Is Sleep Enough? Why Circadian Rhythm Matters Beyond Sleep Duration

Sleep has traditionally been regarded as one of the most fundamental biological requirements for human health.Over the past several decades, extensive epidemiological and clinical research has demonstrated that insufficient sleep is associated with numerous adverse outcomes, including depression, obesity, diabetes, cardiovascular disease, cognitive decline, and increased mortality.Consequently, both sleep medicine and public health policies have focused heavily on sleep duration as the principal indicator of sleep health.Recommendations emphasizing "7-8 hours of sleep" have become widely accepted in clinical practice and public discourse.However, emerging evidence suggests that the relationship between sleep and health is substantially more complex than previously assumed.Sleep duration alone may not adequately reflect the integrity of the biological systems governing sleep and wakefulness.Increasingly, circadian rhythm timing, stability, and alignment are being recognized as critical determinants of both physical and mental health.In this context, a crucial question arises: Is obtaining enough sleep truly sufficient for maintaining optimal health?Modern society has profoundly disrupted the temporal organization of human behavior.Artificial light exposure at night, shift work, excessive screen use, irregular meal timing, globalized work schedules, and social jetlag collectively weaken endogenous circadian synchronization.Importantly, many individuals in modern environments may obtain relatively adequate sleep duration while simultaneously maintaining highly irregular sleep-wake