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Disability Associated With Obesity, Dynapenia and Dynapenic-Obesity in Chinese Older Adults
JAMDA 15 (2014) 150.e11e150.e16
JAMDA journal homepage: www.jamda.com
Original Study
Disability Associated With Obesity, Dynapenia and Dynapenic-Obesity in Chinese Older Adults Ming Yang MD, Xiang Ding MS, Li Luo MD, Qiukui Hao MD, Birong Dong MD * The Center of Gerontology and Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan, China
a b s t r a c t Keywords: Disability obesity dynapenia dynapenic-obesity
Objectives: Whether the combination of obesity and low muscle strength (dynapenic-obesity) would cause greater impairment of the activities of daily living (ADL)/instrumental activities of daily living (IADL) than obesity alone and low muscle strength alone (dynapenia) remains unclear. The aim of this study was to reveal the possible independent and additive effects of dynapenia and obesity on ADL/IADL disability in an older Chinese population. Methods: A cross-sectional study, including 616 community-dwelling older adults, was conducted in China from 2010 to 2012. Based on the World Health Organization Asian Criteria of Obesity and handgrip strength tertiles, 4 independent groups were identified as follows: nondynapenia/nonobesity, dynapenia alone, obesity alone, and dynapenic-obesity. The Katz Index of Independence in ADL was used to assess ADL disability, whereas 6 IADL items of the Older Americans Resources and Services (OARS) multidimensional functional assessment questionnaire were used to assess IADL disability. Results: The prevalence of ADL and IADL disability was 21.1% and 28.9% in the dynapenic-obesity group, 15.5% and 22.6% in the dynapenia alone group, 13.1% and 19.6% in the obesity alone group, and 11.9% and 12.9% in the nondynapenia/nonobesity group, respectively. After adjusting for the covariates, in comparison with the dynapenic-obesity group, the adjusted odds ratios (95% confidence interval) for ADL disability were 0.36 (0.13e0.73) in the nondynapenia/nonobesity group, 0.51 (0.20e0.78) in the dynapenia-alone group, and 0.40 (0.11e0.61) in the obesity-alone group. The corresponding data for IADL disability were 0.55 (0.20e0.93), 0.82 (0.39e0.98), and 0.61 (0.30e0.91), respectively. Conclusion: Dynapenia, obesity, and dynapenic-obesity were associated with an increased risk of ADL/ IADL disability. Dynapenic-obesity was associated with a greater risk of ADL/IADL disability in comparison with dynapenia or obesity alone. Ó 2014 - American Medical Directors Association, Inc. All rights reserved.
The prevalence of obesity, a worldwide health problem, is increasing in all age groups, including the older population.1 The association between obesity and disability in older adults has been shown in a growing number of cross-sectional2,3 and longitudinal studies.4,5 Regardless of the method of measuring disability, these studies conclude that obesity is related to disability. In addition to obesity, another important aspect of age-related change in body composition is age-related loss of muscle mass, which was termed sarcopenia by Rosenberg in 1989.6 People rely on This study was funded by the National Department Public Benefit Research Foundation by the Ministry of Health P. R. China (No. 201002011). The sponsor has no role in the design, methods, data collection, analysis and preparation of the paper. Drs. Yang and Ding contributed equally to this work. The authors declare no conflicts of interest. * Address correspondence to Birong Dong, MD, Department of Geriatrics, West China Hospital of Sichuan University, 37 Guoxue Lane, Chengdu, China. E-mail address: [email protected] (B. Dong).
skeletal muscles for every movement and activity of daily life (ADL), and sarcopenia is understandably associated with functional limitation and disability. There is evidence7 to support this view, but other studies8e10 do not support the association between sarcopenia and disability. Muscle mass and muscle strength decrease with advancing age, and muscle strength is not solely dependent on muscle mass.11 The age-related changes in muscle mass can explain less than 5% of the variance in muscle strength.12 Recently, Manini and Clark13 summarized the results of 16 studies that addressed the relationship between muscle mass or muscle strength and disability or mortality, and found that age-related loss of muscle strength is a more consistent risk for disability and mortality than loss of muscle mass. They coined the term “dynapenia” to describe age-related loss of muscle strength.13,14 Based on the concept of dynapenia, another new concept, dynapenic-obesity, emerged, and it refers to the combination of obesity and dynapenia. Obesity and dynapenia are associated with
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M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16
disability in older adults, and it would be rational to hypothesize that older adults with dynapenic-obesity would have greater functional impairments than those with obesity or dynapenia alone. There are limited data addressing this hypothesis, but in a longitudinal study, Stenholm and colleagues15 found that older people with obesity in the lowest leg strength tertile had a greater decline in mobility than the other participants. To the best of our knowledge, no study has addressed the effect of obesity, dynapenia, and dynapenic-obesity on disability in ADLs and instrumental ADLs (IADLs) in Chinese older adults. We conducted this study to reveal the potential effects of dynapenia and obesity on ADL/IADL disability in an older Chinese population. Methods Study Population The participants were from the Comprehensive Geriatric Assessment and Health Care Service System in Chinese Elderly Project. This cross-sectional study was conducted in 2 cities (Chengdu and Suining) in Sichuan province in China. From Oct 2010 to Aug 2012, 887 community-dwelling persons from Chengdu or Suining, aged 60 years and older, were included in this survey. This study protocol was approved by the Research Ethics Committee of Sichuan University and informed consent was obtained from all the participants (or their legal proxies). All interviewers were trained by using investigation manuals, multimedia materials, and simulated patients. Each interviewer needed to pass the test before the formal investigation. Trained personnel visited and evaluated all the study participants at their homes or community centers for data collection. The anthropometric measurements were performed by trained personnel, and biological specimens were collected. Anthropometric Measures Body height and weight were measured using a wall-mounted stadiometer and a digital floor scale to the nearest 0.1 cm and 0.1 kg respectively. The body mass index (BMI: body weight [kg]/ height2 [m2]) was calculated. Using a steel measuring tape (Reynolds; Baofeng Inc, Ningbo, China), the waist circumference (WC) was measured to the nearest 0.1 cm; the measurement was taken on bare skin following a light expiration, with the participant standing. Measurement of Hand Grip Strength Handgrip strength (in kg) was measured by a handheld dynamometer based on strain gauge sensors (EH101; Xiangshan Inc, Guangdong, China). Both hands were tested with the participant seated, elbow flexed at a 110 angle, with the wrist in a neutral position, and the interphalangeal joint of the index finger at a 90 angle. Two readings were taken, and the highest value was used for the analysis. We conducted a preliminary study to evaluate the reliability of the handgrip strength test using the intraclass correlation coefficient (ICC). The result indicated that the test-retest reliability of the handgrip strength test was excellent (ICC ¼ 0.85, n ¼ 115). Classification of Obesity, Dynapenia, and Dynapenic-Obesity According to the World Health Organization Asian Criteria of Obesity,16 the participants represented either the nonobesity group (<25 kg/m2) or the obesity group (25 kg/m2). Muscle strength significantly differs by age and gender,17 so the handgrip strength values were regressed to a full cubic polynomial by age (age, age2, and age3) in the within-sex subgroups using a forward stepwise
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regression. The standardized residuals were retained to represent the age-adjusted values.18 The sex-specific tertiles of handgrip strength were calculated, and the participants in the lowest tertile of handgrip strength were grouped as dynapenic, whereas those in the second and the third tertiles were grouped as nondynapenic. The individuals were classified into the following 4 groups based on sex-specific age-adjusted handgrip strength and BMI: “dynapeniaalone,” “obesity-alone,” “dynapenic-obesity,” and “nondynapenia/ nonobesity.” Measurement of ADL and IADL Disability The functional status of each participant was evaluated by trained interviewers. The Katz Index of Independence in ADL,19 which included 6 items (bathing, dressing, toileting, transferring, continence, and feeding), was used to assess ADLs. The response to each item was “independent” (1 point) or “partly or completely dependent” (0 points). Six IADL items (public transportation, shopping, food preparation, housekeeping, responsibility for own medications, and handling finances) in the Older Americans Resources and Services (OARS) multidimensional functional assessment questionnaire 20 were used to assess IADLs. The response to each item was “without help” (2 points), “with some help” (1 point), and “completely unable to do” (0 points). The validity and reliability of the scales have been well established.20e22 The participants were defined as having an ADL or IADL disability when they reported a need for help from another person in performing at least one ADL questionnaire item (ADL disability) or one IADL questionnaire item (IADL disability). Assessment of Covariates The covariates in the analyses were age, gender, smoking status (current smoker, former smoker, and nonsmoker), alcohol intake status (current drinker, former drinker, and nondrinker), and education level (less than high school, high school, and more than high school). Physical activity was assessed by self-reporting. The participants were asked about the frequency and duration of physical activities of at least moderate intensity in the previous month. According to this information, the participants were classified into 3 groups (none, <30 minutes per day, 30 minutes per day). The following chronic conditions, which were potentially related to disability, were assessed by trained interviewers using a self-reported questionnaire: visual problems, hearing problems, arthritis, diabetes, lung disease (chronic bronchitis/emphysema or asthma), cardiovascular disease (hypertension, coronary heart disease, or chronic heart failure), central nervous system disease (stroke or dementia), and tumor. Statistical Analysis The statistical analyses were performed with the SPSS for Windows software package, version 11.5 (SPSS Inc, Chicago, IL). The continuous data are presented as unadjusted means SD, whereas the categorical variables are presented as percentage. The general linear models (GLMs) were applied to identify the difference in the continuous data among the 4 groups. Bonferroni post hoc analyses were performed to identify the group differences. Logistic regression models were applied to identify the differences for the dichotomized variables. All the regressions were adjusted for age, gender, alcohol intake status, smoking status, physical activity levels (min/d), and the chronic conditions mentioned previously. Because BMI and WC were highly correlated (Spearman correlation coefficient: 0.62), we further adjusted WC in Model 2. All P values were 2-sided, and significance was accepted at P less than .05.
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M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16
Results In total, 616 participants were included in the analyses, whereas 271 participants had missing data for handgrip strength or WC and were excluded from our analyses. The individuals selected for this study were similar in age (70.7 6.8 vs 69.8 7.2 years), gender (58.4% vs 56.1% women), and the prevalence of obesity (23.5% vs 22.9%) and ADL (10.7% vs 10.2%) or IADL disability (15.9% vs 15.3%) compared with those who were excluded. All of the participants were Han Chinese. General Characteristics According to the Dynapenia and Obesity Status Table 1 shows the general characteristics of the participants according to their dynapenia and obesity status. There was no significant difference across the 4 groups with respect to age, gender, the percentage of current smokers or current drinkers, and the percentage of participants who did physical activity 30 minutes per day. The mean sum of the chronic conditions was significantly greater in the obesity-alone group (1.9) than in the dynapenia-alone group (1.4) or the nondynapenia/nonobesity group (1.5) (P < .01). No significant difference was found between the dynapenic-obesity group and the other 3 groups (P < .05). Because of the study design, the obesity-alone and dynapenic-obesity groups had greater BMI and WC than the other 2 groups for men or women (P < .01). The dynapenia-alone and dynapenic-obesity groups exhibited lower handgrip strength than the other 2 groups for both sexes (P < .01). As expected by study design, there was no significant difference in the BMI and WC between the obesity-alone and the dynapenic-obesity groups in both sexes (P < .05). Similarly, there was no significant difference in handgrip strength between the dynapenia-alone and the dynapenic-obesity groups in men or women (P < .05). ADL Disability According to Dynapenia and Obesity Status The prevalence of ADL disability was 21.1% in the dynapenicobesity group, 15.5% in the dynapenia-alone group, 13.1% in the obesity-alone group, and 11.9% in the nondynapenia/nonobesity group. After adjusting for the covariates, with comparison to the dynapenic-obesity group, the adjusted odds ratios (95% confidence interval) for ADL disability were 0.36 (0.13e0.73) in the nondynapenia/nonobesity group, 0.51 (0.20e0.78) in the dynapeniaalone group, and 0.40 (0.11e0.61) in the obesity-alone group. As illustrated in Table 2, disability according to each item of the Katz
Index of Independence in ADL was compared across the 4 groups. The dynapenic-obesity group had the highest proportion of disability in each item, whereas the nondynapenia/nonobesity group had the lowest proportion, although no significant differences were identified with respect to disability in feeding and disability in continence disability. With comparison to the dynapenic-obesity group, a significant lower prevalence of disability was found in the dynapenia-alone or the obesity-alone group with respect to bathing, dressing, transferring, and toileting; the differences were not significant across the 3 groups in feeding and continence.
IADL Disability According to Dynapenia and Obesity Status The prevalence of IADL disability was 28.9% in the dynapenicobesity group, 22.6% in the dynapenia-alone group, 19.6% in the obesity-alone group, and 12.9% in the nondynapenia/nonobesity group. After adjusting for the covariates, with comparison with the dynapenic-obesity group, the adjusted odds ratios for IADL disability were 0.55 (0.20e0.93) in the nondynapenia/nonobesity group, 0.82 (0.39e0.98) in the dynapenia-alone group, and 0.61 (0.30e0.91) in the obesity-alone group. As illustrated in Table 2, disability in each IADL item of the OARS multidimensional functional assessment questionnaire was compared across the 4 groups. The dynapenicobesity group had the highest proportion of disability in each item, whereas the nondynapenia/nonobesity group had the lowest proportion (exception: responsibility for own medications and handling finances). No significant differences were found between the dynapenic-obesity group and the nondynapenia/nonobesity group with respect to the participant’s responsibility for his or her own medications and handling finances. In comparison with the dynapenic-obesity group, a significantly lower prevalence of disability was found in the dynapenia-alone or the obesity-alone group with respect to public transportation, shopping, food preparation, and housekeeping.
Discussion To the best of our knowledge, this study is the first to address the effect of obesity, dynapenia, and their combination on ADL/IADL disability in older Chinese adults. Our study indicates that older adults with dynapenia alone, obesity alone, or dynapenic-obesity had a higher prevalence of ADL and IADL disability in comparison with those without these conditions. Older adults with dynapenic-obesity
Table 1 Characteristics of Groups According to Obesity and Dynapenia Status Nondynapenia and Nonobesity n ¼ 303 Age, y Female, % Body mass index, kg/m2 Waist circumference male, cm Waist circumference female, cm Handgrip strength male, kg Handgrip strength female, kg Current smoker, % Current drinker, % Physical activity 30 min/d, % Sum of chronic conditions, 0e8
70.8 57.8 21.7 80.2 76.6 33.5 21.4 15.8 13.5 62.0 1.5x
7.1
2.1*,y 6.6*,y 7.3*,y 5.7*,y,x 5.0y,x
Dynapenia Alone n ¼ 168 71.2 59.5 21.4 78.8 76.8 19.8 10.5 11.3 19.6 58.3 1.4*
7.0
2.6*,y 6.4*,y 8.7*,y 6.7*,z 4.2*,z
Obesity Alone n ¼ 107
Dynapenic-Obesity n ¼ 38
69.9 59.8 27.0 90.6 88.4 36.9 23.0 14.9 15.9 62.6 1.9z,x
69.2 55.3 27.4 92.0 89.5 21.2 13.2 5.2 15.8 57.9 1.7
5.9 2.1z,x 8.6z,x 10.4z,x 5.7y,z,x 5.6y,x
6.4
2.1z,x 5.0z,x 6.7z,x 6.9*,z 3.5*,z
Categorical variables are presented as prevalence, whereas continuous data are presented as unadjusted mean SD. For categorical variables, Logistic regression models were used to identify any group difference among the 4 groups. For continuous data, general linear models were used to identify difference among the 4 groups and Bonferroni post hoc analyses were used to identify any group difference. Significance was accepted at P < .05. *Significantly different from obesity alone. y Significantly different from dynapenic-obesity. z Significantly different from non-dynapenia and non-obesity. x Significantly different from dynapenia alone.
M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16
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Table 2 Activity of Daily Living/Instrumental Activity of Daily Living Disability According to Obesity and Dynapenia Status
ADL disability Prevalence, % Model 1 Model 2 Bathing* Prevalence, % Model 1 Model 2 Dressing* Prevalence, % Model 1 Model 2 Feeding* Prevalence, % Model 1 Model 2 Transferring* Prevalence, % Model 1 Model 2 Continence* Prevalence, % Model 1 Model 2 Toileting* Prevalence, % Model 1 Model 2 IADL disability Prevalence, % Model 1 Model 2 Public transportation* Prevalence, % Model 1 Model 2 Shopping* Prevalence, % Model 1 Model 2 Food preparation* Prevalence, % Model 1 Model 2 Housekeeping* Prevalence, % Model 1 Model 2 Responsibility for own medications* Prevalence, % Model 1 Model 2 Handling finances* Prevalence, % Model 1 Model 2
Nondynapenia/ Nonobesity n ¼ 303
Dynapenia Alone n ¼ 168
Obesity Alone n ¼ 107
Dynapenic-Obesity n ¼ 38
11.9 0.41 (0.15e0.87) 0.36 (0.13e0.73)
15.5 0.54 (0.14e0.85) 0.51 (0.20e0.78)
13.1 0.42 (0.12e0.66) 0.40 (0.11e0.61)
21.1 1 1
4.0 0.47 (0.13e0.72) 0.45 (0.19e0.73)
4.7 0.81 (0.58e0.91) 0.78 (0.56e0.98)
4.6 0.68 (0.41e0.92) 0.67 (0.36e0.98)
5.3 1 1
1.7 0.52 (0.13e0.78) 0.58 (0.15e0.84)
2.4 0.61 (0.25e0.88) 0.65 (0.30e0.93)
1.9 0.55 (0.14e0.87) 0.60 (0.22e0.82)
2.6 1 1
2.3 0.76 (0.04e4.89) 0.70 (0.01e3.02)
2.4 0.88 (0.06e7.84) 0.81 (0.03e4.98)
1.9 0.63 (0.25e8.11) 0.61 (0.08e9.45)
2.6 1 1
1.7 0.17 (0.08e0.68) 0.24 (0.12e0.72)
1.8 0.29 (0.02e0.53) 0.35 (0.09e0.57)
1.9 0.30 (0.04e0.58) 0.34 (0.05e0.62)
5.3 1 1
8.6 0.75 (0.20e2.18) 0.79 (0.18e2.58)
8.3 0.70 (0.18e2.21) 0.78 (0.17e2.57)
8.4 0.74 (0.18e2.32) 0.79 (0.20e2.45)
10.5 1 1
0.7 0.22 (0.08e0.75) 0.15 (0.06e0.51)
1.8 0.32 (0.10e0.52) 0.28 (0.15e0.48)
1.9 0.36 (0.12e0.54) 0.33 (0.17e0.67)
5.3 1 1
12.9 0.41 (0.17e0.88) 0.55 (0.20e0.93)
22.6 0.78 (0.42e0.90) 0.82 (0.39e0.98)
19.6 0.61 (0.31e0.88) 0.61 (0.30e0.91)
28.9 1 1
5.9 0.32 (0.11e0.68) 0.48 (0.08e0.72)
11.3 0.56 (0.22e0.87) 0.62 (0.13e0.92)
13.7 0.57 (0.18e0.86) 0.68 (0.32e0.90)
15.8 1 1
5.3 0.42 (0.08e0.61) 0.41 (0.12e0.65)
10.7 0.69 (0.24e0.86) 0.61 (0.11e0.88)
10.9 0.69 (0.15e0.91) 0.62 (0.18e0.88)
15.8 1 1
5.3 0.38 (0.09e0.65) 0.32 (0.11e0.68)
6.5 0.42 (0.15e0.66) 0.38 (0.13e0.57)
10.3 0.72 (0.23e0.93) 0.67 (0.13e0.88)
15.8 1 1
6.6 0.40 (0.12e0.82) 0.35 (0.11e0.89)
12.5 0.75 (0.43e0.91) 0.71 (0.40e0.93)
10.3 0.66 (0.22e0.82) 0.61 (0.30e0.88)
15.8 1 1
5.0 0.49 (0.21e2.69) 0.52 (0.19e2.35)
5.4 0.51 (0.11e3.34) 0.54 (0.08e2.87)
4.7 0.41 (0.08e1.36) 0.38 (0.07e1.32)
10.5 1 1
4.3 0.69 (0.36e1.38) 0.74 (0.23e1.52)
6.5 0.75 (0.23e2.97) 0.80 (0.31e3.12)
3.7 0.62 (0.28e1.11) 0.65 (0.23e1.08)
5.3 1 1
IADL, instrumental activity of daily living. Data are presented as prevalence (%) and odds ratio (95% confidence interval). Model 1: adjusted for age, gender, race, alcohol intake status, smoking status, physical activity, and 8 chronic conditions (visual problems, hearing problems, arthritis, diabetes, lung disease, cardiovascular disease, central nervous system disease, and tumor). Model 2: further adjusted for waist circumference on the basis of Model 1. *Disability was defined as “need for any help from another person.”
had a higher prevalence of ADL and IADL disability than those with dynapenia or obesity alone. Most of the current studies that examine the independent and additive effects of obesity and muscle on function or disability focus on sarcopenic-obesity rather than dynapenic-obesity.2,23e26 The results of these sarcopenic-obesity studies are not consistent with each other, and some,23,27 but not all, of the studies concluded that
sarcopenic-obesity was associated with a greater risk of functional impairment or disability than obesity alone. Only a small number of studies15,18,28 addressed the effects of dynapenic-obesity on disability, and all of them concerned mobility disability. All the dynapenicobesity studies15,18,28 concluded that dynapenic-obesity was associated with a greater risk of mobility disability than obesity alone. The disagreement between the sarcopenic-obesity and dynapenic-obesity
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studies may be explained by the hypothesis that muscle strength, instead of “simply muscle mass,” is a critical risk factor of physical disability. This hypothesis has been supported by a systematic review by Manini and Clark,13 but further evidence is needed to draw a strong conclusion. It is notable that the term “sarcopenia,” which was initially defined as the age-related loss of muscle mass,6 was recommended to be synonymous with the age-related loss of muscle strength and function in a recent statement of the European Working Group on Sarcopenia in Older People (EWGSOP).29 In that case, the newer definition of sarcopenia seems to include the term “dynapenia.” However, a global consensus on the definition of sarcopenia has not been achieved.13,14 We argue that loss of muscle strength and loss of muscle mass need to be defined independently. As suggested by Manini and Clark,13 the term “sarcopenia” should be used in its original context to describe the age-related loss of muscle mass, whereas the term “dynapenia” should be used to describe the agerelated loss of muscle strength. First, loss of muscle strength in older people is weakly associated with loss of muscle mass.11 In fact, the decline in muscle strength is much more rapid than the concomitant loss of muscle mass.11 Further, maintaining or gaining muscle mass could not prevent aging-related loss of muscle strength.30 Second, a systematic review of 16 studies found that muscle strength, instead of muscle mass, is the critical factor for determining disability and mortality in the elderly.13 Our study indicates that dynapenia alone and obesity alone were associated with ADL disability. The association between obesity and ADL disability has been supported by a large body of evidence.19,22,24,31,32 There are studies reporting the relationship between dynapenia (measured with hand grip strength) and ADLs. In a 7-year prospective cohort study, handgrip strength was found to be an independent predictor of ADL disability among older Mexican Americans.32 In addition, Davis et al33 indicated that strength and BMI were associated positively and negatively with ADL disability, respectively. Our finding is consistent with the Davis et al33 study, but we found that dynapenic-obesity has a more negative effect on ADL than dynapenia alone or obesity alone. Our study indicates that dynapenia alone, obesity alone, and dynapenic-obesity had negative effects on IADLs, and the effect of dynapenic-obesity was greater than that of the other 2 conditions. The association between obesity and IADLs has been supported by some studies.5,34 Dynapenia (measured by handgrip and quadriceps strength) was associated with physical disability in IADL and functional limitation in a recent cross-sectional study.35 To our knowledge, no study is examining the effect of dynapenic-obesity on IADL disability. Skeletal muscle is essential for movement and ADLs/IADLs. Theoretically, a certain minimum level of muscle strength is needed to perform specific daily tasks, such as walking, feeding, and toileting. It is difficult to define this minimum threshold level, because it varies significantly from person to person and may be influenced by many internal (eg, posture or body weight) or external (eg, with or without assistive devices) factors. Based on daily experience, more strength is essential to complete some daily activities (eg, housekeeping) than others (eg, feeding). The present study found no significant differences across the 4 groups in terms of feeding, continence, responsibility for own medications, and handling finances. The reason might be that the minimum level of muscle strength for these tasks is relatively lower than that for other tasks (eg, housekeeping and shopping). Although Manini and Clark13 suggested that handgrip strength should be used as a screening test for dynapenia, whereas knee extensor strength is an advanced test for defining dynapenia, no consensus has been reached. We used handgrip strength to measure
dynapenia in this study for 2 reasons. First, it has been shown that handgrip strength is a good indicator of whole body strength, whereas low hand grip strength is consistently associated with a greater likelihood of mortality, the development of mobility disability, and an increased risk of complications.36 There is evidence that handgrip strength provided risk estimates similar to those of quadriceps strength.37 Second, in comparison with knee extensor strength, handgrip strength is easier to measure and the device is significantly less expensive and affordable for developing countries, such as China. There is no consensus on the cut point of handgrip strength or knee extensor strength to define dynapenia. In our study, we calculated the age-adjusted and sex-specific tertiles of hand grip strength, and defined individuals in the lowest tertile as those with dynapenia. This method has been used in other studies,18,38 although it is arbitrary. There are several limitations to this study. First, a causal effect association could not be established because of the cross-sectional design. Second, approximately 30% of the individuals were excluded from the analyses because of missing data that might induce selection bias, although the gender and mean age were very similar between the included and excluded population. Third, comparisons with other studies are difficult because the definition and standardized measurement of dynapenia have not been established. In conclusion, dynapenia alone, obesity alone, and dynapenicobesity were associated with an increased risk of ADL/IADL disability. Dynapenic-obesity was associated with a greater risk of ADL/IADL disability in comparison with dynapenia alone or obesity alone. Reference 1. Samper-Ternent R, Al Snih S. Obesity in older adults: Epidemiology and implications for disability and disease. Rev Clin Gerontol 2012;22:10e34. 2. Woo J, Leung J, Kwok T. BMI, body composition, and physical functioning in older adults. Obesity (Silver Spring) 2007;15:1886e1894. 3. Chen H, Guo X. Obesity and functional disability in elderly Americans. J Am Geriatr Soc 2008;56:689e694. 4. Al Snih S, Ottenbacher KJ, Markides KS, et al. The effect of obesity on disability vs mortality in older Americans. Arch Intern Med 2007;167:774e780. 5. Wee CC, Huskey KW, Ngo LH, et al. Obesity, race, and risk for death or functional decline among medicare beneficiaries: A cohort study. Ann Intern Med 2011;154:645e655. 6. Rosenberg I. Summary comments. Am J Clin Nutr 1989;50:1231e1233. 7. Janssen I, Heymsfield SB, Ross R. Low relative skeletal muscle mass (sarcopenia) in older persons is associated with functional impairment and physical disability. J Am Geriatr Soc 2002;50:889e896. 8. Visser M, Harris TB, Langlois J, et al. Body fat and skeletal muscle mass in relation to physical disability in very old men and women of the Framingham Heart Study. J Gerontol A Biol Sci Med Sci 1998;53:M214eM221. 9. Visser M, Langlois J, Guralnik JM, et al. High body fatness, but not low fat-free mass, predicts disability in older men and women: The cardiovascular health study. Am J Clin Nutr 1998;68:584e590. 10. Delmonico MJ, Harris TB, Lee JS, et al. Alternative definitions of sarcopenia, lower extremity performance, and functional impairment with aging in older men and women. J Am Geriatr Soc 2007;55:769e774. 11. Mitchell WK, Williams J, Atherton P, et al. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Front Physiol 2012;3:260. 12. Hughes VA, Frontera WR, Wood M, et al. Longitudinal muscle strength changes in older adults: Influence of muscle mass, physical activity, and health. J Gerontol A Biol Sci Med Sci 2001;56:B209eB217. 13. Manini TM, Clark BC. Dynapenia and aging: An update. J Gerontol A Biol Sci Med Sci 2012;67:28e40. 14. Clark BC, Manini TM. Sarcopenia ¼/¼ dynapenia. J Gerontol A Biol Sci Med Sci 2008;63:829e834. 15. Stenholm S, Alley D, Bandinelli S, et al. The effect of obesity combined with low muscle strength on decline in mobility in older persons: Results from the InCHIANTI Study. Int J Obes (Lond) 2009;33:635e644. 16. WHO, IASO, and IOTF. The Asia-Pacific Perspective: Redefining Obesity and its Treatment. Sydney: Health Communications Australia Pty Limited; 2000, p. 18. 17. Kallman DA, Plato CC, Tobin JD. The role of muscle loss in the age-related decline of grip strength: Cross-sectional and longitudinal perspectives. J Gerontol 1990;45:M82eM88. 18. Bouchard DR, Janssen I. Dynapenic-obesity and physical function in older adults. J Gerontol A Biol Sci Med Sci 2010;65:71e77.
M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16 19. Katz S, Downs TD, Cash HR, Grotz RC. Progress in development of the index of ADL. Gerontologist 1970;10:20e30. 20. Fillenbaum GG, Smyer MA. The development, validity, and reliability of the OARS multidimensional functional assessment questionnaire. J Gerontol 1981; 36:428e434. 21. McDowell I. Measuring Health: A Guide to Rating Scales and Questionnaires. 3rd ed. New York: Oxford University Press; 2006. 22. Doble SE, Fisher AG. The dimensionality and validity of the Older Americans Resources and Services (OARS) Activities of Daily Living (ADL) Scale. J Outcome Meas 1998;2:4e24. 23. Rolland Y, Lauwers-Cances V, Cristini C, et al. Difficulties with physical function associated with obesity, sarcopenia, and sarcopenic-obesity in communitydwelling elderly women: The EPIDOS (EPIDemiologie de l’OSteoporose). Study. Am J Clin Nutr 2009;89:1895e1900. 24. Sternfeld B, Ngo L, Satariano WA, Tager IB. Associations of body composition with physical performance and self-reported functional limitation in elderly men and women. Am J Epidemiol 2002;156:110e121. 25. Villareal DT, Banks M, Siener C, et al. Physical frailty and body composition in obese elderly men and women. Obes Res 2004;12:913e920. 26. Carmeli E, Imam B, Merrick J. The relationship of pre-sarcopenia (low muscle mass) and sarcopenia (loss of muscle strength) with functional decline in individuals with intellectual disability (ID). Arch Gerontol Geriatr 2012;55: 181e185. 27. Baumgartner RN, Wayne SJ, Waters DL, et al. Sarcopenic obesity predicts instrumental activities of daily living disability in the elderly. Obes Res 2004; 12:1995e2004. 28. Stenholm S, Rantanen T, Heliovaara M, Koskinen S. The mediating role of Creactive protein and handgrip strength between obesity and walking limitation. J Am Geriatr Soc 2008;56:462e469.
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29. Cruz-Jentoft AJ, Baeyens JP, Bauer JM, et al. Sarcopenia: European consensus on definition and diagnosis: Report of the European Working Group on Sarcopenia in Older People. Age Ageing 2010;39:412e423. 30. Delmonico MJ, Harris TB, Visser M, et al. Longitudinal study of muscle strength, quality, and adipose tissue infiltration. Am J Clin Nutr 2009;90: 1579e1585. 31. Crosby CA, Wehbe MA, Mawr B. Hand strength: normative values. J Hand Surg Am 1994;19:665e670. 32. Al Snih S, Markides KS, Ottenbacher KJ, Raji MA. Hand grip strength and incident ADL disability in elderly Mexican Americans over a seven-year period. Aging Clin Exp Res 2004;16:481e486. 33. Davis JW, Ross PD, Preston SD, et al. Strength, physical activity, and body mass index: Relationship to performance-based measures and activities of daily living among older Japanese women in Hawaii. J Am Geriatr Soc 1998;46: 274e279. 34. Na YM, Park HA, Kang JH, et al. Obesity, obesity related disease, and disability. Korean J Fam Med 2011;32:412e422. 35. Hairi NN, Cumming RG, Naganathan V, et al. Loss of muscle strength, mass (sarcopenia), and quality (specific force) and its relationship with functional limitation and physical disability: The concord health and ageing in men project. J Am Geriatr Soc 2010;58:2055e2062. 36. Bohannon RW. Hand-grip dynamometry predicts future outcomes in aging adults. J Geriatr Phys Ther 2008;31:3e10. 37. Newman AB, Kupelian V, Visser M, et al. Strength, but not muscle mass, is associated with mortality in the health, aging and body composition study cohort. J Gerontol A Biol Sci Med Sci 2006;61:72e77. 38. Senechal M, Dionne IJ, Brochu M. Dynapenic abdominal obesity and metabolic risk factors in adults 50 years of age and older. J Aging Health 2012;24: 812e826.
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Original Study
Disability Associated With Obesity, Dynapenia and Dynapenic-Obesity in Chinese Older Adults Ming Yang MD, Xiang Ding MS, Li Luo MD, Qiukui Hao MD, Birong Dong MD * The Center of Gerontology and Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan, China
a b s t r a c t Keywords: Disability obesity dynapenia dynapenic-obesity
Objectives: Whether the combination of obesity and low muscle strength (dynapenic-obesity) would cause greater impairment of the activities of daily living (ADL)/instrumental activities of daily living (IADL) than obesity alone and low muscle strength alone (dynapenia) remains unclear. The aim of this study was to reveal the possible independent and additive effects of dynapenia and obesity on ADL/IADL disability in an older Chinese population. Methods: A cross-sectional study, including 616 community-dwelling older adults, was conducted in China from 2010 to 2012. Based on the World Health Organization Asian Criteria of Obesity and handgrip strength tertiles, 4 independent groups were identified as follows: nondynapenia/nonobesity, dynapenia alone, obesity alone, and dynapenic-obesity. The Katz Index of Independence in ADL was used to assess ADL disability, whereas 6 IADL items of the Older Americans Resources and Services (OARS) multidimensional functional assessment questionnaire were used to assess IADL disability. Results: The prevalence of ADL and IADL disability was 21.1% and 28.9% in the dynapenic-obesity group, 15.5% and 22.6% in the dynapenia alone group, 13.1% and 19.6% in the obesity alone group, and 11.9% and 12.9% in the nondynapenia/nonobesity group, respectively. After adjusting for the covariates, in comparison with the dynapenic-obesity group, the adjusted odds ratios (95% confidence interval) for ADL disability were 0.36 (0.13e0.73) in the nondynapenia/nonobesity group, 0.51 (0.20e0.78) in the dynapenia-alone group, and 0.40 (0.11e0.61) in the obesity-alone group. The corresponding data for IADL disability were 0.55 (0.20e0.93), 0.82 (0.39e0.98), and 0.61 (0.30e0.91), respectively. Conclusion: Dynapenia, obesity, and dynapenic-obesity were associated with an increased risk of ADL/ IADL disability. Dynapenic-obesity was associated with a greater risk of ADL/IADL disability in comparison with dynapenia or obesity alone. Ó 2014 - American Medical Directors Association, Inc. All rights reserved.
The prevalence of obesity, a worldwide health problem, is increasing in all age groups, including the older population.1 The association between obesity and disability in older adults has been shown in a growing number of cross-sectional2,3 and longitudinal studies.4,5 Regardless of the method of measuring disability, these studies conclude that obesity is related to disability. In addition to obesity, another important aspect of age-related change in body composition is age-related loss of muscle mass, which was termed sarcopenia by Rosenberg in 1989.6 People rely on This study was funded by the National Department Public Benefit Research Foundation by the Ministry of Health P. R. China (No. 201002011). The sponsor has no role in the design, methods, data collection, analysis and preparation of the paper. Drs. Yang and Ding contributed equally to this work. The authors declare no conflicts of interest. * Address correspondence to Birong Dong, MD, Department of Geriatrics, West China Hospital of Sichuan University, 37 Guoxue Lane, Chengdu, China. E-mail address: [email protected] (B. Dong).
skeletal muscles for every movement and activity of daily life (ADL), and sarcopenia is understandably associated with functional limitation and disability. There is evidence7 to support this view, but other studies8e10 do not support the association between sarcopenia and disability. Muscle mass and muscle strength decrease with advancing age, and muscle strength is not solely dependent on muscle mass.11 The age-related changes in muscle mass can explain less than 5% of the variance in muscle strength.12 Recently, Manini and Clark13 summarized the results of 16 studies that addressed the relationship between muscle mass or muscle strength and disability or mortality, and found that age-related loss of muscle strength is a more consistent risk for disability and mortality than loss of muscle mass. They coined the term “dynapenia” to describe age-related loss of muscle strength.13,14 Based on the concept of dynapenia, another new concept, dynapenic-obesity, emerged, and it refers to the combination of obesity and dynapenia. Obesity and dynapenia are associated with
1525-8610/$ - see front matter Ó 2014 - American Medical Directors Association, Inc. All rights reserved. http://dx.doi.org/10.1016/j.jamda.2013.10.009
M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16
disability in older adults, and it would be rational to hypothesize that older adults with dynapenic-obesity would have greater functional impairments than those with obesity or dynapenia alone. There are limited data addressing this hypothesis, but in a longitudinal study, Stenholm and colleagues15 found that older people with obesity in the lowest leg strength tertile had a greater decline in mobility than the other participants. To the best of our knowledge, no study has addressed the effect of obesity, dynapenia, and dynapenic-obesity on disability in ADLs and instrumental ADLs (IADLs) in Chinese older adults. We conducted this study to reveal the potential effects of dynapenia and obesity on ADL/IADL disability in an older Chinese population. Methods Study Population The participants were from the Comprehensive Geriatric Assessment and Health Care Service System in Chinese Elderly Project. This cross-sectional study was conducted in 2 cities (Chengdu and Suining) in Sichuan province in China. From Oct 2010 to Aug 2012, 887 community-dwelling persons from Chengdu or Suining, aged 60 years and older, were included in this survey. This study protocol was approved by the Research Ethics Committee of Sichuan University and informed consent was obtained from all the participants (or their legal proxies). All interviewers were trained by using investigation manuals, multimedia materials, and simulated patients. Each interviewer needed to pass the test before the formal investigation. Trained personnel visited and evaluated all the study participants at their homes or community centers for data collection. The anthropometric measurements were performed by trained personnel, and biological specimens were collected. Anthropometric Measures Body height and weight were measured using a wall-mounted stadiometer and a digital floor scale to the nearest 0.1 cm and 0.1 kg respectively. The body mass index (BMI: body weight [kg]/ height2 [m2]) was calculated. Using a steel measuring tape (Reynolds; Baofeng Inc, Ningbo, China), the waist circumference (WC) was measured to the nearest 0.1 cm; the measurement was taken on bare skin following a light expiration, with the participant standing. Measurement of Hand Grip Strength Handgrip strength (in kg) was measured by a handheld dynamometer based on strain gauge sensors (EH101; Xiangshan Inc, Guangdong, China). Both hands were tested with the participant seated, elbow flexed at a 110 angle, with the wrist in a neutral position, and the interphalangeal joint of the index finger at a 90 angle. Two readings were taken, and the highest value was used for the analysis. We conducted a preliminary study to evaluate the reliability of the handgrip strength test using the intraclass correlation coefficient (ICC). The result indicated that the test-retest reliability of the handgrip strength test was excellent (ICC ¼ 0.85, n ¼ 115). Classification of Obesity, Dynapenia, and Dynapenic-Obesity According to the World Health Organization Asian Criteria of Obesity,16 the participants represented either the nonobesity group (<25 kg/m2) or the obesity group (25 kg/m2). Muscle strength significantly differs by age and gender,17 so the handgrip strength values were regressed to a full cubic polynomial by age (age, age2, and age3) in the within-sex subgroups using a forward stepwise
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regression. The standardized residuals were retained to represent the age-adjusted values.18 The sex-specific tertiles of handgrip strength were calculated, and the participants in the lowest tertile of handgrip strength were grouped as dynapenic, whereas those in the second and the third tertiles were grouped as nondynapenic. The individuals were classified into the following 4 groups based on sex-specific age-adjusted handgrip strength and BMI: “dynapeniaalone,” “obesity-alone,” “dynapenic-obesity,” and “nondynapenia/ nonobesity.” Measurement of ADL and IADL Disability The functional status of each participant was evaluated by trained interviewers. The Katz Index of Independence in ADL,19 which included 6 items (bathing, dressing, toileting, transferring, continence, and feeding), was used to assess ADLs. The response to each item was “independent” (1 point) or “partly or completely dependent” (0 points). Six IADL items (public transportation, shopping, food preparation, housekeeping, responsibility for own medications, and handling finances) in the Older Americans Resources and Services (OARS) multidimensional functional assessment questionnaire 20 were used to assess IADLs. The response to each item was “without help” (2 points), “with some help” (1 point), and “completely unable to do” (0 points). The validity and reliability of the scales have been well established.20e22 The participants were defined as having an ADL or IADL disability when they reported a need for help from another person in performing at least one ADL questionnaire item (ADL disability) or one IADL questionnaire item (IADL disability). Assessment of Covariates The covariates in the analyses were age, gender, smoking status (current smoker, former smoker, and nonsmoker), alcohol intake status (current drinker, former drinker, and nondrinker), and education level (less than high school, high school, and more than high school). Physical activity was assessed by self-reporting. The participants were asked about the frequency and duration of physical activities of at least moderate intensity in the previous month. According to this information, the participants were classified into 3 groups (none, <30 minutes per day, 30 minutes per day). The following chronic conditions, which were potentially related to disability, were assessed by trained interviewers using a self-reported questionnaire: visual problems, hearing problems, arthritis, diabetes, lung disease (chronic bronchitis/emphysema or asthma), cardiovascular disease (hypertension, coronary heart disease, or chronic heart failure), central nervous system disease (stroke or dementia), and tumor. Statistical Analysis The statistical analyses were performed with the SPSS for Windows software package, version 11.5 (SPSS Inc, Chicago, IL). The continuous data are presented as unadjusted means SD, whereas the categorical variables are presented as percentage. The general linear models (GLMs) were applied to identify the difference in the continuous data among the 4 groups. Bonferroni post hoc analyses were performed to identify the group differences. Logistic regression models were applied to identify the differences for the dichotomized variables. All the regressions were adjusted for age, gender, alcohol intake status, smoking status, physical activity levels (min/d), and the chronic conditions mentioned previously. Because BMI and WC were highly correlated (Spearman correlation coefficient: 0.62), we further adjusted WC in Model 2. All P values were 2-sided, and significance was accepted at P less than .05.
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Results In total, 616 participants were included in the analyses, whereas 271 participants had missing data for handgrip strength or WC and were excluded from our analyses. The individuals selected for this study were similar in age (70.7 6.8 vs 69.8 7.2 years), gender (58.4% vs 56.1% women), and the prevalence of obesity (23.5% vs 22.9%) and ADL (10.7% vs 10.2%) or IADL disability (15.9% vs 15.3%) compared with those who were excluded. All of the participants were Han Chinese. General Characteristics According to the Dynapenia and Obesity Status Table 1 shows the general characteristics of the participants according to their dynapenia and obesity status. There was no significant difference across the 4 groups with respect to age, gender, the percentage of current smokers or current drinkers, and the percentage of participants who did physical activity 30 minutes per day. The mean sum of the chronic conditions was significantly greater in the obesity-alone group (1.9) than in the dynapenia-alone group (1.4) or the nondynapenia/nonobesity group (1.5) (P < .01). No significant difference was found between the dynapenic-obesity group and the other 3 groups (P < .05). Because of the study design, the obesity-alone and dynapenic-obesity groups had greater BMI and WC than the other 2 groups for men or women (P < .01). The dynapenia-alone and dynapenic-obesity groups exhibited lower handgrip strength than the other 2 groups for both sexes (P < .01). As expected by study design, there was no significant difference in the BMI and WC between the obesity-alone and the dynapenic-obesity groups in both sexes (P < .05). Similarly, there was no significant difference in handgrip strength between the dynapenia-alone and the dynapenic-obesity groups in men or women (P < .05). ADL Disability According to Dynapenia and Obesity Status The prevalence of ADL disability was 21.1% in the dynapenicobesity group, 15.5% in the dynapenia-alone group, 13.1% in the obesity-alone group, and 11.9% in the nondynapenia/nonobesity group. After adjusting for the covariates, with comparison to the dynapenic-obesity group, the adjusted odds ratios (95% confidence interval) for ADL disability were 0.36 (0.13e0.73) in the nondynapenia/nonobesity group, 0.51 (0.20e0.78) in the dynapeniaalone group, and 0.40 (0.11e0.61) in the obesity-alone group. As illustrated in Table 2, disability according to each item of the Katz
Index of Independence in ADL was compared across the 4 groups. The dynapenic-obesity group had the highest proportion of disability in each item, whereas the nondynapenia/nonobesity group had the lowest proportion, although no significant differences were identified with respect to disability in feeding and disability in continence disability. With comparison to the dynapenic-obesity group, a significant lower prevalence of disability was found in the dynapenia-alone or the obesity-alone group with respect to bathing, dressing, transferring, and toileting; the differences were not significant across the 3 groups in feeding and continence.
IADL Disability According to Dynapenia and Obesity Status The prevalence of IADL disability was 28.9% in the dynapenicobesity group, 22.6% in the dynapenia-alone group, 19.6% in the obesity-alone group, and 12.9% in the nondynapenia/nonobesity group. After adjusting for the covariates, with comparison with the dynapenic-obesity group, the adjusted odds ratios for IADL disability were 0.55 (0.20e0.93) in the nondynapenia/nonobesity group, 0.82 (0.39e0.98) in the dynapenia-alone group, and 0.61 (0.30e0.91) in the obesity-alone group. As illustrated in Table 2, disability in each IADL item of the OARS multidimensional functional assessment questionnaire was compared across the 4 groups. The dynapenicobesity group had the highest proportion of disability in each item, whereas the nondynapenia/nonobesity group had the lowest proportion (exception: responsibility for own medications and handling finances). No significant differences were found between the dynapenic-obesity group and the nondynapenia/nonobesity group with respect to the participant’s responsibility for his or her own medications and handling finances. In comparison with the dynapenic-obesity group, a significantly lower prevalence of disability was found in the dynapenia-alone or the obesity-alone group with respect to public transportation, shopping, food preparation, and housekeeping.
Discussion To the best of our knowledge, this study is the first to address the effect of obesity, dynapenia, and their combination on ADL/IADL disability in older Chinese adults. Our study indicates that older adults with dynapenia alone, obesity alone, or dynapenic-obesity had a higher prevalence of ADL and IADL disability in comparison with those without these conditions. Older adults with dynapenic-obesity
Table 1 Characteristics of Groups According to Obesity and Dynapenia Status Nondynapenia and Nonobesity n ¼ 303 Age, y Female, % Body mass index, kg/m2 Waist circumference male, cm Waist circumference female, cm Handgrip strength male, kg Handgrip strength female, kg Current smoker, % Current drinker, % Physical activity 30 min/d, % Sum of chronic conditions, 0e8
70.8 57.8 21.7 80.2 76.6 33.5 21.4 15.8 13.5 62.0 1.5x
7.1
2.1*,y 6.6*,y 7.3*,y 5.7*,y,x 5.0y,x
Dynapenia Alone n ¼ 168 71.2 59.5 21.4 78.8 76.8 19.8 10.5 11.3 19.6 58.3 1.4*
7.0
2.6*,y 6.4*,y 8.7*,y 6.7*,z 4.2*,z
Obesity Alone n ¼ 107
Dynapenic-Obesity n ¼ 38
69.9 59.8 27.0 90.6 88.4 36.9 23.0 14.9 15.9 62.6 1.9z,x
69.2 55.3 27.4 92.0 89.5 21.2 13.2 5.2 15.8 57.9 1.7
5.9 2.1z,x 8.6z,x 10.4z,x 5.7y,z,x 5.6y,x
6.4
2.1z,x 5.0z,x 6.7z,x 6.9*,z 3.5*,z
Categorical variables are presented as prevalence, whereas continuous data are presented as unadjusted mean SD. For categorical variables, Logistic regression models were used to identify any group difference among the 4 groups. For continuous data, general linear models were used to identify difference among the 4 groups and Bonferroni post hoc analyses were used to identify any group difference. Significance was accepted at P < .05. *Significantly different from obesity alone. y Significantly different from dynapenic-obesity. z Significantly different from non-dynapenia and non-obesity. x Significantly different from dynapenia alone.
M. Yang et al. / JAMDA 15 (2014) 150.e11e150.e16
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Table 2 Activity of Daily Living/Instrumental Activity of Daily Living Disability According to Obesity and Dynapenia Status
ADL disability Prevalence, % Model 1 Model 2 Bathing* Prevalence, % Model 1 Model 2 Dressing* Prevalence, % Model 1 Model 2 Feeding* Prevalence, % Model 1 Model 2 Transferring* Prevalence, % Model 1 Model 2 Continence* Prevalence, % Model 1 Model 2 Toileting* Prevalence, % Model 1 Model 2 IADL disability Prevalence, % Model 1 Model 2 Public transportation* Prevalence, % Model 1 Model 2 Shopping* Prevalence, % Model 1 Model 2 Food preparation* Prevalence, % Model 1 Model 2 Housekeeping* Prevalence, % Model 1 Model 2 Responsibility for own medications* Prevalence, % Model 1 Model 2 Handling finances* Prevalence, % Model 1 Model 2
Nondynapenia/ Nonobesity n ¼ 303
Dynapenia Alone n ¼ 168
Obesity Alone n ¼ 107
Dynapenic-Obesity n ¼ 38
11.9 0.41 (0.15e0.87) 0.36 (0.13e0.73)
15.5 0.54 (0.14e0.85) 0.51 (0.20e0.78)
13.1 0.42 (0.12e0.66) 0.40 (0.11e0.61)
21.1 1 1
4.0 0.47 (0.13e0.72) 0.45 (0.19e0.73)
4.7 0.81 (0.58e0.91) 0.78 (0.56e0.98)
4.6 0.68 (0.41e0.92) 0.67 (0.36e0.98)
5.3 1 1
1.7 0.52 (0.13e0.78) 0.58 (0.15e0.84)
2.4 0.61 (0.25e0.88) 0.65 (0.30e0.93)
1.9 0.55 (0.14e0.87) 0.60 (0.22e0.82)
2.6 1 1
2.3 0.76 (0.04e4.89) 0.70 (0.01e3.02)
2.4 0.88 (0.06e7.84) 0.81 (0.03e4.98)
1.9 0.63 (0.25e8.11) 0.61 (0.08e9.45)
2.6 1 1
1.7 0.17 (0.08e0.68) 0.24 (0.12e0.72)
1.8 0.29 (0.02e0.53) 0.35 (0.09e0.57)
1.9 0.30 (0.04e0.58) 0.34 (0.05e0.62)
5.3 1 1
8.6 0.75 (0.20e2.18) 0.79 (0.18e2.58)
8.3 0.70 (0.18e2.21) 0.78 (0.17e2.57)
8.4 0.74 (0.18e2.32) 0.79 (0.20e2.45)
10.5 1 1
0.7 0.22 (0.08e0.75) 0.15 (0.06e0.51)
1.8 0.32 (0.10e0.52) 0.28 (0.15e0.48)
1.9 0.36 (0.12e0.54) 0.33 (0.17e0.67)
5.3 1 1
12.9 0.41 (0.17e0.88) 0.55 (0.20e0.93)
22.6 0.78 (0.42e0.90) 0.82 (0.39e0.98)
19.6 0.61 (0.31e0.88) 0.61 (0.30e0.91)
28.9 1 1
5.9 0.32 (0.11e0.68) 0.48 (0.08e0.72)
11.3 0.56 (0.22e0.87) 0.62 (0.13e0.92)
13.7 0.57 (0.18e0.86) 0.68 (0.32e0.90)
15.8 1 1
5.3 0.42 (0.08e0.61) 0.41 (0.12e0.65)
10.7 0.69 (0.24e0.86) 0.61 (0.11e0.88)
10.9 0.69 (0.15e0.91) 0.62 (0.18e0.88)
15.8 1 1
5.3 0.38 (0.09e0.65) 0.32 (0.11e0.68)
6.5 0.42 (0.15e0.66) 0.38 (0.13e0.57)
10.3 0.72 (0.23e0.93) 0.67 (0.13e0.88)
15.8 1 1
6.6 0.40 (0.12e0.82) 0.35 (0.11e0.89)
12.5 0.75 (0.43e0.91) 0.71 (0.40e0.93)
10.3 0.66 (0.22e0.82) 0.61 (0.30e0.88)
15.8 1 1
5.0 0.49 (0.21e2.69) 0.52 (0.19e2.35)
5.4 0.51 (0.11e3.34) 0.54 (0.08e2.87)
4.7 0.41 (0.08e1.36) 0.38 (0.07e1.32)
10.5 1 1
4.3 0.69 (0.36e1.38) 0.74 (0.23e1.52)
6.5 0.75 (0.23e2.97) 0.80 (0.31e3.12)
3.7 0.62 (0.28e1.11) 0.65 (0.23e1.08)
5.3 1 1
IADL, instrumental activity of daily living. Data are presented as prevalence (%) and odds ratio (95% confidence interval). Model 1: adjusted for age, gender, race, alcohol intake status, smoking status, physical activity, and 8 chronic conditions (visual problems, hearing problems, arthritis, diabetes, lung disease, cardiovascular disease, central nervous system disease, and tumor). Model 2: further adjusted for waist circumference on the basis of Model 1. *Disability was defined as “need for any help from another person.”
had a higher prevalence of ADL and IADL disability than those with dynapenia or obesity alone. Most of the current studies that examine the independent and additive effects of obesity and muscle on function or disability focus on sarcopenic-obesity rather than dynapenic-obesity.2,23e26 The results of these sarcopenic-obesity studies are not consistent with each other, and some,23,27 but not all, of the studies concluded that
sarcopenic-obesity was associated with a greater risk of functional impairment or disability than obesity alone. Only a small number of studies15,18,28 addressed the effects of dynapenic-obesity on disability, and all of them concerned mobility disability. All the dynapenicobesity studies15,18,28 concluded that dynapenic-obesity was associated with a greater risk of mobility disability than obesity alone. The disagreement between the sarcopenic-obesity and dynapenic-obesity
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studies may be explained by the hypothesis that muscle strength, instead of “simply muscle mass,” is a critical risk factor of physical disability. This hypothesis has been supported by a systematic review by Manini and Clark,13 but further evidence is needed to draw a strong conclusion. It is notable that the term “sarcopenia,” which was initially defined as the age-related loss of muscle mass,6 was recommended to be synonymous with the age-related loss of muscle strength and function in a recent statement of the European Working Group on Sarcopenia in Older People (EWGSOP).29 In that case, the newer definition of sarcopenia seems to include the term “dynapenia.” However, a global consensus on the definition of sarcopenia has not been achieved.13,14 We argue that loss of muscle strength and loss of muscle mass need to be defined independently. As suggested by Manini and Clark,13 the term “sarcopenia” should be used in its original context to describe the age-related loss of muscle mass, whereas the term “dynapenia” should be used to describe the agerelated loss of muscle strength. First, loss of muscle strength in older people is weakly associated with loss of muscle mass.11 In fact, the decline in muscle strength is much more rapid than the concomitant loss of muscle mass.11 Further, maintaining or gaining muscle mass could not prevent aging-related loss of muscle strength.30 Second, a systematic review of 16 studies found that muscle strength, instead of muscle mass, is the critical factor for determining disability and mortality in the elderly.13 Our study indicates that dynapenia alone and obesity alone were associated with ADL disability. The association between obesity and ADL disability has been supported by a large body of evidence.19,22,24,31,32 There are studies reporting the relationship between dynapenia (measured with hand grip strength) and ADLs. In a 7-year prospective cohort study, handgrip strength was found to be an independent predictor of ADL disability among older Mexican Americans.32 In addition, Davis et al33 indicated that strength and BMI were associated positively and negatively with ADL disability, respectively. Our finding is consistent with the Davis et al33 study, but we found that dynapenic-obesity has a more negative effect on ADL than dynapenia alone or obesity alone. Our study indicates that dynapenia alone, obesity alone, and dynapenic-obesity had negative effects on IADLs, and the effect of dynapenic-obesity was greater than that of the other 2 conditions. The association between obesity and IADLs has been supported by some studies.5,34 Dynapenia (measured by handgrip and quadriceps strength) was associated with physical disability in IADL and functional limitation in a recent cross-sectional study.35 To our knowledge, no study is examining the effect of dynapenic-obesity on IADL disability. Skeletal muscle is essential for movement and ADLs/IADLs. Theoretically, a certain minimum level of muscle strength is needed to perform specific daily tasks, such as walking, feeding, and toileting. It is difficult to define this minimum threshold level, because it varies significantly from person to person and may be influenced by many internal (eg, posture or body weight) or external (eg, with or without assistive devices) factors. Based on daily experience, more strength is essential to complete some daily activities (eg, housekeeping) than others (eg, feeding). The present study found no significant differences across the 4 groups in terms of feeding, continence, responsibility for own medications, and handling finances. The reason might be that the minimum level of muscle strength for these tasks is relatively lower than that for other tasks (eg, housekeeping and shopping). Although Manini and Clark13 suggested that handgrip strength should be used as a screening test for dynapenia, whereas knee extensor strength is an advanced test for defining dynapenia, no consensus has been reached. We used handgrip strength to measure
dynapenia in this study for 2 reasons. First, it has been shown that handgrip strength is a good indicator of whole body strength, whereas low hand grip strength is consistently associated with a greater likelihood of mortality, the development of mobility disability, and an increased risk of complications.36 There is evidence that handgrip strength provided risk estimates similar to those of quadriceps strength.37 Second, in comparison with knee extensor strength, handgrip strength is easier to measure and the device is significantly less expensive and affordable for developing countries, such as China. There is no consensus on the cut point of handgrip strength or knee extensor strength to define dynapenia. In our study, we calculated the age-adjusted and sex-specific tertiles of hand grip strength, and defined individuals in the lowest tertile as those with dynapenia. This method has been used in other studies,18,38 although it is arbitrary. There are several limitations to this study. First, a causal effect association could not be established because of the cross-sectional design. Second, approximately 30% of the individuals were excluded from the analyses because of missing data that might induce selection bias, although the gender and mean age were very similar between the included and excluded population. Third, comparisons with other studies are difficult because the definition and standardized measurement of dynapenia have not been established. In conclusion, dynapenia alone, obesity alone, and dynapenicobesity were associated with an increased risk of ADL/IADL disability. Dynapenic-obesity was associated with a greater risk of ADL/IADL disability in comparison with dynapenia alone or obesity alone. Reference 1. Samper-Ternent R, Al Snih S. Obesity in older adults: Epidemiology and implications for disability and disease. Rev Clin Gerontol 2012;22:10e34. 2. Woo J, Leung J, Kwok T. BMI, body composition, and physical functioning in older adults. Obesity (Silver Spring) 2007;15:1886e1894. 3. Chen H, Guo X. Obesity and functional disability in elderly Americans. J Am Geriatr Soc 2008;56:689e694. 4. Al Snih S, Ottenbacher KJ, Markides KS, et al. The effect of obesity on disability vs mortality in older Americans. Arch Intern Med 2007;167:774e780. 5. Wee CC, Huskey KW, Ngo LH, et al. Obesity, race, and risk for death or functional decline among medicare beneficiaries: A cohort study. Ann Intern Med 2011;154:645e655. 6. Rosenberg I. Summary comments. Am J Clin Nutr 1989;50:1231e1233. 7. Janssen I, Heymsfield SB, Ross R. Low relative skeletal muscle mass (sarcopenia) in older persons is associated with functional impairment and physical disability. J Am Geriatr Soc 2002;50:889e896. 8. Visser M, Harris TB, Langlois J, et al. Body fat and skeletal muscle mass in relation to physical disability in very old men and women of the Framingham Heart Study. J Gerontol A Biol Sci Med Sci 1998;53:M214eM221. 9. Visser M, Langlois J, Guralnik JM, et al. High body fatness, but not low fat-free mass, predicts disability in older men and women: The cardiovascular health study. Am J Clin Nutr 1998;68:584e590. 10. Delmonico MJ, Harris TB, Lee JS, et al. Alternative definitions of sarcopenia, lower extremity performance, and functional impairment with aging in older men and women. J Am Geriatr Soc 2007;55:769e774. 11. Mitchell WK, Williams J, Atherton P, et al. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Front Physiol 2012;3:260. 12. Hughes VA, Frontera WR, Wood M, et al. Longitudinal muscle strength changes in older adults: Influence of muscle mass, physical activity, and health. J Gerontol A Biol Sci Med Sci 2001;56:B209eB217. 13. Manini TM, Clark BC. Dynapenia and aging: An update. J Gerontol A Biol Sci Med Sci 2012;67:28e40. 14. Clark BC, Manini TM. Sarcopenia ¼/¼ dynapenia. J Gerontol A Biol Sci Med Sci 2008;63:829e834. 15. Stenholm S, Alley D, Bandinelli S, et al. The effect of obesity combined with low muscle strength on decline in mobility in older persons: Results from the InCHIANTI Study. Int J Obes (Lond) 2009;33:635e644. 16. WHO, IASO, and IOTF. The Asia-Pacific Perspective: Redefining Obesity and its Treatment. Sydney: Health Communications Australia Pty Limited; 2000, p. 18. 17. Kallman DA, Plato CC, Tobin JD. The role of muscle loss in the age-related decline of grip strength: Cross-sectional and longitudinal perspectives. J Gerontol 1990;45:M82eM88. 18. Bouchard DR, Janssen I. Dynapenic-obesity and physical function in older adults. J Gerontol A Biol Sci Med Sci 2010;65:71e77.
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