Cultural and health perspectives of circadian rhythms and human sleep

Circadian rhythms (CRs) are regulated by the body's internal biological clock and influence various physiological processes such as sleep-wake cycles, hormone secretion, cardiovascular activity, core body temperature, and metabolism. Disruption to these rhythms due to irregular sleep schedules, shift work, artificial light exposure, and modern lifestyle changes are associated with adverse health outcomes. This review examines how human biological clocks have been shaped by evolutionary adaptations to natural light-dark cycles, developmental shifts in chronotype across the lifespan, and cultural factors that structure sleep behaviour across societies. It draws on evidence of segmented sleep patterns in early human societies and age-related shifts from delayed sleep in adolescence to earlier sleep-wake patterns in older adulthood. It further explores how urbanization, changes in work and social schedules, and the expansion of digital technologies and artificial light contribute to circadian misalignment. Databases such as Google Scholar, Scopus, PubMed, and Web of Science were searched systematically in accordance with PRISMA guidelines. Following a screening process, 26 studies met the eligibility criteria and were included in the final synthesis. The selected literature was examined from an anthropological perspective to understand the cross-cultural variation in sleep patterns and to explore how social organization and technological environments shape temporal behaviour. The thematic synthesis highlights how human sleep patterns have evolved, how chronotypes shift with age, how sociocultural practices shape sleep diversity across groups, and how modern lifestyles contribute to circadian misalignment. Drawing on global context and emerging evidence from India, this review identifies areas for future research and emphasizes the need to integrate biological and socio-cultural perspectives to promote overall health and well-being.