Study design
This study conducted a secondary analysis of the 2017 data from the National Survey of Older Koreans (NSOK) to investigate the factors influencing the stages of frailty in older adults living in community, focusing on objective and subjective social isolation.
Data and ethical considerations
This study analyzed the 2017 data from the NSOK conducted by the Ministry of Health and Welfare [28]. The NSOK has been conducted every three years since 2008 to study older adults aged ≥65 years in South Korea. In 2017, 10,299 older adults aged ≥65 years in 934 regions were studied. The survey uses nationally representative samples of non-institutionalized Korean older adults aged 65 or over who lived in the community. The data can be obtained from the public data portal (data.go.kr) after the institution’s application and subsequent approval [28]. This study was conducted with an exemption of Institutional Review Board (IRB) approval at the author’s university (IRB No: 1044396-202102-HR-030-01). The data of 258 individuals with missing values among the 10,299 in the original data set were excluded, and 10,041 older adults were included in the analysis.
Measurements
Frailty
Frailty was measured using the FRAIL Scale with the following five domains: fatigue, resistance, ambulation, illness, and loss of weight [15], which has been validated for use in older Koreans [13]. In this study, the five domains of the FRAIL Scale were assessed according to the following criteria. 1) Fatigue: For the question, “Have you experienced a significantly reduced level of activity or drive recently?”, a “No” response was given a score of 0, and a “Yes” response was given a score of 1. 2) Resistance: For the question, “How difficult is it for you to climb ten stairs without rest?”, a response of “Not difficult at all” or “A little difficult” was given a score of 0 (not difficult), and a response of “Very difficult” or “Too difficult to do” was given a score of 1 (difficult). 3) Ambulation: For the question, “How difficult is it for you to complete one round of a walk in a schoolyard (400 m)?”, a response of “Not difficult at all” or “A little difficult” was given a score of 0 (not difficult), and a response of “Very difficult” or “Too difficult to do” was given a score of 1 (difficult). 4) Illness: If a participant had three or fewer diseases diagnosed by a health care professional (e.g., hypertension, diabetes, cancer, chronic bronchitis or pulmonary emphysema, angina or cardiac infarction, other heart conditions, asthma, arthritis, stroke [paralysis or cerebral infarction], and chronic renal disease), a score of 0 was given. If a participant had been diagnosed with four or more diseases, a score of 1 was given. 5) Loss of weight: It was defined as loss of weight when an individual had a loss or gain of 5 kg without weight control over the previous six months and is underweight with body mass index (BMI) of less than 18.5 kg/m2. In this case, a score of 1 was given. A score of 0 was given to all other cases. The total score of the above five domains was calculated. A total score of ≥3 indicates frail, 1–2 indicates pre-frail, and 0 indicates a robust health state [29].
Social isolation
Objective social isolation was measured by combining the frequency of contact with family and contact with friends, neighbors, and acquaintances [24], based on two questions: “How often do you communicate (via phone, mobile message, email, letter, etc.) with a family member living elsewhere?” and “How often do you communicate with a friend, neighbor, or acquaintance?”. The scoring was based on a seven-point scale (1 = “never”, 2 = “1–2 times a year”, 3 = “1–2 times every three months”, 4 = “1–2 times a month”, 5 = “at least once a week”, 6 = “2–3 times a week”, 7 = “nearly every day [more than four times a week]”) to categorize the subjects into the following two groups: not isolated (nearly every day [more than four times a week], 2–3 times a week, at least once a week, or 1–2 times a month) and isolated (1–2 times every three months, 1–2 times a year, or never). After regrouping, objective social isolation was categorized into the following four groups: 1) not isolated from family or friends, 2) isolated from family only, 3) isolated from friends only, and 4) isolated from both family and friends. Subjective social isolation was measured based on the question: “With how many family members (parents and siblings), relatives, friends, neighbors, and acquaintances are you intimately close (to share all your thoughts and feelings)?”.
Sociodemographic and health-related characteristics
The sociodemographic factors were measured using self-reported questions: gender, age, education level, annual household income, and living arrangement. Age was divided into a 65–74 years group and a ≥75 years group. Education level was reclassified into no formal education, elementary school graduation, and more than middle school graduation. Annual income was divided into quartiles: lowest 25%, 26–50%, 51–75%, and highest 25%. Living arrangement was divided into living alone and living with others. Health-related factors including Activities of Daily Living (ADL) and Instrumental Activities of Daily Living (IADL) dependency, cognitive function, vision and hearing sensory, and exercise were assessed. ADL dependency was measured based on the seven items of the Korean Activities of Daily Living (K-ADL). IADL dependency was measured based on the ten items of the Korean Instrumental Activities of Daily Living (K-IDL). Dependency was assigned if at least one item indicated a need for assistance [30]. Cognitive function was measured using the Mini-Mental State Examination for Dementia Screening tool developed by Kim et al. [31]. This tool consists of 19 items, and the total score is calculated from the sum of all items. Normal and cognitive decline are classified according to the norm score based on age, sex, and education level. The validity and reliability have been verified in previous studies, and the reliability of the tool was Cronbach’s alpha = .81 [31].
Visual and auditory sensory functions were assessed using questions of discomfort in daily life regardless of the use of assistants such as glasses and hearing aids. The questions were about discomfort while watching television, reading the newspaper, and talking on the phone or with someone next to them. The response of “Not uncomfortable” was categorized as “good” and “Uncomfortable or Very uncomfortable” as “not good”. We assessed exercise using two questions: "How many days per week do you exercise?" and "How many minutes do you exercise per day?". Individuals who exercised more than 30 minutes a day and more than 3 times a week were classified as “regular exercise”.
Statistical analysis
SPSS 23.0 was used for all statistical analyses. To analyze characteristics of social isolation and stages of frailty and the correlation between social isolation and the stages of frailty, χ2 test, t-test, one-way ANOVA with Scheffe test, and descriptive statistics were used (Aim 1). Two multiple logistic regression analyses were performed to identify the factors influencing the frailty stages, one with the “robust” group as the reference and the other with the “pre-frail” group as the reference (Aim 2). For these analyses, the model was run with five sociodemographic characteristics (gender, age, educational level, annual household income, and living arrangement), six health-related characteristics (ADL dependency, IADL dependency, cognitive decline, vision sensory, hearing sensory, and regular exercise), and two factors of social isolation (objective social isolation and subjective social isolation) in association with the stages of frailty. Odds ratios (ORs) indicated the likelihood of membership in the “pre-frail” group (relative to the “robust” group) and the “frail” group (relative to the “pre-frail” group).