中島 聡美

Abstract Introduction Light information critically influences sleep and emotion regulation. Nighttime light exposure has been suggested to disrupt sleep and predict poor health outcomes. However, little is known about how sleep changes after bereavement and how sleep changes contribute to prolonged grief. We examined the association between nighttime light exposure and sleep continuity in bereaved adults. Methods In this cross-sectional study, 30 adults who had been bereaved for at least one year, wore a wrist actigraphy for seven consecutive nights. Bedroom light intensity from bedtime to rising time (BLI, lux) and sleep continuity variables were estimated from the wrist actigraphy. We tested the association between BLI and natural log-transformed sleep continuity measures and explored factors that modify this relationship in multivariable-adjusted generalized linear models. Results Nearly 40% of participants were diagnosed with current prolonged grief disorder (PGD), even after a median of 2.5 years since the loss. The mean BLI was 3.72 lux. Overall, higher BLI was associated with lower sleep continuity, independently of psychological, physical, and sleep covariates, including total sleep time, sleep midpoint, and season. This was particularly evident for sleep fragmentation index (B = 0.076; 95% CI, 0.029–0.122; exp[B] = 1.079), indicating that every 1-unit increase in BLI was associated with a 7.9% increase in sleep fragmentation index. Moreover, the association between BLI and sleep fragmentation was more robust in participants with current PGD, those who had lost a child or spouse, and those whose loss was violent or sudden than in those without each of these characteristics. Similarly, depressive symptoms, hypnotic use, and regular alcohol drinking also modified the relationship between BLI and sleep fragmentation. Conclusion These data strengthen the evidence for nighttime light exposure and sleep fragmentation. Our findings suggest that post-loss stress and vulnerability factors interact to disrupt sleep through increased light sensitivity at night. Further research is needed to determine the role of sleep fragmentation in the maintenance of and recovery from grief. Support (if any) This work was supported by the Intramural Research Grant for Neurological and Psychiatric Disorders of NCNP (Grant numbers #3-1 and #6-1) and KAKENHI (Grant numbers #20H01774 and #23H01045).