Disability prevalence increases with advanced age [
There is a big gap between the scale of the problem and the quantity and quality of available information. The first population-based report from China was published 16 years ago [
In this study, with large population-based data from Shanghai (the biggest city in China) and Singapore (a city country in Southeast Asia, with majority of the residents being descendents of immigrants from South China), we aimed to examine the independent contributions of physical and cognitive health to disability in Chinese older adults and explore the potential influences of environment.
Participants of the present study were identified from two big population-based studies: the Shanghai Survey of Alzheimer's Disease and Dementia (SSADD) and the Singapore Longitudinal Ageing Study (SLAS). The SSADD was conducted in 1987 based on a probability sample of 5055 community-dwelling Chinese older adults from Jing’an district of Shanghai city. The SLAS was conducted among a total population sample of 2808 older adults from South East Region of Singapore. Baseline assessments of the SLAS were completed from September 2003 to December 2005. Details of the SSADD [
For the present analysis, we selected 4639 participants from the SSADD sample and 2397 participants from the SLAS cohort. All participants had complete data on demographic information, physical health, and cognitive function and obtained a Mini-Mental State Examination (MMSE) total score of at least 21 points.
Face-to-face interviews were conducted by psychiatrists/psychiatric nurses (in Shanghai) or trained research nurses (in Singapore), and data were collected for a wide range of variables. For the present analysis, we extracted the following variables from the databases: age, sex, functional status, chronic diseases, self-rated health status, and MMSE total score.
Functional status was assessed by the participant’s level of dependency in performing 8 Activities of Daily Living (ADL): eating, grooming, dressing, transferring, walking, toileting, bathing, and climbing stairs. Disability was defined as needing help in at least one ADL.
A list of 32 medical conditions was included in the SSADD interview schedule. The participants were asked “Do you have or not have any of the following illnesses or conditions at the present time?" In the SLAS, a list of 14 medical conditions was covered in the interview. The participants were asked “Do you have a history of this medical problem?” Medical conditions that were not included in the list were recorded under “any other problems.” We selected ten chronic diseases on which data were available from both samples: hypertension, diabetes, heart diseases (in Singapore: defined as any of heart attack, heart failure, or atrial fibrillation), stroke (in Shanghai: effects of stroke), kidney disorder (in Singapore: kidney failure), chronic obstructive lung disease (in Shanghai: emphysema/bronchitis), asthma, arthritis (in Shanghai: arthritis or rheumatism), mental illness, and cancer (in Singapore, identified from “any other problems”). In statistical analysis, the number of chronic diseases was used as an objective measure of physical health.
In Singapore, self-rated health status was assessed using a single question: “In general, would you say your health is: excellent, very good, good, fair, or poor?” In Shanghai, the same question was asked but there were four choices: excellent, good, fair, poor. We grouped “excellent” and “very good” together and created a new variable “self-rated health status”: 1 = excellent or very good, 2 = good, 3 = fair, and 4 = poor. This was used as a continuous variable in multivariate analyses (score ranged from 1 to 4, with higher value representing poorer health status).
Cognitive function was assessed by Mini-Mental State Examination (MMSE) test [
Chi-square test (for dichotomous variables) or independent sample
Table
Characteristics of the participants.
Shanghai ( | Singapore ( | ||
---|---|---|---|
Age (years) | 68.3 (7.8) | 65.6 (7.2) | <0.001 |
Range (years) | 55–93 | 55–97 | |
55–64 | 1167 (31.6%) | 1158 (48.3%) | <0.001 |
65–74 | 2074 (44.7%) | 938 (39.1%) | |
75+ | 1098 (23.7%) | 301 (12.6%) | |
Female | 2510 (54.1%) | 1495 (62.4%) | <0.001 |
Number of chronic diseases | 1.29 (1.18) | 1.16 (1.09) | <0.001 |
Self-rated health status* | 2.59 (0.77) | 2.38 (0.65) | <0.001 |
Excellent or very good | 164 (3.5%) | 145 (6.0%) | <0.001 |
Good | 2241 (48.3%) | 1257 (52.4%) | |
Fair | 1569 (33.8%) | 925 (38.6%) | |
Poor | 665 (14.3%) | 70 (2.9%) | |
MMSE total score | 26.6 (2.8) | 27.6 (2.2) | <0.001 |
Functional disability† (whole sample) | 233 (5.0%) | 43 (1.8%) | <0.001 |
Within age group 55–64 | 15 (1.0%) | 14 (1.2%) | 0.65 |
Within age group 65–74 | 82 (4.0%) | 18 (1.9%) | 0.004 |
Within age group: 75+ | 136 (12.4%) | 11 (3.7%) | <0.001 |
Disability in any of the ADL items | |||
Eating | 11 (0.2%) | 5 (0.2%) | 0.81 |
Grooming | 29 (0.6%) | 8 (0.3%) | 0.11 |
Dressing | 38 (0.8%) | 11 (0.5%) | 0.09 |
Transferring | 37 (0.8%) | 9 (0.4%) | 0.04 |
Walking | 43 (0.9%) | 14 (0.6%) | 0.13 |
Toileting | 38 (0.8%) | 17 (0.7%) | 0.62 |
Bathing | 162 (3.5%) | 9 (0.4%) | <0.001 |
Climbing stairs | 144 (3.1%) | 28 (1.2%) | <0.001 |
*Range from 1 (excellent or very good) to 4 (poor), with higher value representing poorer health.
†Defined as needing assistance in performing at least one of the eight Activities of Daily Living.
Data are mean (SD) or number (%).
MMSE: Mini-Mental State Examination.
In multiple logistic model based on the combined sample, number of chronic diseases, self-rated health status, MMSE total score, and environment were significantly associated with disability (Table
The independent contributions of health variables and environment to disability*: combined analysis.
Variable | Logistic regression | |
OR (95% CI) | ||
Number of chronic diseases | 1.35 (1.22–1.50) | <0.001 |
Self-rated health status† | 2.85 (2.36–3.43) | <0.001 |
MMSE total score | 0.89 (0.85–0.94) | <0.001 |
Environment | ||
Shanghai 1987 | 1.0 | |
Singapore 2003 | 0.68 (0.48–0.96) | 0.03 |
*Defined as needing assistance in performing at least one of the eight Activities of Daily Living.
†Range from 1 (excellent or very good) to 4 (poor), with higher value representing poorer health.
MMSE: Mini-Mental State Examination.
Variables in the model: age, gender, number of diseases, self-rated health status, MMSE total score, and environment (study sample).
Results from stratified analysis showed that the strength of associations between health variables and disability differed between the two samples (Table
Association between health factors and disability in Shanghai and Singapore: stratified analysis.
Variable | Shanghai ( | Singapore ( |
OR (95% CI) | OR (95% CI) | |
Number of chronic diseases | 1.36 (1.22–1.52) | 1.54 (1.21–1.97) |
Self rated overall health | 3.13 (2.55–3.85) | 1.73 (1.07–2.81) |
MMSE total score | 0.91 (0.86–0.96) | 0.83 (0.73–0.94) |
Variables in the model: age, gender, number of chronic diseases, self-rated health status, and MMSE total score.
Based on data from two population-based studies, we found that the number of chronic diseases, self-rated health status, cognitive function, and unmeasured environment factors represented by study sample were significantly associated with functional disability among Chinese older adults.
The contributions of physical health [
We found that environment was significantly associated with disability. Participants in the Singapore sample were 32% less likely to have disability compared with participants in the Shanghai sample. Participants from both studies were Chinese older adults living in big city, and a number of important covariates were adjusted in multiple regression models. It is less likely that the observed difference was caused by unmeasured factors at individual level.
We did not collect data on objective indicators of environmental factors. However, a careful examination of the two most difficult ADL tasks (bathing and climbing stairs) provided us with plausible explanations. In 1987, most families in Shanghai had no bathroom and shower, and bathing was considered as a complicated task [
Our study provided fresh evidence on the role of environmental factors in disablement process [
Strengths of our study include concurrent measuring of various health factors and simultaneous inclusion of those factors in multivariate model. This made a cross-comparison of the strength of independent associations possible. However, no causal relationship could be drawn given cross-sectional nature of the study design.
In conclusion, physical health and cognitive function were significantly associated with disability among Chinese older adults living in Asian metropolises. The association could be influenced by environment. A comprehensive approach should be adopted in disability prevention.
There are neither financial nor dual commitments that represent potential conflict of interests.
All the authors contributed substantially to the design, analysis and interpretation of the data and participated in drafting or revising the paper.
The Singapore Longitudinal Ageing Study was supported by Grants (no. 03/1/21/17/214 and no. 08/1/21/19/567) from the Biomedical Research Council, Agency for Science, Technology and Research in Singapore. The Shanghai Survey of Alzheimer's Disease and Dementia was supported by Shanghai Health Bureau, the Alzheimer’s Disease Research Center (AG05131) and the Riford Chair in Alzheimer Disease Research at the University of California, San Diego, and the Nation Institute of Mental Health (MH36408) in Washington, DC.