Participants
An observational cross-sectional study was carried out with a total of 935 potential participants from the geriatric department of Zhejiang Hospital in China, and the baseline assessments were performed from October 2014 to September 2018. The inclusion criteria in this study were an age of 60 years or older and the ability to understand and communicate in Chinese. Participants with a history of Parkinson’s disease, Parkinson’s syndrome, dementia, MCI indicated by a score lower than 24 on the Mini-Mental State Examination (MMSE) or mobility disability [1] who were unable to ambulate with or without walking aids were excluded. Participants who had incomplete data used to diagnose MCR were also excluded. Data were collected by a trained geriatric physician and nurse via a computer-aided hospital-based comprehensive geriatric assessment.
Approval for this study was granted by the medical ethics committees of Zhejiang Hospital (2013-25), and written informed consent was obtained from each participant. This study has not been registered, and the manuscript was written according to the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) statement.
MCR diagnosis
Based on the MCI operational definition [32,33], Verghese and colleagues proposed the MCR concept [1]. MCR was diagnosed as both the presence of subjective cognitive complaints and slow gait in those without dementia or mobility disability [1]. Subjective cognitive complaints were determined by face-to-face interviews based on responses to one item on a 15-item geriatric depression scale (GDS-15) [34]. The standardized question “Do you feel you have more problems with memory than most?” was asked by a well-trained nurse. A positive response “yes” on this question indicated a subjective cognitive complaint. Gait speed (m/s) was calculated by the four-metre usual gait speed test. The participants completed the test twice while starting from an inactive standing position (walking aids or cane allowed), and the shortest time was recorded. Slow gait was defined as gait speed one standard deviation below the age- and sex-specific means [1]. The cut-off values of slow gait in this study were: males 60-74 years ≤0.91 m/s, males ≥75 years ≤0.69 m/s, females 60-74 years ≤0.80 m/s, females ≥75 years ≤0.66 m/s.
According to the MCR criteria, all participants were classified to 4 groups: 1) the MCR group; 2) the subjective cognitive complaints only group; 3) the slow gait only group; and 4) the healthy control group.
Frailty assessment
Based on the Canadian study on Health and Aging, frailty was assessed by the Clinical Frailty Scale (CFS), which was scored from 1 (very fit) to 7 (severely frail) [35,36]. The evaluator recorded the level of frailty using their clinical judgement based on available clinical information. In this study, a CFS score greater than four indicated frailty [37].
The CFS was assessed by a well-trained assessor who was qualified in geriatric comprehensive assessment. There are three qualified members in our team, and they had evaluated a total of 1122 cases. The CFS assessor was blinded to the MCR assessor results.
Other covariates
Demographic data including age, sex, educational level, marital status, cigarette smoking and alcohol drinking use were obtained. Smoking status was categorized into non-smokers, former smokers and current smokers on the basis of self-reported amount and length of cigarette smoking. Current smokers were those who smoked regularly at least once a day or more for more than half a year, and former smokers were those who used to smoke but stopped smoking at least half a year prior to the study [38]. Alcohol drinking status was classified into non-drinkers, former drinkers and current drinkers based on the self-reported amount and duration of alcoholic beverages. Current drinkers were those who drank at least once a week for more than six months, and former drinkers were defined those who stopped drinking at least six months prior to the start of the study [38]. Body mass index (BMI) was calculated with height and weight. Physician-diagnosed chronic medical diseases were recorded according to the International Classification of Diseases, Tenth Revision (ICD-10) codes. Diabetes mellitus, cerebrovascular diseases, hypertension and coronary artery disease were included in this study. Comorbidities were defined as the coexistence of five kinds of chronic diseases or more. Participants who took five or more oral prescription medications were considered to the polypharmacy criteria [39]. A history of falls in the past year was also recorded. A fall was defined as a sudden, involuntary, unintentional change of position resulting in rest on the ground or another lower plane [40]. Dominant hand grip strength was measured three times using a hand dynamometer. The maximum of the three measurements was recorded for the final analysis. Depression symptoms were evaluated using the GDS-15 [34] and cognitive function was assessed using the MMSE [41].
Statistical analysis
Normal distributed continuous variables are presented as the means± standard deviations (SDs), and categorical variables are expressed as numbers (percentages). The unpaired t-test (for normally distributed continuous data) and the chi-square test (for categorical data) were used to identify the significant differences between the male and female groups. One-way ANOVA (for normally distributed continuous data) and the chi-square test (for categorical data) were used to identify the significant differences among the control, subjective cognitive complaints only, slow gait only and MCR groups. Furthermore, the association of MCR with frailty was analysed using multivariate logistic regression models and expressed in odds ratios (ORs) and 95% confidence intervals (CIs). Multivariate logistic regression was conducted with 3 models. Model 1 was not adjusted covariates; Model 2 was adjusted for age, sex and education; and Model 3 was adjusted for marital status, BMI, comorbidities, polypharmacy, fall history, grip strength, depressive symptoms and MMSE scores, in addition to the variables adjusted in Model 2. The data were analysed by using SPSS 18.0 software (SPSS, Chicago, IL, USA). All significance tests were two-tailed, and statistical significance was indicated by P<0.05.