“I can’t get through all my work, so I’ll cut back on sleep tonight.”
The busier we get, the more likely sleep is the first thing to go.
Cutting an hour of sleep does give you one more waking hour. But if that hour costs you focus and judgment the next day, is it really efficient?
Professor Masashi Yanagisawa of the International Institute for Integrative Sleep Medicine (WPI-IIIS) at the University of Tsukuba offers a very clear example of how sleep loss affects performance.
After staying up all night, performance drops to a level comparable to a blood alcohol concentration of about 0.1%.
So what does that actually look like?
1. One All-Nighter Brings Performance Close to Being Drunk
In an interview with Japan’s Ministry of Health, Labour and Welfare, Professor Yanagisawa explained that performance after one sleepless night is equivalent to being “thoroughly drunk,” with a blood alcohol concentration of about 0.1%.
In another interview, he described a blood alcohol concentration of 0.1% as roughly what you would reach after drinking a full bottle of wine, or about three tall cans of draft beer.
Of course, staying up all night does not actually raise the alcohol level in your body.
What is being compared is the decline in performance, such as attention and reaction speed.
One of the key studies behind this idea was published in 2000 in Occupational and Environmental Medicine.
The study involved 39 people and compared cognitive and motor performance after prolonged wakefulness with performance after drinking alcohol.
It found that after 17 to 19 hours awake, some measures of performance were equal to or worse than at a blood alcohol concentration of 0.05%.
With even longer wakefulness, performance fell to levels equivalent to a blood alcohol concentration of 0.1%.
In other words, even when you feel “tired, but I can push through,” your brain’s processing ability may be lower than you think.
2. All-Nighters Are Not the Only Concern
“I never pull all-nighters, so this doesn’t apply to me.”
Some of you may be thinking just that.
Yet one of the most intriguing findings in sleep research concerns sleep loss that builds up little by little.
A well-known study published in the journal Sleep in 2003 followed 48 healthy adults, assigned them nightly sleep opportunities of 4, 6, or 8 hours, among other conditions, and tracked their cognitive performance for up to 14 days.
In the 4-hour and 6-hour groups, attention and other aspects of cognitive performance declined day after day.
Most importantly, even a continued sleep opportunity of six hours or less was enough for the decline to accumulate each day.
Across the study, chronically limiting sleep opportunity to six hours or less eventually led to a decline in cognitive performance comparable to going one or two nights entirely without sleep.
These participants were sleeping every night.
Even so, sleep debt quietly adds up.
3. “I’m Used to Six Hours”: Are You Really?
Another intriguing point from this study is that how people felt did not match how they actually performed.
When sleep was restricted to 4 or 6 hours, cognitive performance worsened day after day.
Yet the sleepiness the participants reported did not keep worsening in the same way.
In other words,
“I’m fine on six hours of sleep these days”
is how you may feel, but that does not mean your brain’s performance has returned to normal.
Professor Yanagisawa has repeatedly pointed out this problem with chronic sleep loss: people grow used to feeling sleepy and find it harder to notice their own decline in performance.
This is a very important point for anyone who works.
When you feel intensely sleepy, you can tell yourself, “I’m off today because I didn’t sleep enough.”
But you may feel perfectly normal while your judgment and attention are slipping.
With chronic sleep loss, that may be the trickier problem.
4. Does Cutting Sleep Really Give You More Usable Time?
On paper, cutting an hour of sleep adds an hour of activity.
But at work, what matters is not only how many hours you were awake.
Focusing. Making decisions. Catching mistakes. Thinking. Reacting.
We need to take all of these abilities into account.
Especially in situations such as driving or operating machinery, where a split-second decision or reaction is directly tied to safety, the effects of sleep loss on performance cannot be taken lightly.
And this is not only about high-risk jobs.
Preparing documents, checking figures, talking with people, coming up with ideas, making important decisions.
Even in everyday work, we use our brains all day long.
Being awake for more hours is not the same as having more hours of high performance.
If cutting sleep to gain work time ends up lowering the quality of your work the next day, it may make you less efficient overall.
5. The Busier You Are, the More Sleep Belongs on Your Schedule
Of course, there will be days when work, childcare, or other circumstances make it impossible to get enough sleep.
There is no need to worry too much about a single short night.
What matters is not telling yourself “I’m used to it, so I’m fine” when sleep loss continues.
Professor Yanagisawa’s point that an all-nighter lowers performance to a level close to being drunk shows very clearly that sleep is far more than just a break.
When work gets busy,
“I’ll cut back on sleep and push a little harder”
is an easy thought to fall into.
But if you truly care about the quality of your work the next day,
getting a good night’s sleep is part of the job.
Keeping that mindset may be more important than we think.
At La HEAD, we will continue to share research on sleep, the brain, and everyday well-being in ways that are easy to bring into daily life.