Why sleep is a major performance lever
There's a book I really like: Why We Sleep by Matthew Walker.
Matthew Walker is a professor of neuroscience and psychology at UC Berkeley and the founder of a lab dedicated to sleep research. He's one of the leading references in the field.
We're not sleep specialists. The goal here is simply to share the most useful and least-known takeaways from his work - especially the ones that directly impact energy, focus, and your ability to work effectively.
Sleep is a vital function, not a luxury
Almost all living beings - including insects - need sleep.
The fact that sleep has been preserved through evolution shows how essential it is.
Sleep plays a fundamental role in:
- memory,
- learning,
- focus,
- physical and mental health.
It's probably the most powerful lever we have to stay healthy and perform over the long term.
The three key functions of sleep for the brain
Matthew Walker explains that sleep serves three essential brain functions, all tied to memory and learning.
Consolidate long-term memory
Your brain stores information in two places:
- the hippocampus, which handles short-term memory and has limited capacity,
- the cortex, which stores long-term memory.
During sleep, information is transferred from the hippocampus to the cortex.
This both secures important memories and frees up space so you can learn new things the next day.
Filter out useless information
Sleep also helps delete low-value memories and information.
Without that nightly cleanup, your brain would be saturated with useless data, hurting decision-making and focus.
Strengthen procedural ("muscle") memory
Sleep also improves what people call "muscle memory."
It's common to notice that a technical gesture or a difficult piece of music feels smoother after a night of sleep, even without extra practice.
Sleep also boosts creativity and problem-solving
Through dreaming phases, sleep helps create connections between past experiences and current problems.
It works a bit like visualization techniques used by elite athletes.
Result: you become more creative, more intuitive, and better at solving complex problems.
How many hours should you sleep?
Most researchers agree on a range of 7 to 9 hours per night for adults.
Contrary to a very common belief, sleeping less is not a sign of high performance.
The less you sleep, the more health risks increase - including cardiovascular, metabolic, and cognitive risks.
Less than 1% of the population is believed to be genetically able to sleep under 6 hours long-term without negative consequences.
Sleep loss significantly reduces focus.
For example, driving after only 4 hours of sleep increases accident risk by 12x.
Sleeping enough isn't enough: you need good sleep
Beyond duration, sleep quality is decisive.
Here are five practical habits that can significantly improve your nights.
1. Reduce screen exposure at night
Natural light helps regulate melatonin (the sleep hormone) through your circadian rhythm.
Artificial light - especially the blue light from screens - disrupts that mechanism.
It reduces melatonin production and delays falling asleep.
Ideally, avoid screens at night.
If you can't, enable blue-light filters on your devices.
2. Lower the bedroom temperature
A drop in temperature is an important biological signal for sleep onset.
In natural environments, temperature falls at night.
Try to keep your bedroom between 62 and 64°F (17-18°C) to support better sleep quality.
3. Limit alcohol
Alcohol can make you feel like you fall asleep faster, but it significantly degrades sleep quality.
In particular, it reduces REM sleep, especially after more than a couple of drinks.
Result: less restorative sleep, even if the total duration seems fine.
4. Watch caffeine
Caffeine has a half-life of about 6 hours.
That means a coffee at noon can leave about 25% of its caffeine in your body at midnight.
Even if you fall asleep easily, caffeine can reduce deep sleep, sometimes significantly.
To be safe, avoid coffee and tea after 2 PM.
5. Avoid the snooze button
Your alarm triggers a stress response.
Hitting snooze multiplies those micro-stress events and makes waking up worse.
Ideally, wake up at a fixed time, without snooze, and if possible without an alarm.
When that's not possible, simply reducing snooze is already a big improvement.
Sleep is the foundation of learning and decision-making
Sleep helps you learn more effectively, and sleeping after learning helps consolidate information.
On the flip side, sleep loss increases decision fatigue - a topic we'll dig into in
decision fatigue: why your decisions get worse late in the day.
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