Light exposure at night and subjective and objective sleep parameters in patients with schizophrenia: A cross-sectional analysis of the LENS study

Introduction: Nighttime light exposure has been reported to be associated with sleep problems in the general population. This study aimed to investigate the association between nighttime light exposure and both subjective and objective sleep parameters in patients with schizophrenia, who often experience sleep disturbances. Methods: This cross-sectional study included 225 outpatients with schizophrenia who participated in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. Sleep was subjectively measured using the Pittsburgh Sleep Quality Index and objectively evaluated over 7 consecutive days using a wrist-worn actigraphy, respectively. Nighttime light exposure (from bedtime to rising time) was measured using an actigraphy and a portable photometer placed at the patient's bedside. Results: The median nighttime illuminance measured using the actigraphy and photometer was 1.4 lux (interquartile range [IQR], 0.5–4.5) and 4.1 lux (IQR, 1.0–15.4), respectively. After adjusting for potential confounding factors, the highest quartile of nighttime illuminance measured using the actigraphy was significantly associated with lower sleep efficiency by 10.0%, lower total sleep time by 55.6 minutes, longer sleep onset time by 0.2 log minutes, and longer wake after sleep onset by 31.0 minutes, than the lowest quartile. Similarly, an association was observed between nighttime illuminance measured using the photometer and each sleep parameter. Whereas, subjective sleep parameter was not significantly associated with nighttime light exposure. Conclusions: Nighttime light exposure was significantly associated with objective sleep parameters in patients with schizophrenia. Further longitudinal studies are needed to clarify this association.