Preliminary findings from the world's largest sleep study reveal that adults averaging 7 to 8 hours of sleep nightly exhibit superior cognitive performance compared to those sleeping less or more. Launched in June 2017, this landmark online survey drew over 40,000 participants worldwide, combining detailed questionnaires with cognitive tasks to examine real-world sleep patterns.
"We aimed to capture global sleep habits beyond lab settings," explains the lead researcher. "Participants shared extensive details—from medications and age to location and education—allowing us to account for key influencing factors."
Notably, about half reported under 6.3 hours nightly, an hour short of recommendations. Strikingly, those averaging four hours or less performed cognitively like individuals nearly nine years older.
Sleep's impact proved consistent across ages: 7 to 8 hours optimized brain function universally, with deficits from too little or too much sleep unaffected by participant age.
"This aligns with medical advice for physical health—7 to 8 hours is ideal for cognitive peak performance," notes the study's lead author. "Excess sleep impairs the brain as much as deprivation."
Reasoning and verbal skills suffered most from suboptimal sleep, while short-term memory held up better. This contrasts with total sleep deprivation studies, indicating chronic partial loss affects the brain differently than all-nighters.
Positively, above-average sleep the prior night enhanced performance, even beyond usual amounts.
