 (1.2) | 6.6 (0.6) |
| Over college grade | 22.5 (1.4) | 3.8 (0.5) |
Family income | | |
| 1st quartile | 53.9 (1.2) | 56.8 (1.4) |
| 2nd quartile | 23.1 (0.8) | 20.5 (1.0) |
| 3rd quartile | 13.0 (0.8) | 12.7 (0.9) |
| 4th quartile | 9.9 (0.8) | 10.0 (0.9) |
BMI (kg/m2) | | |
| Underweight (<18.5) | 6.1 (0.7) | 3.9 (0.5) |
| Normal weight (18.5-22.9) | 43.5 (1.5) | 33.8 (1.2) |
| Overweight (23.0-27.4) | 42.8 (1.4) | 47.6 (1.3) |
| Obese (>27.5) | 7.5 (0.8) | 14.7 (0.8) |
Smoking | | |
| Never Smoking (<100 cigarettes in life) | 17.9 (1.0) | 85.8 (0.9) |
| Passive smoking (>1 hour/day) | 0.6 (0.2) | 2.8 (0.4) |
| Former smoker | 27.8 (1.4) | 2.4 (0.5) |
| Current Smoker | 53.7 (1.5) | 9.0 (0.7) |
Audit-K | | |
| Normal | 70.5 (1.5) | 92.8 (0.8) |
| harmful alcohol consumption | 22.4 (1.2) | 4.6 (0.7) |
| suggestive of alcohol dependence | 7.1 (0.9) | 2.6 (0.5) |
Chronic illness | | |
| Cancer | 6.4 (0.7) | 5.8 (0.6) |
| Diabetes | 16.3 (0.9) | 18.1 (1.0) |
| Hypertension | 41.4 (1.4) | 54.4 (1.3) |
| Stroke | 7.3 (0.7) | 4.2 (0.4) |
| Coronary artery disease | 6.3 (0.6) | 5.2 (0.5) |
| Arthritis | 13.9 (1.0) | 44.9 (1.2) |
| Chronic Pulmonary Disease | 6.0 (0.6) | 6.7 (0.6) |
| Depression | 2.3 (0.4) | 6.2 (0.6) |
| Chronic renal failure | 0.6 (0.2) | 0.6 (0.1) |
| Chronic hepatitis/Liver cirrhosis | 2.5 (0.4) | 1.2 (0.3) |
No. of chronic illness | 1.03 (0.98-1.09) | 1.47 (1.42-1.53) |
Table 3
Prevalence of low ASMI and EQ-5D for older study participants by gender
Sample size (no.) | 1872 | 2541 |
Weighted size (no.) | 2152083 | 3126111 |
ASMI | | |
| ASMI 2SD | 9.7 (0.9) | 0.7 (0.2) |
| ASMI 1SD | 40.9 (1.5) | 7.4 (0.7) |
| ASMI 20 | 20.0 (1.2) | 20.0 (1.1) |
EQ5D | | |
| Mobility |
| | No problem | 65.4 (1.4) | 42.8 (1.3) |
| | Some problems | 32.9 (1.3) | 53.4 (1.3) |
| | Extreme problems | 1.7 (0.4) | 3.8 (0.5) |
| Self-Care |
| | No problem | 90.4 (0.9) | 80.9 (1.0) |
| | Some problems | 8.6 (0.8) | 17.4 (1.0) |
| | Extreme problems | 1.0 (0.2) | 1.7 (0.3) |
| Usual Activities (e.g., work, study, housework, family or leisure activity) |
| | No problem | 76.6 (1.3) | 61.9 (1.2) |
| | Some problems | 19.9 (1.2) | 31.5 (1.1) |
| | Extreme problems | 3.5 (0.5) | 6.6 (0.7) |
| Pain/Discomfort |
| | No problem | 67.3 (1.3) | 47.3 (1.3) |
| | Some problems | 26.9 (1.2) | 38.2 (1.2) |
| | Extreme problems | 5.8 (0.6) | 14.5 (0.8) |
| Anxiety/Depression |
| | No problem | 88.9 (0.9) | 79.5 (1.0) |
| | Some problems | 9.3 (0.7) | 17.4 (0.9) |
| | Extreme problems | 1.9 (0.5) | 3.2 (0.4) |
| EQ5D index |
| | 1 | 52.6 (1.4) | 28.9 (1.1) |
| | 0.775-0.999 | 26.8 (1.3) | 33.5 (1.3) |
| | <0.774 | 20.6 (1.2) | 37.7 (1.3) |
Table 4
Univariate analysis of five domains of EQ-5D and EQ5D index according to ASMI in older men
Mobility | | | | | <0.001* |
| ASMI 2SD | 0.818 | 0.192 | 2.267 | 1.554-3.308 | <0.001 |
| ASMI 20 | 0.824 | 0.195 | 2.280 | 1.554-3.346 | <0.001 |
| ASMI 1SD | 0.311 | 0.159 | 1.365 | 0.998-1.867 | 0.051 |
| Normal | Reference |
Self-care | | | | | <0.001* |
| ASMI 2SD | 1.152 | 0.250 | 3.165 | 1.938-5.169 | <0.001 |
| ASMI 20 | 0.743 | 0.328 | 2.103 | 1.104-4.007 | 0.024 |
| ASMI 1SD | 0.252 | 0.294 | 1.286 | 0.721-2.294 | 0.393 |
| Normal | Reference |
Usual activities | | | | <0.001* |
| ASMI 2SD | 1.153 | 0.195 | 3.169 | 2.159-4.651 | <0.001 |
| ASMI 20 | 0.875 | 0.230 | 2.398 | 1.526-3.767 | <0.001 |
| ASMI 1SD | 0.500 | 0.181 | 1.648 | 1.156-2.350 | <0.001 |
| Normal | Reference |
Pain/discomfort | | | | | 0.010* |
| ASMI 2SD | 0.576 | 0.196 | 1.778 | 1.209-2.615 | 0.004 |
| ASMI 20 | 0.490 | 0.188 | 1.632 | 1.128-2.362 | 0.009 |
| ASMI 1SD | 0.192 | 0.148 | 1.212 | 0.906-1.621 | 0.194 |
| Normal | Reference |
Anxiety/depression | | | | 0.012* |
| ASMI 2SD | 0.788 | 0.272 | 2.199 | 1.289-3.752 | 0.004 |
| ASMI 20 | 0.567 | 0.286 | 1.763 | 1.006-3.090 | 0.048 |
| ASMI 1SD | 0.338 | 0.227 | 1.402 | 0.899-2.188 | 0.136 |
| Normal | Reference |
EQ5D index | | | | | <0.001* |
| ASMI 2SD | 0.879 | 0.161 | 2.408 | 1.755-3.304 | <0.001 |
| ASMI 20 | 0.736 | 0.187 | 2.088 | 1.445-3.016 | <0.001 |
| ASMI 1SD | 0.305 | 0.142 | 1.357 | 1.028-1.792 | 0.031 |
| Normal | reference |
Table 5
Univariate analysis of five domains of EQ-5D and EQ5D index according to ASMI in older women
Mobility | | | | | 0.264* |
| ASMI 2SD | 0.046 | 0.585 | 1.047 | 0.332-3.303 | 0.937 |
| ASMI 1SD | -0.102 | 0.227 | 0.903 | 0.579-1.410 | 0.654 |
| ASMI 20 | -0.242 | 0.146 | 0.785 | 0.589-1.045 | 0.097 |
| Normal | Reference | | | | |
Self-care | | | | | 0.011* |
| ASMI 2SD | 1.634 | 0.561 | 5.122 | 1.702-15.418 | 0.004 |
| ASMI 1SD | 0.412 | 0.252 | 1.510 | 0.921-2.477 | 0.102 |
| ASMI 20 | 0.179 | 0.190 | 1.196 | 0.824-1.737 | 0.345 |
| Normal | Reference | | | | |
Usual activities | | | | 0.087* |
| ASMI 2SD | 1.238 | 0.569 | 3.450 | 1.129-10.542 | 0.030 |
| ASMI 1SD | 0.188 | 0.220 | 1.206 | 0.784-1.857 | 0.394 |
| ASMI 20 | 0.231 | 0.157 | 1.260 | 0.924-1.716 | 0.143 |
| Normal | Reference | | | | |
Pain/discomfort | | | | | 0.522* |
| ASMI 2SD | 1.101 | 0.894 | 3.009 | 0.520-17.416 | 0.218 |
| ASMI 1SD | 0.057 | 0.191 | 1.058 | 0.728-1.539 | 0.767 |
| ASMI 20 | -0.080 | 0.144 | 0.923 | 0.695-1.225 | 0.578 |
| Normal | Reference | | | | |
Anxiety/depression | | | | 0.021* |
| ASMI 2SD | 1.498 | 0.555 | 4.471 | 1.504-13.290 | 0.007 |
| ASMI 1SD | 0.441 | 0.261 | 1.554 | 0.931-2.596 | 0.092 |
| ASMI 20 | -0.253 | 0.188 | 0.776 | 0.536-1.123 | 0.179 |
| Normal | Reference | | | | |
EQ5D index | | | | | 0.858* |
| ASMI 2SD | 0.637 | 0.898 | 1.890 | 0.324-11.034 | 0.479 |
| ASMI 1SD | 0.087 | 0.211 | 1.091 | 0.721-1.650 | 0.681 |
| ASMI 20 | -0.006 | 0.152 | 0.994 | 0.738-1.340 | 0.969 |
| Normal | Reference | | | | |
By multivariate ordinal logistic regression, low ASMI had significantly higher ORs for the three domains of mobility, self-care, and usual activities among the five domains of EQ-5D in older men (Table
4). In detail, the findings with ASMI 20 were mobility (OR 2.54, CI: 1.63-3.95), usual activities (OR 2.31, CI: 1.31-4.09), and EQ-5D index (OR 1.86, CI: 1.23-2.82) in older men (Table
6). However these correlations were not significant for all three cutoff points ASMI 2SD, ASMI 1SD (except ASMI 2SD), and ASMI 20 (except ASMI 1SD) in older women (Table
7).
Table 6
Multivariate analysis of five domains of EQ-5D and EQ5D index according to ASMI in older men
Mobility | | | | | <0.001* |
| ASMI 2SD | 0.698 | 0.272 | 2.010 | 1.117-3.431 | 0.011 |
| ASMI 20 | 0.932 | 0.225 | 2.538 | 1.632-3.948 | <0.001 |
| ASMI 1SD | 0.348 | 0.196 | 1.416 | 0.964-2.079 | 0.076 |
| Normal | Reference |
Self-care | | | | | 0.005* |
| ASMI 2SD | 1.088 | 0.343 | 2.967 | 1.512-5.822 | 0.002 |
| ASMI 20 | 0.637 | 0.397 | 1.890 | 0.867-4.121 | 0.109 |
| ASMI 1SD | 0.270 | 0.313 | 1.310 | 0.709-2.420 | 0.389 |
| Normal | Reference |
Usual activities | | | | 0.004* |
| ASMI 2SD | 1.082 | 0.335 | 2.950 | 1.526-5.701 | 0.001 |
| ASMI 20 | 0.839 | 0.290 | 2.313 | 1.309-4.087 | 0.004 |
| ASMI 1SD | 0.539 | 0.213 | 1.714 | 1.128-2.606 | 0.012 |
| Normal | Reference |
Pain/discomfort | | | | | 0.465* |
| ASMI 2SD | 0.385 | 0.292 | 1.469 | 0.828-2.609 | 0.188 |
| ASMI 20 | 0.241 | 0.243 | 1.272 | 0.790-2.049 | 0.322 |
| ASMI 1SD | 0.113 | 0.180 | 1.120 | 0.786-1.595 | 0.530 |
| Normal | Reference |
Anxiety/depression | | | | 0.836* |
| ASMI 2SD | 0.140 | 0.352 | 1.150 | 0.576-2.295 | 0.691 |
| ASMI 20 | 0.277 | 0.374 | 1.319 | 0.633-2.750 | 0.460 |
| ASMI 1SD | 0.199 | 0.264 | 1.220 | 0.726-2.050 | 0.453 |
| Normal | Reference |
EQ5D index | | | | | 0.010* |
| ASMI 2SD | 0.656 | 0.247 | 1.928 | 1.187-3.132 | 0.008 |
| ASMI 20 | 0.622 | 0.212 | 1.863 | 1.229-2.824 | 0.003 |
| ASMI 1SD | 0.204 | 0.168 | 1.227 | 0.882-1.707 | 0.224 |
| Normal | reference |
Table 7
Multivariate analysis of five domains of EQ-5D and EQ5D index according to ASMI in older women
Mobility | | | | | 0.093* |
| ASMI 2SD | -1.407 | 0.826 | 0.245 | 0.048-1.240 | 0.089 |
| ASMI 1SD | 0.157 | 0.299 | 1.170 | 0.650-2.106 | 0.599 |
| ASMI 20 | -0.469 | 0.218 | 0.626 | 0.408-0.961 | 0.032 |
| Normal | | | | | |
Self-care | | | | | 0.974* |
| ASMI 2SD | -0.227 | 1.265 | 0.797 | 0.066-9.561 | 0.858 |
| ASMI 1SD | 0.136 | 0.360 | 1.146 | 0.565-2.325 | 0.705 |
| ASMI 20 | -0.042 | 0.288 | 0.959 | 0.544-1.689 | 0.884 |
| Normal | | | | | |
Usual activities | | | | 0.710* |
| ASMI 2SD | -0.111 | 1.354 | 0.895 | 0.063-12.791 | 0.935 |
| ASMI 1SD | 0.315 | 0.328 | 1.370 | 0.719-2.610 | 0.338 |
| ASMI 20 | -0.014 | 0.228 | 0.986 | 0.630-1.544 | 0.951 |
| Normal | | | | | |
Pain/discomfort | | | | | 0.299* |
| ASMI 2SD | -1.274 | 1.375 | 0.280 | 0.019-4.165 | 0.354 |
| ASMI 1SD | -0.082 | 0.287 | 0.921 | 0.524-1.619 | 0.775 |
| ASMI 20 | -0.306 | 0.192 | 0.737 | 0.505-1.074 | 0.112 |
| Normal | | | | | |
Anxiety/depression | | | | 0.754* |
| ASMI 2SD | -0.754 | 1.210 | 0.470 | 0.044-5.070 | 0.534 |
| ASMI 1SD | 0.177 | 0.309 | 1.194 | 0.651-2.190 | 0.566 |
| ASMI 20 | -0.248 | 0.279 | 0.780 | 0.451-1.349 | 0.374 |
| Normal | | | | | |
EQ5D index | | | | | 0.490* |
| ASMI 2SD | -1.828 | 1.427 | 0.161 | 0.010-2.652 | 0.201 |
| ASMI 1SD | 0.113 | 0.317 | 1.120 | 0.601-2.085 | 0.721 |
| ASMI 20 | -0.182 | 0.234 | 0.833 | 0.527-1.319 | 0.436 |
| Normal | | | | | |
Discussion
In this Korean national representative sample, the prevalences of low ASMI according to a cutoff point of ASMI 2SD were 9.7% and 0.7% for older (≥65 years) men and women, respectively, however, according to cutoff point of ASMI 1SD, 40.9% and 7.4% of the older men and women, respectively, had a low ASMI. In addition, only older men with a low ASMI were found to have a low health-related quality of life.
The means and SDs of ASMI were 7.14 ± 0.81 kg/m
2 and 5.89 ± 0.66 kg/m
2 in older Korean men and women, respectively, which are a little lower than those of previous studies. The New Mexico Elder Health Survey for Hispanic and non-Hispanic Americans conducted from May 1993 to September 1995 reported a mean ASMI was 7.7 ± 0.7 kg/m
2 in older men and 5.9 ± 0.7 kg/m
2 in older women [
13]. The Health ABC study on Americans conducted from 1997 to 1998 reported a mean ASMI in European Americans of 7.8 ± 0.9 kg/m
2 in older men and of 6.1 ± 0.8 kg/m
2 in older women [
21]. A Japanese study conducted from July 2002 to June 2003 reported mean ASMIs of 7.61 ± 0.7 kg/m
2 in older men and 6.32 ± 0.6 kg/m
2 in older women [
22]. Finally, a study in Taiwan published in 2013 reported mean ASMIs of 7.6 ± 0.8 kg/m
2 and 6.4 ± 0.6 kg/m
2 in older men and women, respectively [
23].
On the other hand, mean ASMIs in the young reference group in the present study were 7.81 ± 0.91 kg/m
2 and 5.67 ± 0.78 kg/m
2 in men and women, which are markedly lower than the values obtained in the American study, which reported mean ASMIs for a young reference group (18–40 years) of 8.6 ± 1.1 kg/m
2 and 7.3 ± 0.9 kg/m
2 in men and women [
13]. The present findings are also lower than those in the Taiwanese study, which reported mean ASMIs in a disease-free young reference group (20–40 years) of 8.2 ± 0.9 kg/m
2 and 5.9 ± 0.8 kg/m
2 in men and women [
23].
In The New Mexico Elder Health Survey for Hispanic and non-Hispanic Americans, the mean ASMIs of older men and women were approximately at the 87 and 80 percentiles, respectively, of the young reference group [
13]. In our study, the mean ASMIs of older men and women were at the 91 and 104 percentiles, of the young reference group, and the mean ASMI of older women was higher than the mean ASMI of the young woman reference group.
The proportion of older people with an ASMI two standard deviations below the mean ASMI of the young reference group also displayed a marked difference in the present study as compared with previously published values. In our study, older people with below ASMI 2SD were 9.7% in older men and 0.7% in older women, as compared to 13% at 61 to 70 years of age, 24% at 71 to 80 years of age, and 50% at aged 81 aged and older [
13], and 28% in men ≥70 years of age and 52% in women ≥70 years of age [
24].
Interestingly, many studies on sarcopenia in Asian populations have not used the standard ASMI cutoff of two standard deviations below the mean ASMI of the young reference group. The ASMI 1SD cutoff points used in Japanese and Korean studies were 6.53 kg/m
2 in men and 5.21 kg/m
2 in women and 7.09 kg/m
2 in men and 5.27 kg/m
2 in women, while a study in Taiwan used the lower 20 percentile values of gender specific healthy young age individuals [
22,
23,
25]. Considering the diagnostic criteria of sarcopenia recommended by the IWGS, EWGSOP, and AWGS, these sets of research standards are atypical. It is possible that the use of the ASMI 2SD value as a cutoff point in the aforementioned studies would have resulted in an unacceptably small proportion of sarcopenic older individuals. Other studies in Asians may have been similarly hampered.
A number of reasons can be suggested for the low proportions of older people with an ASMI 2SD below the mean ASMI of young reference groups in the present study. First, the body types of Koreans are changing due to improvements in living standards. According to the 2010 Size-Korea survey of body measurement, the average height of Koreans increased steadily up to 2003 and remained constant thereafter, whereas the body types of Koreans have consistently changed. In that survey, the proportion of body shape of Korean 20s women changed to 7.3-head units tall as compared with 20 years earlier a 7.2-head units tall, and leg lengths of Korean women were nearly 2 centimeters longer than 30 years earlier [
26]. Second, Korean women in their 20s and 30s can have poor weight reducing habits, and rely diet restriction rather than exercise. This reflects a distorted body image, with a desire to have a body type similar to Caucasian women, Korean women tend to prefer a slim body with focus on diet restriction, have a negative effect on muscle development [
27‐
29]. As a result, muscle mass in Korean women has been consistently reported to be decreasing more so than body fat because of repetitive low calorie diets and accompanying cycles of weight loss and weight gain [
27,
30,
31]. These results are consistent with the results of the Size-Korea survey, which found that mean BMI of subjects in their late 20s significantly decreased over time and the proportion of underweight individuals (as determined by BMI) increased to 15.7% in 2010 from 11.5% in 2003, while decreases in waist circumference was not significant over the same period [
26]. As a result, in the present study, the mean ASMI of the young reference women group was lower than the mean ASMI of the older women group (≥65 years of age) and the proportion of older women in the below ASMI 2SD group was excessively low.
Because ASMI values of the young reference group in the current study did not show a normal distribution, we used alternative values that corresponded to lowest 2.28% and 15.87% values in the young reference group in place of 1SD and 2SD values, respectively. After making this adjustment, the cutoff point of ASMI 2SD increased from 4.12 kg/m2 to 4.38 kg/m2 in older women, and had we applied the real ASMI 2SD value (4.12 kg/m2) only four older women would have had a low ASMI.
It is suggested that the existing sarcopenia diagnostic criteria using ASMI of a young reference group of the same gender and race is inadequate for Koreans. Considering clinical outcomes later in life, re-establishment of optimal ASMI cut-off points is needed.
We performed multivariate ordinal logistic regression analysis to examine the association between the low ASMI group based on the three established ASMI cutoff points mentioned and EQ-5D determined health-related quality of life. Low ASMI had significantly associated with poorer outcome of three domains of mobility, self-care, and usual activities among the five domains of the EQ-5D in older men. However, in older women with a low ASMI, these correlations were not significant for any of the three ASMI cutoff points. These findings are consistent with previous finding of a stronger correlation between sarcopenia and functional decline and disability in older men [
4]. Additional studies about gender-associated differences in muscle aging are needed.
Although the association between the low ASMI group based on ASMI 20 and any domain of EQ-5D was not significant in older women, the ASMI 20 cutoff point was significantly associated with EQ-5D in older men. On the other hand, the ASMI 2SD and ASMI 1SD cutoff points may not be adequate to diagnose sarcopenia in older Koreans because the proportions of older people with sarcopenia are quite variable. Studies are needed on the optimal ASMI cutoff point with respect to muscle function and clinical outcome for Koreans. We suggest that an ASMI 20 cutoff point (men 6.48 kg/m2, women 5.33 kg/m2) is appropriate for older people for the assessment of low ASM, until an optimal cutoff point is determined. Further studies on country/population specific ASMI cutoff point are needed in different communities.
This study had several strengths. First, our data were collected from a nationwide survey that reflected the community-dwelling Korean population. In particular, because the young reference group was large (2096 men and 2607 women) and was nationally representative, the ASMI distribution based on the young reference group can be considered reliable. Second, we performed analyses in a gender-specific manner. We found that the association between height-adjusted ASM and EQ-5D differed in older men and women, which is consistent with the findings of the recent FNIH study, in which height-adjusted ASM was found to be more useful for men and weight-adjusted ASM for women with respect skeletal muscle functions [
6], implying a possible underlying gender effect.
Finally, to our best knowledge, this study is the first report of a significant association between low ASMI and health-related quality of life. Our finding implies a possible relationship between sarcopenia and health-related quality of life, however, further studies are required to confirm the relation.
On the other hand, the present study has following limitations that warrant consideration. First, the study lacked investigation of cause-effect relationships because of its cross-sectional nature. Future prospective cohort studies are needed for such investigations. Second, previous studies analyzed ADL and IADL as dependent variables, whereas we used EQ-5D as a dependent variable. Although EQ-5D contains items similar to ADL and IADL, such as, mobility, self-care, and usual activities, direct comparisons might be inappropriate. Third, we did not consider muscle strength and muscle function and we used only height-adjusted ASM. The recent guidelines (EWGSOP, IWGS, AWGS and FNIH guideline) recommend to diagnose sarcopenia as reduced muscle mass related to muscle strength and function such as grip strength and gait speed, not only reduced muscle mass itself. However, our KNHANES data set did not contain information on muscle strength and muscle function, thus we have analysed only muscle mass in this study. Further studies are needed using our suggested ASM cutoff point and the FNIH guidelines, which represent the state of the art, recommend BMI-adjusted ASM. Finally, we did not include physical activity as a potential confounder because KNHANES IV and KNHANES V had different items of measurement. Further studies on the topic are needed.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
YPK, HSH and ILS conceptualized the study design. YPK conducted analyses. YPK, JYJ and SK wrote the first draft of the paper. All authors critically revised the manuscript and read and approved the final version.