Background: Engaging in social activities, interacting with peers, and participating in community events may promote health and well-being. Recently, interventions leveraging information and communications technology have emerged as potent tools for promoting social connections and well-being. Particularly, messenger apps have becomean integral part of our daily lives, facilitating communication, information dissemination, and social interaction. However, there remains a gap in the literature regarding the utilization of widely adopted messenger apps for this purpose. Objective: This study aimed to evaluate the impact of messenger app-based information provision aimed at promoting social participation on the enhancement of subjective well-being among Japanese community-dwelling adults. Methods: A 2-arm, parallel-group randomized controlled trial was conducted from October 2022 to January 2023 in the Kashiwa-no-ha campus area, Japan-an urban community with active local events. A total of 358 community-dwelling adults who use messenger apps daily were recruited for the study. Of these, 235 (65.6%) participants completed the follow-up survey. Participants were randomly assigned to either the intervention group, receiving the health benefits of social participation and information about local events or spots via a messenger app, or the control group, receiving general health information. The primary outcome was subjective happiness after the intervention, measured on an 11-point scale ranging from 0 (Unhappy) to 10 (Happy). Secondary outcomesincluded life satisfaction, meaning of life, purpose in life, and participation in local events. The outcomeswere analyzed with t tests (2-tailed) and multivariable regression based on the intention-to-treat method. Results: After the intervention, the intervention group reported a mean happiness score of 7.7 (SD 1.7), while the control group reported a score of 7.5 (SD 2.0), with no statistically significant difference (P=.40). Multivariable linear regression analysis adjusted for baseline outcome values and covariates showed that the coefficient of the intervention for life satisfaction was 0.30 (95% CI -0.07 to 0.68; P =.12), whilethatfor meaning of lifewas 0.33 (95% CI -0.03 to 0.70; P =.07). Therewas no significant difference in event participation rates between the2 groups during the study period (P=.22). However, 82.2% (102/124) of the intervention group acknowledged the utility of the event information provided. Conclusions:Messenger app-based information provision did not yield a significant increase in subjective happiness, while there was a positive but not significant trend in life satisfaction. The findings underscore the need for more intensive intervention in future studies to harness the potential of digital interventions. Trial Registration: UMIN Clinical Trials Registry UMIN000049047; https://tinyurl.com/2zzrrae8
