Study population
The Kawasaki Aging and Wellbeing Project (KAWP) is a longitudinal cohort study of older adults aged between 85 and 89 with no physical disability at baseline. The prime aim of the KAWP is to explore trajectories of functional decline, frailty, and cognitive impairment, and to identify genetic, biological, behavioral, and socioenvironmental factors that delay or modify this deteriorating process at an advanced age. The inclusion criteria of KAWP are: 1) being a resident of Kawasaki city, a city with a population of 1.5 million, located in the Greater Tokyo Area and aged between 85 and 89; 2) having no limitations in the basic activities of daily living (ADL); and 3) being able to visit the study site, the Kawasaki Municipal Hospitals independently.
Using the basic registration of residents and the long-term care insurance database, a total of 12,906 were screened as potential participants. Among them, we mailed an invitation letter for this study to 9,978 individuals, and 1,464 eligible residents responded to express their willingness to participate in the study. Between March 2017 and December 2018, a total of 1,026 independent seniors were enrolled in the KAWP and a comprehensive baseline assessment, including assessment of physical, mental, and cognitive function as well as social participation was conducted (Figure 1). Thereafter, the participants were scheduled for telephonic surveys every 6 months to monitor their vital status, any incidental disabilities, falls and fractures, and hospitalizations until December 2024 or until they dropped out.
In this study, we selected 546 people who were scheduled for follow-up telephonic surveys between May 25, 2020, the day the state of emergency was lifted, and the end of August 2020. Written informed consent to participate in the KAWP was obtained from all participants. The KAWP was approved by the ethics committee of the Keio University School of Medicine (ID: 20160297) and was registered in the University Hospital Medical Information Network Clinical Trial Registry as an observational study (ID: UMIN000026053).
Measurements
COVID-19 questionnaire
The COVID-19-related telephonic interviews were conducted by two trained interviewers between May 25 and August 31, 2020 using a structured questionnaire (Additional file 1) in addition to the usual 6-month follow-up telephonic survey. The questionnaire consisted of 11 closed-ended questions and one open-ended question regarding perceived changes in basic lifestyle, physical activity, conversation time, and precautious behaviors during the state of emergency. Each interview was completed in approximately 10–20 minutes.
Baseline characteristics
Sociodemographic and health data were obtained from the KAWP baseline survey conducted between March 2017 and December 2018 (on average 2.2 years before the telephonic survey). All participants were invited to visit one of three Kawasaki Municipal Hospitals (Kawasaki, Ida, or Tama) and were interviewed and examined using a study protocol that was harmonized with the Tokyo Oldest Old Survey on Total Health and Japan Semi-supercentenarian Study, both of which are managed by the Center for Supercentenarian Medical Research, Keio University School of Medicine.7, 8 Participants were asked to fill out a pre-mailed questionnaire including education (high school and higher education or not), living situation, marital status, current alcohol use, smoking status, and self-rated health. They were checked for consistency by interviewers at the time of the baseline survey.
The medical interview was conducted by trained physicians, and the number of chronic conditions was counted based on past and present medical history of 18 diseases: cerebrovascular disease, cardiac disease, hypertension, diabetes, dyslipidemia, respiratory disease, gastrointestinal disease, renal disease, prostate disease, thyroid disease, Parkinson's disease, connective tissue disease, eye disease, osteoporosis, arthritis, hyperuricemia, malignancy, and dementia. Body weight and height were measured while wearing light clothes and standing upright. Instrumental activities of daily living (IADL) were assessed using the Lawton scale (0–5 points),9 cognitive functions were evaluated according to the Mini-Mental State Examination (MMSE; 0–30 point) 10 and depression was assessed using the Geriatric Depression Scale (GDS-15).11 Self-rated health is scored by a Likert-type scale ranging from 1 (very poor) to 5 (very good). Physical activity in the past one year was assessed using the modified Zutphen Physical Activity Questionnaire.12 The questionnaire determined the frequency and duration of walking, cycling, and other leisure-time physical activities. Physical Activity Index (PAI) was then calculated by multiplying the activity intensity (compendium-coded, metabolic equivalents METs) with duration (hours) and frequency (times per week). The questionnaire was validated with a tri-axial accelerometer and physical functions in the very old adults.12 Upper tertile of PAI was regarded as engagement in physical activity. Hearing and visual acuity were rated according to self-reported categories. Those who responded “need a loud voice or speak in his/her ears” or “cannot hear at all” were judged as having a hearing impairment. Those who rated “poor” and “very poor” for eyesight were regarded as visually impaired. Self-reported community interaction was evaluated according to the following question: “How often do you meet or talk to people in the community you associate with (including phone and email exchanges)?” Here, a community is defined as an area that is about a 10-minute walk away.
Statistical analysis
Baseline characteristics are expressed as medians and interquartile ranges (IQR); categorical variables are shown as numbers and proportions. Correlation between numerical variables assessed at baseline survey was calculated with Spearman’s correlation coefficients. Crude odds ratio (OR) and 95% confident interval (CI) were calculated for behavioral factors such as decreased physical activity and conversation time and washing hands more. Multivariable logistic regression analysis was performed to examine the independent association between behavioral factors and baseline characteristics, in which all variables were mutually adjusted in the models. All analyses were performed using SPSS Statistics ver. 24.0 software (Armonk, NY: IBM Corp.), and results were considered statistically significant at a P -value of <0.05, and two-sided tests were applied.