Mental disorders, cancers, and cardiovascular diseases mediate the associations of psychosocial factors with well-being and ikigai: a population-based cohort study

While the role of psychosocial factors in well-being appears plausible, evidence is still limited in Asian populations, and the underlying mechanisms remain unclear. We applied the g-formula to JPHC-NEXT data to examine the longitudinal association of social support, social trust, and social network (assessed via marital status, contact with relatives, contacts with friends, and group associations) at baseline with well-being and ikigai (purpose in life) at five-year follow-up. Causal mediation analysis was used to evaluate the total mediating role of three types of illnesses: mental disorders, cancers, and cardiovascular diseases. We evaluated exposures, mediators, and outcomes at three distinct time points, carefully addressed confounding, and accounted for both exposure-mediator and mediator-mediator interactions. We included 46,480 participants in the well-being analysis and 46,482 participants in the ikigai analysis. The mean age was 61.9 ± 8.60 years, and 25,240 participants (54.3 %) were women. Psychosocial factors were consistently associated with an increased risk of diminished well-being. The adjusted RRs (95 % confidence intervals) were: low social trust, 2.49 (2.08–3.07); absence of contacts with relatives, 1.48 (1.26–1.76); and absence of group associations, 1.32 (1.16–1.51). Similar adjusted RRs were observed for diminished ikigai. Proportion mediated by three types of illnesses for the pathways to diminished well-being and ikigai was: low social trust, 9.0 % and 18.0 %; absence of contacts with relatives, 26.0 % and 27.0 %; and absence of group associations, 14.2 % and 31.1 %, respectively. Psychosocial factors may influence individuals’ illnesses, which, in turn, lead to well-being—a crucial outcome for both individuals and society as a whole.