Published papers

Although the economic burden of multimorbidity is a growing global challenge, the contribution of multimorbidity in patients with high medical expenses remains unclear. We aimed to clarify multimorbidity patterns that have a large impact on medical costs in the Japanese population. We conducted a cross-sectional study using health insurance claims data provided by the Japan Health Insurance Association. Latent class analysis (LCA) was used to identify multimorbidity patterns in 1,698,902 patients who had the top 10% of total medical costs in 2015. The present parameters of the LCA model included 68 disease labels that were frequent among this population. Moreover, subgroup analysis was performed using a generalized linear model (GLM) to assess the factors influencing annual medical cost and 5-year mortality. As a result of obtaining 30 latent classes, the kidney disease class required the most expensive cost per capita, while the highest portion (28.6%) of the total medical cost was spent on metabolic syndrome (MetS) classes, which were characterized by hypertension, dyslipidemia, and type 2 diabetes. GLM applied to patients with MetS classes showed that cardiovascular diseases or complex conditions, including malignancies, were powerful determinants of medical cost and mortality. MetS was classified into 7 classes based on real-world data and accounts for a large portion of the total medical costs. MetS classes with cardiovascular diseases or complex conditions, including malignancies, have a significant impact on medical costs and mortality.

Background: The potential for developing frailty exists in middle-aged and older adults. While obesity and metabolic syndrome (MetS) increase the risk of frailty in older adults, this relationship remains unclear in middle-aged adults, who are prone to developing lifestyle-related diseases. Objective: To examine the effect of overweight/obesity and MetS on frailty development in middle-aged and older Japanese adults using real-world data. Methods: This nationwide cohort study used exhaustive health insurance claims data of 3,958,708 Japanese people from 2015 to 2019 provided by the Japan Health Insurance Association. Participants aged ≥35 and < 70 years who received health checkups in 2015 were included. Multivariate logistic regression was used to assess the effect of body mass index (BMI) and MetS or MetS components (i.e., diabetes, hypertension, and dyslipidemia) in 2015 on frailty risk assessed using the hospital frailty risk score in 2019. Additionally, a subgroup analysis was performed to examine the interaction effects of MetS components and 4-year weight change (%) on frailty risk among participants who were overweight and obese (BMI ≥25 kg/m2). Results: In 2019, 7204 (0.2%) and 253,671 (6.4%) participants were at high and intermediate frailty risks, respectively. Obesity and MetS were independently associated with intermediate/high frailty risk (odds ratio (OR) 1.36, p < 0.05; OR 1.23, p < 0.05, respectively) and high frailty risk (OR 1.80, p < 0.05; OR 1.37, p < 0.05, respectively) in all participants. Although all MetS components were frailty risk factors, these effects diminished with age in both sexes. Subgroup analysis of patients with diabetes revealed that 5%–10% weight loss was associated with reduced frailty risk in both sexes. Conclusions: Obesity, MetS, and MetS components were independent frailty risk factors in middle-aged and older Japanese adults. Weight loss of up to 10% over 4 years prevented frailty in patients with diabetes who were overweight and obese.

Non-restorative sleep (NRS) affects not only individuals’ health, but also company productivity, highlighting the importance of measures in the workplace to improve sleep. This study aimed to examine the clustering of the presence of restorative sleep (RS) and lifestyle habits in a Japanese working population and to explore the characteristics of these clusters. The subjects were 58,150 Japanese working men aged 40−59 years who underwent health check-ups across the country from April 2015 to March 2016. Data for the presence of RS, the frequency and amount of drinking, smoking/exercise habits, and body mass index obtained from health check-ups were clustered with latent class analysis. In addition, the characteristics of each cluster were examined from the perspectives of lifestyle-related disease-associated blood test results obtained from health check-ups and the status of medical treatment at medical institutions as determined from medical claims data. Consequently, RS and lifestyle habits were found to form five clusters. The “NRS, no exercise, drinkers” cluster showed the highest probability of not achieving RS. An “Obese, occasional binge drinkers” cluster with a higher percentage of patients with sleep-apnea syndrome and a “Nondrinkers” cluster with proportions of those taking sleeping pills/anxiolytics and antidepressants/antipsychotics were observed. Furthermore, the “Daily smokers and drinkers” and “RS and drinkers” clusters showed a relatively high probability of achieving RS. These findings suggest that some individuals may not be aware of the sleep disorders caused by their drinking and smoking habits. Measures to improve sleep must be tailored to the characteristics of each cluster.

This study aimed to clarify the trajectory of BMI alongside age-related changes in height and weight among Japanese adults. Data from annual health checkups between 2015 and 2020 by the Japan Health Insurance Association were retrospectively analyzed. A total of 4,777,891 men and 3,378,003 women (age 35–69 years) were stratified into 14 subgroups based on sex and 5-year age categories. We used linear mixed-effects model to estimate values for each outcome, with six-time points (2015–2020) as the independent variable. Mean BMI changes were positive across all subgroups, indicating a trend of increasing BMI (men, 0.02 to 0.14 kg/m2/year; women, 0.05 to 0.16 kg/m2/year). In younger subgroups, the changed were relatively large, with the weight transitions mirroring those of BMI. However, the mean changes were negative (men, −0.06 kg/year; women, −0.01 kg/year) in the oldest subgroups. Height reduction increased with age across subgroups (men, −0.14 to −0.03 cm/year; women, −0.18 to −0.01 cm/year). In conclusion, BMI tended to increase with age in both sexes across all age groups of Japanese adults. The increase in BMI appeared to be influenced by weight gain in young to middle age, whereas height reduction influenced increased BMI in older age groups.

Background/Objectives: Predicting comprehensive patient characteristics is essential for optimal individualized rehabilitation plans for acute stroke patients. However, current models primarily predict single outcomes. This study aimed to assess the applicability of latent class analysis (LCA) in rehabilitation practice by identifying comprehensive characteristics and associated predictors in acute stroke patients. Methods: We conducted a retrospective observational study using the Japan Association of Rehabilitation Database, including 10,270 stroke patients admitted to 37 acute-care hospitals between January 2005 and March 2016. Patients were classified using LCA based on outcomes at discharge, including Functional Independence Measure (FIM), National Institutes of Health Stroke Scale (NIHSS) subscales for upper-extremity function, length of hospitalization, and discharge destination. Predictor variables at admission included age, FIM scores, NIHSS subscales for upper-extremity function, stroke type, and daily rehabilitation volume. Results: 6881 patients were classified into nine distinct classes (class size: 4–29%). Class 1, representing the mildest cases, was noted for independent ambulation and good upper limb function. Class 2 comprised those with the most severe clinical outcome. Other classes exhibited a gradient of severity, commonly encountered in clinical practice. For instance, Class 7 included right-sided paralysis with preserved motor activities of daily living (ADLs) and modified dependence in cognitive functions, such as communication. All predictors at admission were significantly associated with class membership at discharge (p < 0.001). Conclusions: LCA effectively identified unique clinical subgroups among acute stroke patients and demonstrated that key admission variables could predict class membership. This approach offers a promising insight into targeted, personalized rehabilitation practice for acute stroke patients.

Background: Suicide prevention can be significantly enhanced by time-sensitive surveillance using digital data sources like online message board. To inform more effective suicide prevention strategies, this study analyzes the temporal patterns of posts on a Japanese mental health message board—NHK’s “Facing Suicide” website—that may aid in early risk detection. Methods: We analyzed 63,046 posts from Japan’s national broadcaster (NHK) message board (1 Jan, 2008–31 Mar, 2025), stratified by gender and age (≤19, 20s, 30s, ≥40). Generalized additive models were used to model hourly, weekly, and monthly variations, with time of day included as a spline term. Results are presented as incidence rate ratios (IRRs) with 95% confidence intervals (CIs). Results: Females contributed 75.5% of posts, and the 20–29 age group was the most active (32.4%). Posting activity consistently peaked around 23:00 across all subgroups. A marked increase was observed among adolescents (≤19 years) in August (males: IRR = 1.30, 95% CI [1.05–1.61]; females: IRR = 1.55, 95% CI [1.43–1.69]), while adults showed decreases in January–February. Weekly patterns varied by subgroup; for instance, males aged 20–29 posted more on Mondays and Tuesdays (IRR = 1.17, 95% CI [1.05–1.30]). Conclusions: Online message board activity displays predictable temporal cycles with demographic-specific patterns. These findings provide an essential baseline for real-time monitoring systems to detect deviations that may signal elevated suicide risk. The August peak in adolescent posts aligns with back-to-school distress, and the late-night peaks underscore the need to provide 24-hour support services and implement automated multi-layered online intervention strategies directly within message boards. These insights can guide the development of targeted, time-sensitive suicide prevention strategies.

For older patients with displaced femoral neck fractures, in which primary osteosynthesis is usually not indicated, there are three primary prosthetic options—bipolar hemiarthroplasty (BHA), single-bearing total hip arthroplasty (SB-THA), and dual-mobility THA (DM-THA). However, the optimal choice for managing displaced femoral neck fractures remains controversial. Accordingly, this study aimed to evaluate the cost-effectiveness of BHA, SB-THA, and DM-THA in active older patients with displaced femoral neck fractures. A decision tree combined with a Markov model was employed to analyze the cost and quality-adjusted life years (QALYs) of BHA, SB-THA, and DM-THA for the management in the Japanese healthcare system. By simulating the five-year trajectory of a 75-year-old woman treated for a displaced femoral neck fracture, the cost-effectiveness of the three surgical options was evaluated. One-way sensitivity analysis and probabilistic sensitivity analysis (PSA) were used to assess parameter uncertainty. Additionally, two scenario analyses were conducted for other settings. The treatment was considered to be cost-effective when the incremental cost-effectiveness ratio (ICER) was below the 5,000,000 yen/QALY threshold. Compared with BHA, SB-THA exhibited higher costs but greater health benefits, resulting in an ICER of 1,499,440 yen/QALY. DM-THA offered additional health benefits compared with SB-THA, with an ICER of 4,145,777 yen/QALY. One-way sensitivity analysis revealed some influential parameters. PSA indicated that the probability of DM-THA, SB-THA, and BHA being cost-effective was 40.1%, 38.5%, and 21.4%, respectively. SB-THA was more cost-effective than BHA in patients aged 65–85 years, while DM-THA was more cost-effective than SB-THA in patients aged 65–75 years. The results suggest that SB-THA is a cost-effective alternative to BHA for displaced femoral neck fractures in active older patients, whereas DM-THA is more cost-effective than SB-THA in relatively younger patients. It is, therefore, recommended that orthopedic surgeons select the most appropriate surgical option based on the individual patient’s physiological age.

Background: The objective of this study was to examine the effect of the Japanese re-work program (RP) to aid in recurrent sick leave prevention. Methods: A multicenter retrospective cohort research was conducted for workers who returned to work (RTW) after sick leave due to mood disorder. Work continuation for subjects who RTW after RP participation and treatment as usual (TAU) and subjects who received TAU only were compared. The Kaplan–Meier method and Cox proportional hazard models were utilized. Additionally, propensity score matching was conducted to control for possible confounds. Results: Log-rank test of overall cohort (n = 323) showed that work continuation of RP + TAU subjects was significantly better compared to that of TAU-only subjects (p = 0.001). Multivariate analysis found a hazard rate of recurrent sick leave for TAU-only subjects of 2.121 (p = 0.001, 95% CI: 1.360–3.309). Additionally, the propensity score-matched cohort (n = 100) had similar differences (p = 0.008), with a hazard ratio of recurrent sick leave of 2.871 (p = 0.009, 95% CI: 1.302–6.331) for TAU-only subjects. Limitations: Only workers who RTW after sick leave were targeted, and no examination was made considering cases who dropped out from RP or TAU. Moreover, the sample was a non-randomized controlled trial, with propensity score matching performed. However, there was an inability to retrieve and adjust for working environment background factors after RTW. Conclusions: Work continuation of subjects with RP was observed to be significantly better, suggesting that the RP was effective for recurrent sick leave prevention.

In order to explore the factors affecting patients’ level of activities of daily living (ADL) on discharge after undergoing bipolar hemiarthroplasty or total hip arthroplasty for displaced femoral neck fractures at an acute care hospital, patient data were analyzed with the following statistical tools: multiple regression analysis (MRA), structural equation modeling (SEM), and simultaneous analysis of several groups (SASG). The Barthel Index (BI) on discharge was set as the objective variable, while age, sex, degree of dementia, BI on admission, number of days from admission to surgery, surgical option, and number of rehabilitation units per day were set as explanatory variables. Factors such as age, sex, degree of dementia, BI on admission, and number of rehabilitation units per day were significant in MRA. While not significant in MRA, the number of days from admission to surgery was significant in SEM. According to the SASG, the number of rehabilitation units per day was significant for patients without dementia but not for patients with dementia. Analysis of real-world data suggests that early surgery and rehabilitation affect ADL on discharge to a greater degree than the surgical method. For patients without dementia, longer daily rehabilitation was significantly associated with better ADL on discharge.

Objectives: This study examined the association between intensive rehabilitation for subacute stroke patients and medical costs and readmission ratio during the year after discharge. Design: This was a natural experiment study. Setting and Participants: We identified individuals with a diagnosis of cerebrovascular disorder (ICD-10: I60-I69 cerebrovascular disease) in an insurance claims database in Japan from January 2005 to December 2017. From the database, 980 patients who were admitted to a convalescent rehabilitation unit with stroke were identified. After excluding 575 patients, 405 were eligible for the study. Methods: In Japan, from April 2011, a new policy was established that allows special costs to be added as rehabilitation time increases. This policy provides an additional medical fee for inpatients in a convalescent rehabilitation unit who receive more than 120 minutes of rehabilitation therapy. We defined high-intensity rehabilitation as transfer from hospitalization to a convalescent rehabilitation unit after April 2011. Outcomes were total direct medical costs and readmission ratio during the year after discharge from the convalescent rehabilitation unit. Results: Daily rehabilitation time, total rehabilitation time, and total medical costs of the high-intensity rehabilitation group were significantly higher than those of the low-intensity rehabilitation group (P < .001, P < .001, P = .011, respectively). However, there was no significant difference in the medical costs during the year after discharge (P = .653) or in the readmission ratio (hazard ratio: 1.09, 95% confidence interval: 0.55-2.18, P = .804). Conclusions and Implications: Intensive rehabilitation did not reduce medical costs or the readmission ratio during the first year after discharge. Future studies should consider the necessary rehabilitation intensity given the severity of the patient's condition, using large sample sizes.

Objectives: To assess the applicability of Electronic Frailty Index (eFI) and Hospital Frailty Risk Score (HFRS) algorithms to Japanese administrative claims data and to evaluate their association with long-term outcomes. Study Design and Setting: A cohort study using a regional government administrative healthcare and long-term care (LTC) claims database in Japan 2014-18. Participants: Plan enrollees aged ≥50 years. Methods: We applied the two algorithms to the cohort and assessed the scores' distributions alongside enrollees' 4-year mortality and initiation of government-supported LTC. Using Cox regression and Fine-Gray models, we evaluated the association between frailty scores and outcomes as well as the models' discriminatory ability. Results: Among 827,744 enrollees, 42.8% were categorised by eFI as fit, 31.2% mild, 17.5% moderate and 8.5% severe. For HFRS, 73.0% were low, 24.3% intermediate and 2.7% high risk; 35 of 36 predictors for eFI, and 92 of 109 codes originally used for HFRS were available in the Japanese system. Relative to the lowest frailty group, the highest frailty group had hazard ratios [95% confidence interval (CI)] of 2.09 (1.98-2.21) for mortality and 2.45 (2.28-2.63) for LTC for eFI; those for HFRS were 3.79 (3.56-4.03) and 3.31 (2.87-3.82), respectively. The area under the receiver operating characteristics curves for the unadjusted model at 48 months was 0.68 for death and 0.68 for LTC for eFI, and 0.73 and 0.70, respectively, for HFRS. Conclusions: The frailty algorithms were applicable to the Japanese system and could contribute to the identifications of enrollees at risk of long-term mortality or LTC use.