The U-Shaped Mortality Curve Epidemiological data consistently show a U-shaped or J-shaped association between sleep duration and all-cause mortality. Individuals sleeping approximately 7 hours per night exhibit the lowest risk of death.

• Short Sleep (<6–7 hours): Associated with accelerated biological aging, metabolic dysregulation, and higher risks of cardiovascular disease and respiratory mortality.

• Long Sleep (>8–9 hours): Linked to a 30% higher risk of dying compared to normal sleepers, potentially reflecting underlying systemic inflammation, frailty, or sleep fragmentation rather than a restorative benefit.

Molecular Mechanisms: "Circadian Aging" The circadian clock governs the timing of gene expression, metabolic flux, and genomic repair. Aging is associated with a dampening of these rhythms, a process termed "ci ...