Sleep 7 to 8 hours a night, and don't treat 6 hours as enough

Moderate value
Evidence A
Saves time
Free
Takes time daily
Some willpower

In plain words

After two weeks of only 6 hours of sleep a night, your mental performance drops to about the level of going two days and nights without sleep. The trouble is that you can't feel it. Self-rated sleepiness stops rising after the first few days, and people sleeping 6 hours rate themselves as sleepy as people sleeping 4. So “6 hours is enough for me” is itself a symptom of not sleeping enough.

Cost: Free. You have to set aside 1 to 2 more hours a day for sleep. Going to bed earlier takes a little willpower.
What you get: 48 healthy adults aged 21 to 38 slept only 6 hours a night for 14 days in a row. Their mental performance declined cumulatively, falling to the level of going 2 nights in a row with no sleep at all. Their self-rated sleepiness rose only over the first few days and then barely increased. Self-rated sleepiness in the 6-hour group and the 4-hour group did not differ. This was a controlled trial that randomly split people into groups (RCT). In addition, short periods without sleep (acute sleep deprivation, up to 48 hours) had an effect size of g = -0.776 on simple attention lapses and g = -0.125 on reasoning accuracy. That part pooled 70 studies.
Notes: “I don't feel sleepy” is not evidence that you have slept enough. People who sleep 6 hours for a long time have only gotten used to the feeling, and their performance has not caught up. The pooled part covers whole nights without sleep. “Long-term short sleep” is supported by only one randomized controlled trial. How long you sleep and the risk of death are counted separately; see §2.13 (sleep about 7 hours a night): that item counts by mortality, and the 7-hour group has the lowest risk.
Evidence grade: A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources: Van Dongen, Maislin, Mullington & Dinges (2003). The cumulative cost of additional wakefulness. Sleep. https://doi.org/10.1093/sleep/26.2.117
Lim & Dinges (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin. https://doi.org/10.1037/a0018883

Mentioned in

Translated from the Chinese original. Original book, section 3, tip 3. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer