Investigating the direct and indirect longitudinal relationships between social media use and life satisfaction via cosmopolitanism: A 6-year cohort study of adults.

Social media use (SMU) has experienced an exponential surge globally, prompting academic and public inquiry into its complex effects on individual well-being.Although SMU is often found to have a negligible or very small negative direct relationship with life satisfaction, the potential for SMU to indirectly foster well-being through cosmopolitanism, a sense of global citizenship, remains largely unexamined.To address this gap, we employed multivariate latent growth curve modeling on a 6-year (2019-2024) cohort of 986 Japanese adults to examine the direct, indirect, cross-sectional, and longitudinal associations between SMU, cosmopolitanism, and life satisfaction (a stable indicator of well-being).The analysis of overall SMU revealed a critical distinction between its temporal effects: The direct cross-sectional relationship with life satisfaction was statistically significant but very small and had no practical significance (b 5 .06), whereas the longitudinal relationship, indicating how change in SMU affects change in well-being, was statistically significant and practically relevant, though small in size (b 5 .24).Conversely, cosmopolitanism was a strong and consistent positive predictor of life satisfaction, both cross-sectionally (b 5 .34)and over time (b 5 .68).Critically, SMU had a significant positive indirect cross-sectional relationship with life satisfaction, mediated by cosmopolitanism (b 5 .08).However, this positive mediating effect was very small and did not sustain longitudinally.These findings clarify SMU's complex and mostly limited role while strongly underscoring cosmopolitanism as a key resource for sustained well-being. Public Policy Relevance StatementThis 6-year cohort study provides evidence for promoting well-being by establishing cosmopolitanism as a strong and enduring positive predictor of life satisfaction, significantly more so than social media use.Our findings emphasize the need for deliberate educational and policy strategies aimed at fostering cosmopolitanism, rather than relying on increased social media use volume, which shows limited positive effects and may carry a negative long-term impact on well-being.