Do I actually need eight hours of sleep?

Daniel E. LiebermanPhD · paleoanthropologist, Edwin M. Lerner II Professor of Biological Sciences, Harvard

No, and being told you do is part of why you sleep badly

What it rests onTwo strands. People in societies without electric light and phones sleep roughly six to seven hours, not eight, so the eight-hour figure is not a recovered natural baseline. And the epidemiological association for most people is better at around seven hours than at eight. His larger point is mechanistic and about anxiety: telling people they need eight hours, a perfect mattress, silence and darkness raises cortisol, and an aroused, nervous person does not sleep.

Matthew WalkerPhD · neuroscientist

Seven to eight hours of sleep, which means budgeting more than eight hours in bed

What it rests onSleep duration and sleep opportunity are not the same quantity: he states that to obtain seven hours of sleep an average healthy adult needs a sleep opportunity of about eight hours and fifteen minutes in bed. On duration he cites a twin study of 21,268 people in which the lowest mortality risk fell at seven to eight hours, with sleep under seven hours associated with a 26 percent increase in mortality risk in men and 21 percent in women, alongside experimental work in which six-hour nights produced cumulative neurocognitive impairment that participants did not notice.