0420 Post-Waking Light Exposure Is Associated with Next-Night Sleep Efficiency Among Veterans with Insomnia and a History of Traumatic Brain Injury

Abstract Introduction Risk for insomnia is elevated after traumatic brain injury (TBI) and can impair daily functioning. Previous research suggests that light exposure has time-of-day-dependent associations with sleep. However, longitudinal investigations into daily light exposure and subsequent sleep under naturalistic conditions are limited, and it is unclear if sleep is responsive to day-to-day variation in light exposure. Accordingly, this study sought to evaluate how between- and within-person differences in light exposure were associated with sleep efficiency during post-TBI insomnia. Methods This was a secondary analysis of data from 27 veterans with insomnia and past TBI. Actigraphy and sleep diaries were collected for one week. For each individual sleep episode, actigraphy-measured light was extracted for the hour following their previous awakening (i.e., post-waking) and the hour preceding the current lights-off time. Person-level means were calculated to compare average light exposure across participants. Person-scaled values, reflecting the degree to which daily light exposure differed from the participant’s average, were used to evaluate within-person associations. Robust linear mixed modeling was used to estimate the associations between light exposure variables and sleep efficiency. Independent variables were person-level means and the person-scaled values for the post-waking and pre-sleep windows. Covariates included the previous night’s sleep efficiency, study day, weekends, age, gender, and TBI severity. Results Sleep efficiency was positively associated with person-level means in post-waking light exposure (β = 0.49, SE = 0.18, 95% CI: 0.13 – 0.85). It was also positively associated with person-scaled post-waking light exposure (β = 0.08, SE = 0.04, 95% CI: 0.01 – 0.15), corresponding to ~1.0% greater sleep efficiency per one standard deviation increase in personal light exposure. Light exposure prior to attempting sleep was not associated with sleep efficiency. Similar results were found when exploring two- and three-hour exposure windows. Conclusion Participants with brighter average post-waking light exposure had higher sleep efficiency. Importantly, within-person associations were also identified, such that participants had higher sleep efficiency following days during which they were exposed to greater-than-average post-waking light. Increasing post-waking light exposure may be a powerful intervention for insomnia following TBI. Support (if any) Department of Veterans Affairs Rehabilitation Research & Development Service (award # D4414-P)