Shedding light on sleep: Investigating the impact of light on sleep and neurobehavioral outcomes in older adults with sleep disturbance

Sleep is a fundamental biological process and plays a vital role in promoting and maintaining healthy ageing. However, sleep disturbances are common in older adults and are associated with a range of negative health and functional outcomes. Pharmacotherapy is the most commonly used to treat sleep disturbance in older adults despite the significant side effects. There is a need to investigate other treatment options for sleep disturbances in older people. Light therapy has been used as a non-pharmacological intervention for treating sleep and mental disorders. However, the evidence for the therapeutic efficacy of light for sleep disturbance, and especially older people is mixed. Therefore, the overarching objective of this thesis was to investigate the impact of light on sleep and daytime function in older adults with self-reported poor sleep. The first chapter of this thesis provides an overview of sleep architecture changes associated with ageing, along with the consequences of sleep disturbances and management strategies. The chapter reviews the extant literature on the impact of light on sleep, focusing on studies conducted in naturalistic and controlled laboratory-based environments. In the second chapter of this thesis, a synthesis of published studies examining the effects of lighting interventions on objective sleep in patients with sleep or circadian rhythm disorders was conducted. The scoping review identified a limited number of studies. Due to the inconsistency of findings across these studies, we were unable to draw definitive conclusions regarding the impact of lighting interventions on sleep in patients with sleep or circadian rhythm disorders. The third chapter was an empirical study examining light exposure and sleep in community-dwelling older adults during the COVID-19 pandemic, which allowed an observation during restricted living conditions and subsequent free-living conditions when the lockdown restrictions were completed. This study showed light exposure levels were higher during the restricted living conditions compared to the free-living conditions; however, light exposure did not influence the timing or quality of actigraphic-derived or subjective sleep. The fourth chapter was a second study which used a pilot randomised, double-blind, controlled, crossover design to investigate the effects of daytime blue-enriched light on objective sleep using polysomnography with high-density electroencephalogram (EEG) and daytime function in older adults with subjectively reported poor sleep. This study showed a three-day exposure to blue-enriched light did not improve sleep macro-architecture nor daytime function. However, high-density EEG analysis showed increased sigma power during N1 and N2 sleep after the blue light exposure. The overall finding of the thesis was that light exposure, whether in naturalistic or laboratory-based settings, had no significant influence on sleep architecture or daytime function in older adults. However, it remains unclear whether longer periods of light exposure, or exposure to light at different intensities, wavelengths, or timings, may change sleep in older populations.<p></p>