The "8 hours of sleep" rule has been repeated so often it feels like scientific fact. But where does it come from, and does the evidence support it?
The real science of sleep cycles
Sleep happens in 90-minute cycles. A full night of 6 cycles (9 hours) is better than an incomplete 7th cycle waking you mid-deep-sleep. Quality matters more than quantity.
Chronotype matters more than sleep duration. A natural night owl forced to wake at 6am is functionally sleep-deprived even after 8 hours.
What you can control
Consistency of sleep and wake time matters more than duration. Your circadian rhythm is a clock — keep it accurate, and it will serve you well regardless of whether you sleep 6.5 or 8 hours.
