Longitudinal study of light exposure, sleep, rest-activity rhythms, alertness and cognitive function among adults...

We evaluated the associations between daily light and sleep and rest-activity characteristics, alertness, and cognition over 1 year among participants in a study of the effects of cognitive behavioral therapy for insomnia heart failure [N = 168 participants (Mean age = 63.2 + 12.7 y; n = 72/42% women; left ventricular ejection fraction <45% = 57 (34.3%))]. We measured sleep, rest-activity rhythms, the day-to-nighttime light exposure ratio (AUC), light time above threshold (TAT), the mean timing of light above threshold (MLiT), the phase difference, and the light regularity index (LRI) using wrist actigraphy at baseline and 3, 6, and 12 months post-intervention. We used the Insomnia Severity Index, the Pittsburgh Sleep Quality Index, the PROMIS Cognitive Abilities Scale, the Psychomotor Vigilance Test, and adjusted and unadjusted general linear models. Daytime light exceeding 100 lux was associated with a later sleep midpoint, a higher circadian quotient, less intra-daily variability, and greater inter-daily stability of rest-activity rhythms. Light levels above 100 lux were associated with fewer PVT lapses, and higher AUC values with better cognitive ability (all p < 0.05). The phase difference was associated with insomnia, poorer sleep quality, and cognitive impairment over 12 months. Light levels and variability were not related to self-reported sleepiness, sleep quality, or insomnia symptoms.