The present single-center, cross-sectional study used the baseline data of prospective cohort study Juntendo Sarcopenia Registration of Exploring for Predictors and Prognosis in the elderly in Tokyo (JUSTICE-TOKYO) (7), in accordance with the guidelines contained in the STROBE Checklist (8).

The JUSTICE-TOKYO study is a prospective, observational cohort study of consecutive outpatients aged ≥65 years attending Juntendo Tokyo Koto Geriatric Medical Center, Tokyo, Japan. The study enrolled 1,042 patients between November 2020 and November 2021 and will be completed in 2025. The participants will be followed up annually for 4 years after enrollment to determine survival, incidence of falls, number of hospitalizations and skeletal muscle mass. At enrollment, baseline data including patient profile [age, body mass index (BMI), Brinkman Index (BI), drinking habits, sex, history of falls, daycare use, social frailty, phase angle (PhA) and QOL], comorbidities, questionnaires [Mini-Mental State Examination (MMSE), Geriatric Depression Scale 15 (GDS-15), Abdominal symptom-related QOL (Izumo scale) scores, constipation scoring system (CSS), chronic obstructive pulmonary disease (COPD) assessment test (CAT)] (9-13), physical and skeletal muscle mass, physiological function test and nutritional assessment data were collected and entered prospectively into the Research Electronic Data Capture system, which provides web-based software for the creation of secure online forms (14).

Patients were excluded for the following reasons: i) Inability to walk independently because of severe osteoarthritis or neuromuscular disease, ii) immobility, iii) delirium tremens at presentation, iv) history of gastrointestinal, renal, acute cerebrovascular, coronary, hepatic and respiratory events, v) inability to be interviewed by questionnaire and vi) predicted life expectancy <1 year because of malignant disease.

Inclusion was limited to patients whose information at registration included all of the following:

i) Age, body mass index (BMI), Brinkman Index (BI) (15), drinking habits (0, rarely drinks alcohol; 1, drinks alcohol 1-4 days/week and 2, drinks alcohol 5-7 days/week), sex, history of falls and daycare use, social frailty, phase angle (PhA) and quality of life assessed by EuroQol Visual Analogue Scale (EQ-VAS) (16-18). Social frailty was assessed using questions regarding living alone, going out less frequently compared with the prior year, visiting friends sometimes, feeling helpful to friends or family and talking with someone every day. Resistances to a multi-frequency alternating current applied to the trunk, arms and legs were measured to determine body composition and impedance characteristics, including capacitive reactance and PhA, were analyzed by an MC-780A body composition analyzer (TANITA Corporation). PhA was calculated as follows: [- arc tangent (reactance/resistance) x180˚/π] (19). PhA represents resistance of the cell membrane, the volume of somatic cells and the distribution of intra- and extracellular fluid; higher PhA generally indicates good cell health, while lower value of PhA reflects structural damage to the cell membrane and decreased cell density, indicating poor cell function (20). Dual-energy X-ray Absorptiometry) standard method for measuring an appendicular skeletal muscle mass in sarcopenia was used (21). PhA cannot be measured by the DXA method but can be measured by the BIA (Bioelectrical Impedance Analysis) method to investigate whether PhA is associated with sarcopenia in older outpatients (22). QOL was evaluated by EQ-VAS (0=worst health, 100=perfect health), commonly used in primary care. Anthropocentric measures, physiological performance test, walking speed, and various questionnaires [(Izumo scale), constipation scoring system (CSS), chronic obstructive pulmonary disease (COPD) assessment test (CAT), Dietary Variety Score (DVS)] (11-13,23) were conducted by nurses and nutritionists.

ii) Comorbidities [history of atrial fibrillation, cerebral infarction/hemorrhage, diabetes mellitus (DM), hospitalization for heart failure, hypertension, interstitial pneumonia, malignant disease, myocardial infarction and osteoporosis]. The age-adjusted Charlson comorbidity index was calculated for each patient (24,25). T-score and young adult mean (YAM) % were measured by DXA of the total hip and lumbar spine (L2-L4). Prodigy Advance scanner (GE Healthcare) was used to perform DXA. Osteoporosis was diagnosed in accordance with Japanese Society for Bone and Mineral Research criteria (26).

iii) Use of therapeutic agents (statins, acid secretion suppressants, laxatives, steroids, analgesics, antidementia drugs, antipsychotic drugs) and number of oral medicines. Data on medications and number of oral medicines were obtained by pharmacists from patient health notebooks.

iv) Neuropsychological examinations [Geriatric Depression Scale 15 (GDS-15) and Mini-Mental State Examination (MMSE)] (9,10) were performed by psychiatrists.

v) Abdominal symptom-related QOL (Izumo scale) scores (constipation-, diarrhea-, fullness-, reflux- and upper abdominal pain-related QOL) (11). QOL impairment was ranked from 0 (no impairment) to 15 (symptomatic).

vi) Severity of constipation was rated using the constipation scoring system (CSS) (12), comprised of eight items: Abdominal pain, assistance for evacuation, duration of constipation, frequency of bowel movements, incomplete evacuation, length of time/attempt, number of unsuccessful attempts at evacuation/24 h and painful evacuation. The overall CSS score, which is the sum of the item scores, ranged from 0 to 30, with a higher score signifying constipation symptoms were worse. Gastroenterologists performed the constipation severity assessments using CSS and Izumo scales.

vii) Pulmonary function data [arterial oxygen saturation (SpO₂), chronic obstructive pulmonary disease (COPD) assessment test (CAT)] results, restricted and obstructive ventilatory impairment) (13,27). The 8-item CAT was used to assess the impact of COPD on health status. CAT score ≥10 indicated a high symptomatic level. Pulmonary function tests including vital capacity (VC), forced VC (FVC) and forced expiratory volume in 1 sec (FEV1) were performed on a Minato System 21 (Minato Medical Science Co., Ltd.). The pulmonary function tests, CAT and eating assessment test 10 (EAT10) (28) were evaluated by a respiratory physician.

viii) Nutritional status [hypozincemia, controlling nutritional status (CONUT) score, DVS)] (23,29). Hypozincemia was defined as requiring treatment with zinc acetate hydrate (Novelzin^® Tablets, Nobelpharma K.K.) or serum zinc levels <80 µg/dl. Zinc is a trace element essential for life. Appetite loss (30), depression (31), and taste abnormality (32) are hypozincemia-associated symptoms and risk factors for hypoalimentation. CONUT score (0-12; calculated from serum albumin and total cholesterol levels and total lymphocyte count) (29) was used to measure objective nutritional status. Comprising 10 food-based components (23), DVS was calculated as follows. First, consumption frequencies during 1 week were determined for each of 10 food items (meat, fish/shellfish, eggs, milk, soybean products, green/yellow vegetables, potatoes, fruit, seaweed and fats/oils). Second, scores were assigned as follows: 1, eaten almost daily and 0, not eaten almost daily. Third, the item scores were summed and the total DVS was in the range 0 to 10, with higher scores indicating greater dietary variety.

ix) Oral function [Oral Frailty Index (OFI)-8 and EAT10] (28,33). Oral frailty was defined as OFI-8 score ≥4. The EAT10 tool was used to assess dysphagia severity. The data were collected within 3 months after registration.

Diagnostic algorithm recommended by AWGS 2019 Consensus was used to define (21). The handgrip strength was measured twice each with both hands using a handgrip dynamometer (Toei Light Co., Ltd.), and the larger value was noted as the maximum muscle strength. Low grip strength was defined as <28 for male and <18 kg for female patients, according to AWGS criteria. Gait speed, manually assessed using a stopwatch, was defined as slow when <1.0 m/sec according to AWGS criteria. Lean mass and regional fat were assessed from whole-body DXA scans (Prodigy Advance, GE Healthcare). Subjects were positioned for whole-body scans in accordance with the manufacturer's protocol. The whole-body fat mass and lean mass were divided into arms, legs and trunk. The appendicular lean mass was estimated as the sum of the lean mass of the upper and lower limbs. The appendicular skeletal muscle mass index (SMI) was calculated as the appendicular lean mass divided by the square of the height (34). A low appendicular skeletal muscle mass was defined as appendicular SMI <7.0 in male and <5.4 kg/m² in female patients.

Subjects were divided into sarcopenia and non-sarcopenia groups and risk factors for sarcopenia were compared by uni- and multivariate analyses. Quantitative data are expressed as mean ± standard deviation. In univariate analyses, χ² test was used for categorical variables and unpaired Student t tests were used for continuous variables. Independent variables with P<0.20 in the univariate analysis were included in multivariate logistic regression analysis. The odds ratio (OR) and 95% confidence interval (CI) were used to assess the strength of any associations. All statistical analyses were performed using the SPSS version 28 software (IBM Corporation). P<0.05 was considered to indicate a statistically significant difference.

The clinical characteristics are summarized in Table I. Participant recruitment flow diagram is shown in Fig. 1. Mean age-adjusted Charlson Comorbidity Index score was 5.5±1.4. Sex- and age-specific prevalence of sarcopenia is shown in Table II. Sarcopenia and non-sarcopenia were diagnosed in 223 and 819 patients, respectively. The total prevalence of sarcopenia was 31.0 in male and 13.9% in female patients.

Table III shows the association between sarcopenia and covariates in univariate analysis and the prevalence of sarcopenia. Between the sarcopenia and non-sarcopenia groups, there were significant differences in age, BMI, Brinkman Index, cerebral infarction/hemorrhage, history of falls and daycare use, myocardial infarction, number of oral medicines, PhA, proportion of males, QOL, history of hospitalization for heart failure, malignant disease and diabetes mellitus, age-adjusted Charlson comorbidity index, use of antidementia drugs, number of oral medicines, MMSE, GDS-15, reflux-related QOL and CSS score, restricted ventilatory impairment, CONUT score, DVS, oral frailty and EAT10 score.

In multivariate analysis, age, male sex, BMI, Brinkman Index, PhA, QOL, history of daycare use, diabetes mellitus, osteoporosis, MMSE and DVS were related to sarcopenia (Table IV).