Associations between adverse childhood experiences and insomnia: The moderating role of social capital in a three-year longitudinal study from the Japan Gerontological Evaluation Study.

Objective: Adverse childhood experiences (ACEs) are linked to sleep disturbances later in life. Social capital may promote better sleep among older adults, but its moderating role remains unclear. We examined whether social capital modifies the ACE-insomnia association. Methods: Longitudinal data from the Japan Gerontological Evaluation Study (2013-2016, Japan) included 8890 adults aged 65 years and older. Insomnia in 2016 was assessed with the Athens Insomnia Scale. ACEs were measured retrospectively in 2016, and social capital in 2013 across civic participation, social cohesion and reciprocity. Poisson regression estimated relative risks (RR) of insomnia. Effect-measure modification (EMM) was evaluated on multiplicative and additive scales. Results: More ACEs were associated with a higher probability of insomnia (per +1 ACE: RR = 1.19; 95 % CI = 1.15, 1.23). Higher civic participation, social cohesion, and reciprocity were inversely associated with insomnia (RRs = 0.87-0.94). EMM was limited: civic participation showed a small interaction in the amplifying direction (multiplicative RR = 1.04; p = 0.03), whereas social cohesion and reciprocity showed no interaction. Conclusions: Social capital showed limited modification of the ACE-insomnia association. Social cohesion remained independently protective, while civic participation slightly amplified the association. Fostering cohesive, supportive communities may promote sleep health in later life, including among those with ACE histories.