Seasonal and daily variation in indoor light and temperature associate with sleep disturbance in dementia

Mechanisms regulating human sleep and physiology have evolved in response to rhythmic variation in environmental variables driven by the Earth’s rotation around its axis and the sun. To what extent these mechanisms are operable in vulnerable people who are primarily exposed to the indoor environment remains unknown. We analysed 26,523 days of data from environmental sensors and a contactless behaviour-and-physiology sensor tracking bed occupancy, heart and breathing rate in 70 people living with dementia (PLWD). Indoor light and temperature, sleep timing, duration and fragmentation as well as the timing of the heart rate minimum all varied across seasons. Beyond the effects of season, higher bedroom temperature and less bright indoor daytime light associated with more disrupted sleep and higher respiratory rate. This sensitivity of sleep and physiology to ecologically relevant variations in indoor environmental variables implies that implementing approaches to control indoor light and temperature can improve sleep.