Get 7 to 8 hours of sleep each night; do not treat 6 hours as enough

Two weeks in a row of only 6 hours a night, and brain performance falls to about the level of two full nights with no sleep. The problem is you do not feel it. Self-rated sleepiness rises for the first few days then stops rising; people on 6 hours score as sleepy as people on 4 hours. So the sense that “6 hours is enough for me” is not reliable.

Cost

No money. You need to leave 1 to 2 more hours each day for sleep. Going to bed earlier takes a little willpower.

Benefit

48 healthy adults aged 21 to 38 slept only 6 hours a night for 14 days straight. Their cognitive performance fell cumulatively, to about the level of 2 full nights with no sleep. Self-rated sleepiness rose only in the first few days, then barely rose further. Self-rated sleepiness did not differ between the 6-hour and 4-hour groups. This was a randomized controlled trial (RCT). Separately, short total sleep loss (acute sleep deprivation, no more than 48 hours) had an effect size g = -0.776 on simple attention lapses and g = -0.125 on reasoning accuracy. That part pooled 70 studies.

Notes

The main point is that “I do not feel sleepy” is not proof you have slept enough. People who sleep 6 hours long-term only feel used to it; performance has not caught up. The pooled part is about a full night awake. “Chronic short sleep” is backed by only one randomized controlled trial. How sleep duration links to death risk is counted separately; see Section 2, Item 13 (about 7 hours a night): that side uses mortality, and the 7-hour band has the lowest risk.

Sources · 2

1. Van Dongen, Maislin, Mullington & Dinges (2003). The cumulative cost of additional wakefulness. Sleep. doi.org/10.1093/sleep/26.2.117
2. Lim & Dinges (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin. doi.org/10.1037/a0018883