Social Determinants of Sleep

Abstract

Humans typically sleep in highly built settings that isolate them from environmental regulators of sleep. In postindustrial, highly urbanized environments, these conditions are combined with social schedules that include long commuting times to meet strict school and work times. Together, these conditions have created a “social time” that represents a major determinant of sleep timing and quality.My studies consist of sleep data from two human study populations living in the highly urbanized city of Seattle (Washington, USA) that represent unique contexts in which social time and the built environment have distinct effects on sleep. University students have a late chronotype, or natural inclination to sleep and wake at later times of the day. Students are severely affected by their social obligations because their early school and work times conflict with their late chronotypes. The misalignment between their circadian and social times is described as social jetlag and leads to inadequate sleep duration and quality. Social jetlag and insufficient sleep duration are linked to many health conditions, such as obesity and heart disease. The Covid-19 pandemic shutdown caused workplaces and universities to become remote, which led to little to no commute and more flexibility to choose betimes. We recorded actimetry and light data in students before-Covid (2019), during-Covid (2020), and after-Covid (2021). Compared to before- and after-Covid, during-Covid there was a decrease in the discrepancy between school day and weekend sleep timing, and a longer sleep duration during school days. Light exposure timing also showed higher coherence between school days and weekends during-Covid. Importantly, while interindividual variance in sleep parameters increased during-Covid intraindividual variation did not change, suggesting that increased freedom to choose bedtimes allowed university students to default to their own circadian time and align it better with their social time. People experiencing homelessness are typically not attending school or are unemployed, and unlike students their circadian and social times are more aligned. In contrast, the main challenge they face is the lack of an appropriate environment for optimal sleep. The homeless population in Seattle also has a variety of sleeping environments. We recorded actimetry and light exposure in homeless adults living in tents, tiny houses, permanent or overnight indoor shelters during the winter and summer. We also recorded this data in adults living in stable housing conditions to compare to the unhoused communities. Our results show that both the timing of sleep and its quality is affected by the homelessness conditions and seasons. We also see a drastic difference in light exposure timing and duration due to the differences in Seattle photoperiod in summer versus winter. Both of these studies show the impact of the social environment on a persons’ sleep timing and quality.