Background/Objectives: School refusal tendency is an important school adaptation issue, but its upstream psychosocial correlates remain insufficiently understood. We examined whether baseline multidimensional social interaction was prospectively associated with later school refusal tendency and whether an exploratory statistical indirect association was observed through psychological and behavioral difficulties. Methods: This three-year longitudinal observational study included 314 students in grades 5–9 aged ≥12 years at baseline in 2020 and followed through 2023. Social interaction was assessed using the Index of Social Interaction (ISI), psychological and behavioral difficulties using the parent-reported Strengths and Difficulties Questionnaire (SDQ), and school refusal tendency using a parent-reported binary item. Adjusted regression and Monte Carlo product-of-coefficients analyses were conducted. Results: School refusal tendency was observed in 84 participants (26.8%). Higher baseline ISI scores were associated with lower follow-up SDQ total difficulties (β = −0.830, 95% CI: −1.033 to −0.627) and lower odds of school refusal tendency (OR = 0.832, 95% CI: 0.741–0.934). The indirect effect through follow-up SDQ total difficulties was significant (−0.120, 95% CI: −0.193 to −0.055). After adjustment for baseline SDQ total difficulties, the indirect effect remained significant (−0.067, 95% CI: −0.124 to −0.020); Firth and parsimonious models yielded similar estimates. Baseline-domain-adjusted analyses retained indirect effects through emotional symptoms, peer problems, and internalizing problems. Conclusions: Higher baseline multidimensional social interaction was associated with lower subsequent psychological and behavioral difficulties and school refusal tendency. Baseline-SDQ-adjusted analyses supported an exploratory indirect association, particularly through internalizing-related difficulties; however, concurrent assessment of follow-up SDQ and school refusal precludes causal interpretation.

This longitudinal observational study examined the association between multidimensional social interaction and motor function among community-dwelling older Japanese adults over a 9-year follow-up period (2011–2020). Using data from the Community Empowerment and Care Cohort Study in suburban central Japan, the analysis included 304 participants aged 65 years and older who had no baseline motor impairment and completed follow-up. Social interaction was assessed using the Index of Social Interaction (ISI), and motor function was evaluated using the Kihon Checklist. After adjustment for age, IADL status, and baseline motor function score, higher total ISI was significantly associated with higher odds of having normal motor function at follow-up (odds ratio [OR]: 1.21; 95% confidence interval [CI]: 1.01–1.47; p = 0.044). Among the ISI subscales, social curiosity showed a significant association with motor function at follow-up (OR: 1.39; 95% CI 1.01–1.92; p = 0.045). These findings suggest that baseline social interaction, particularly social curiosity, may be a relevant predictive factor for later motor function among community-dwelling older adults. However, because the analysis was observational and conditioned on survival and continued participation, the findings should be interpreted as predictive associations rather than causal effects.

This study examined the relationship between changes in social interactions and sleep status, specifically sleep duration and restoration, among older adults in Japan to inform interventions for healthy aging. A 6-year longitudinal study (2017–2023) was conducted under the Community Empowerment and Care Project in suburban Japan. A total of 473 older adults with normal sleep in 2017 were followed. Sleep duration (< 6 h defined as deprivation) and sleep restoration (subjective restfulness) were assessed according to national guidelines. Social interaction was measured using the 18-item Index of Social Interaction (ISI). Changes in the ISI were analyzed continuously and categorically. Lo-gistic regression models were used to examine the association between ISI changes and sleep outcomes. After six years, 16.3% of the participants experienced sleep deprivation, and 26.2% reported non-restorative sleep. Declining ISI scores were significantly asso-ciated with a higher risk of sleep deprivation and non-restorative sleep. Persistently low or declining ISI scores increased the odds of poor sleep. A one-point ISI increase re-duced the risk of sleep deprivation and non-restorative sleep, even after adjusting for confounders. Negative or persistently low social interaction is linked to worse sleep outcomes; maintaining or improving social interaction may protect sleep quality.

Background/Objectives: Social interaction may be associated with sleep health, but longitudinal evidence among working-age adults is limited, and ceiling-concentrated scores may complicate linear modeling. We examined baseline social interaction, three-year follow-up sleep quality, and the exploratory role of life satisfaction. Methods: Data came from 487 adults aged 20–58 years surveyed in 2020 and 2023. Social interaction was assessed using the 18-item Index of Social Interaction (ISI). Normal sleep required at least 6 h of sleep and adequate restfulness. Models were adjusted for baseline sleep, demographics, lifestyle, health, depression, and anxiety. The ISI functional form was assessed using natural cubic splines and a piecewise model with a knot at 14. Results: In the initial linear summary model, a higher ISI score was associated with normal follow-up sleep (OR = 1.24, 95% CI: 1.09–1.42). The spline model fit better (likelihood-ratio χ² = 19.69, df = 2, p < 0.001). Below 14, each 1-point increase was associated with higher odds of normal sleep (OR = 2.81, 95% CI: 1.64–4.82); no additional association was observed at 14 or higher (OR = 0.99, 95% CI: 0.83–1.19). The ISI × life satisfaction interaction was sensitive to parameterization. Spline-based analysis showed an average indirect association through life satisfaction (estimate = 0.0077, 95% bootstrap CI: 0.0019–0.0153), while direct and total associations were not significant. ISI was associated with restfulness but not duration. Conclusions: The ISI–sleep association was nonlinear, concentrated in lower scores, and plateaued near the upper end. Life-satisfaction findings were exploratory; concurrent measurement precluded causal mediation inference.