Exposure to brighter light after waking is associated with better sleep efficiency among veterans with insomnia and a history of traumatic brain injury.

INTRODUCTION

Insomnia risk is elevated after traumatic brain injury (TBI) and can impair daily functioning. This study sought to evaluate how average and day-to-day changes in naturalistic light exposure were associated with sleep efficiency during post-TBI insomnia.

METHODS

This was a secondary analysis of observational data from 28 veterans with insomnia and past TBI. Over a week, light was measured in the hour after each sleep episode's awakening (i.e., post-waking) and the hour preceding each sleep episode's lights off time (i.e., pre-sleep). Person-specific averages and day-to-day changes (i.e., changes from a person's average) in light were calculated for the post-waking and pre-sleep windows. Robust linear mixed modeling was used to estimate the associations between light variables and actigraphy-measured sleep efficiency.

RESULTS

Average post-waking light exposure was positively associated with average sleep efficiency (β = 0.44, 95% confidence interval [CI]: 0.08 - 0.89). Day-to-day changes in post-waking light-exposure were positively associated with next-night sleep efficiency (β = 0.08, 95% CI: 0.01 - 0.14). Exploratory analyses revealed that this relationship was only present for veterans with low average post-waking light, such that a change from 10- to 100-lux from one day to the next was associated with a 5% increase in sleep efficiency. Light exposure prior to attempting sleep was not associated with sleep efficiency.

CONCLUSION

Exposure to brighter light after waking up was associated with better sleep efficiency among veterans with insomnia and a history of TBI. For those with limited post-waking light exposure, light-based interventions may offer rapid improvement of insomnia symptoms.