Workplace Social Capital Subscales and Their Association With Depressive Symptoms in Japanese Research Institutions

Background  The challenges to workers' mental health in rapidly changing modern work environments have highlighted the crucial role of workplace social capital (WSC). However, a comprehensive examination of how its structural dimensions (bonding, bridging, linking) relate to depressive symptoms, particularly among Japanese workers and within specific occupational settings such as research institutions, is insufficient. While previous studies have explored WSC, few have rigorously differentiated these three dimensions and their independent associations with mental health outcomes, especially in the Japanese context, where unique work culture dynamics may play a role. Objective This study aimed to cross-sectionally evaluate the association between each structural dimension of WSC (bonding, bridging, linking) and depressive symptoms among workers in research institutions and related organizations in Japan. Methods  A cross-sectional web-based survey (Tsukuba Salutogenic Occupational Cohort Study: T-SOCS) was conducted in 2022, targeting 21,875 workers in institutions located in Tsukuba Science City. A total of 3861 responses were received (response rate: 17.7%), and data from 3145 valid responses with complete data were analyzed. WSC was assessed using the Japanese version of an eight-item scale to calculate the bonding, bridging, and linking scores. Depressive symptoms were evaluated using the Japanese version of the Patient Health Questionnaire-9 (PHQ-9), with a score ≥ 5 defined as "having depressive symptoms." Multiple logistic regression analysis was performed to examine the association between each WSC dimension and depressive symptoms, adjusting for personal attributes (biological sex, age, marital status, and caregiving/child presence) and occupational characteristics (employment type, job type, managerial position, and flextime availability). Results  Of the participants, 47.2% were identified as having depressive symptoms (PHQ-9 ≥ 5). After adjustment for personal and occupational factors, higher bonding WSC scores were significantly associated with lower odds of having depressive symptoms (odds ratio (OR) = 0.89; 95% CI: 0.81-0.97; p = 0.01). Similarly, higher bridging WSC scores were significantly associated with lower odds of having depressive symptoms (OR = 0.90; 95% CI: 0.81-0.99; p = 0.03). In contrast, linking WSC score showed no significant association with depressive symptoms (OR = 0.95; 95% CI: 0.89-1.01; p = 0.11). Being female, providing care, and working in administrative roles were also associated with increased odds of depressive symptoms. Conclusion In this sample of Japanese research institution workers, higher levels of horizontal WSC (bonding and bridging) were associated with fewer depressive symptoms, whereas vertical WSC (linking) was not. These findings underscore the importance of fostering horizontal SC for workers' mental health. However, the study's cross-sectional design, low response rate, and specific population limit the generalizability of our findings and preclude causal inference. Future research should employ longitudinal designs to establish causality, expand to diverse occupational groups, and explore the cultural nuances and potential mediating factors that could inform more targeted interventions.