Adverse effects of late sleep on physical health in a large cohort of community-dwelling adults.

Aims: Sleep timing, influenced by chronotype, behavior, and circadian rhythms, is critical for human health. While previous research has linked chronotype to various health outcomes, the impact of aligning sleep timing with chronotype on physical health remains underexplored. The objective of this study is to investigate the association between chronotype, actual sleep timing, and their alignment with a spectrum of physical health outcomes.

Methods: Objective sleep timing (actigraphy, categorized as early, intermediate, or late) and chronotype (self-reported, categorized as morning, intermediate, or evening types) were derived from the UK Biobank (n=73,888 middle-aged and older adults) and used in cross-sectional and longitudinal analyses. Physical health outcomes included metabolic disorders, diabetes, obesity, hypertension, circulatory disorders, digestive disorders, respiratory disorders, and all-cause cancer based on ICD10 codes. Analyses were adjusted for demographic factors, sleep duration and sleep timing stability.

Results: As compared to morning types with early behavior (aligned), morning types with late behavior (misaligned) had an increased risk of all included physical health disorders (p's<0.001). As compared to evening-types with late behavior (aligned), however, evening-types with early behavior (misaligned) had a decreased risk of diabetes, obesity, hypertension, circulatory disorders, and respiratory disorders (p < 0.01). Longitudinal analyses, in which the likelihood of developing de novo physical health disorders was associated with chronotype, behavioral timing, and alignment between the two, confirmed cross-sectional findings.

Conclusion: Late sleep timing across chronotypes was consistently associated with adverse physical health outcomes. These findings underscore the importance of going to sleep early, regardless of preference.