Every adult needs exactly eight hours of sleep per night.

Analysis

Major sleep-medicine bodies — the American Academy of Sleep Medicine and the National Sleep Foundation — recommend a range (7–9 hours for most adults), not a single number.

Population studies show a U-shaped mortality curve: both very short (under ~6 hours) and very long (over ~9 hours) habitual sleep correlate with worse outcomes, but the bottom of the curve is wide rather than pointed at eight.

Individual variation is substantial. A small fraction of the population are documented short sleepers who function well on 6 hours or fewer; others need closer to 9. Sleep quality and timing matter at least as much as raw duration.

The engine returns Refuted on the literal 'exactly eight' framing while flagging the related claim 'most adults benefit from 7–9 hours' as Supported.

Sources Weighed

• Sleep, Watson et al. (AASM/SRS consensus, 2015)
  Professional society consensus
  Recommends 7+ hours as a range, not a fixed number.
• Sleep Health, Hirshkowitz et al. (NSF, 2015)
  Expert panel recommendation
  Provides age-stratified ranges, including 7–9h for adults.
• Sleep Medicine Reviews, Cappuccio et al. (2010)
  Meta-analysis
  Documents U-shaped relationship between sleep duration and mortality.