Abstract
Indoor light levels are low in urban housing, disrupting health and wellbeing. Low light intensities are associated with poor light entrainment and decreased daily rhythms' amplitude, which is associated with an increased risk of metabolic disturbances, cancers, and mood. This problem is exacerbated in older adults who are likely more impacted by mistimed exposure to indoor lights. Importantly, the age-related attenuation of circadian rhythms and reduction in transmission of short-wavelength light may underlie circadian/sleep alterations in older adults. However, studies indicate that improving indoor light conditions can alleviate age-related sleep/circadian disturbances. Here, we aim to assess the real-world impact of indoor light supplementation during daytime on activity-rest rhythms, wellbeing, and personal light exposure of older adults. In three cities (Bologna, Amsterdam, Tartu), 1,500 older adults (500 for each city) will be recruited in this population-based epidemiological design. Out of the 500 participants, 250 will be randomly selected to be exposed to indoor, blue-enriched light for 12 weeks and compared to 250 participants that will not have any indoor light intervention (control). A 2-week baseline will be carried out to assess daily activity patterns, sleep, and light exposure through wrist-worn actigraphy and wearable light sensors. In addition, participants will complete an activity diary in which they are asked when they eat, sleep, and are outdoors. Additionally, we will collect subjective measures of sleep quality, chronotype, and mood. After 12 weeks of light supplementation, the same measures will be re-assessed again for a 2-week period, allowing the quantification of the effects of the 12-week experimental lighting change. The results from this study will generate a scientific evidence base to support effective lighting guidelines aimed at improving citizens' health and wellbeing.