Larks are not as productive
Cohort 1 — participants who passed all four cognitive tests.
Cohort 2 — participants who passed two tests.
Thus, the data became as accurate as possible.
What cognitive tests were used?
The following tests were used in the study:
Fluid Intelligence Test – these are 13 questions on logic and quick thinking. Each task must be completed within a limited time.
Pairs Matching – memory game. The participant is shown pairs of pictures, which are then hidden, and they need to find the matching pairs.
Reaction Time Test — pressing a button when cards match on the screen. This is a reaction speed test.
Prospective Memory Test – a tricky test where you first need to remember one instruction and then execute a completely different one. A typical example: they told you to press the blue button, but you need to press the orange one.
Sleep parameters: how much, when and how
Now to the main sleep parameters that were considered in the study:
Sleep duration — participants answered how many hours they sleep per day. The responses were divided into three categories:
Short nap: <7 hours.
Normal sleep: 7–9 hours.
Long sleep: >9 hours.
Chronotype – this is the time of day at which a person is most active:
Larks (active in the morning).
Owls (active in the evening).
Intermediate (neither this nor that).
Sleep quality – presence of insomnia. Participants were asked how often they suffered from insomnia or woke up in the middle of the night.
Results
Now to the point. What conclusions can we draw from the data?
Sleep duration
Perhaps the most important metric to consider is the number of hours you sleep. The study confirmed the old truth: 7–9 hours of sleep is the gold standard for maximum productivity. Here's what the results look like in the graphs:
Graph A for Cohort 1 clearly shows that cognitive scores peak at 6-9 hours of sleep. This creates an inverted U-shaped curve: cognitive functions work best in this range. When you're sleeping less than 6 hourscognitive activity begins to decline – this is a fact 
. Too little sleep is a productivity killer. If you think you can just get more sleep, then bad news: sleep more than 9 hours – is also harmful to the brain. Apparently, too much rest can overload your brain. 
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In graph B for Cohort 2 everything is a little more interesting. Here, cognitive performance remains stable between 5 and 9 hours of sleep, but once sleep time passes 9 hours, cognitive performance drops sharply. There is a direct connection between the amount of sleep you get and how quickly your brain thinks and solves problems.
Chronotype and its effect on the brain
Now let's talk about chronotype. The study showed that if you are a night owl, there is no need to worry: your brain may be fine! On the contrary, the data suggests that “owls” and intermediate types demonstrate better cognitive abilitiesthan larks.
Graph A for Cohort 1 shows that “owls” And intermediate types show higher cognitive scores than larks. This may be due to the fact that later chronotypes are better suited to perform cognitive tasks that require more thinking and creativity. 
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Cohort 2 (Graph B) shows a similar pattern, although the difference between chronotypes is less pronounced.
Your chronotype directly affects how quickly and effectively you solve problems. The closer you are to an “owl”, the better your cognitive abilities.
Insomnia
Now let's talk about sleep quality and insomnia. Unexpectedly, insomnia had an impact minimal impact on cognitive abilities. Although logic dictates that sleepless nights should reduce productivity, studies have not shown large differences between those who suffer from insomnia and those who sleep well.
In Graph A for Cohort 1, you can see that the difference in cognitive scores between people who have insomnia and those who don't. minimal. The difference is only a few hundredths of a point on the global z-score (β = -0.05, p > 0.05), which is not significant.
Graph B for Cohort 2 shows similar results. Even if you sometimes suffer from insomnia, it doesn't hurt your productivity as much as you might expect.
With insomnia, everything is not as scary as it might seem. Even if you can't always get enough sleep, it's not a disaster for your cognitive functions. However, this does not mean that you should give up on good sleep.
Influence of health and lifestyle factors
Another interesting aspect of the study is the impact health And lifestyle on cognitive abilities. Factors such as age, floor, diabetes and even alcohol can significantly affect brain productivity.
Floor: Women had lower cognitive scores than men in both cohorts
. This may be because the cognitive tasks used in the study are more suitable for men.Age: Aging is a predictable factor. The older the participants, the lower their cognitive abilities
.Diabetes: Participants with diabetes had lower cognitive performance
.Alcohol: It turned out that moderate alcohol consumption has a positive effect on cognitive abilities compared to abstainers
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. This may be because the cognitive tasks used in the study are more suitable for men.
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.Conclusions: how much sleep to be smarter?
Let's summarize. It turns out that being smart is not as difficult as becoming an Olympic champion, but there are still some rules of the game.
7-9 hours of sleep is the gold standard
Forget about trying to sleep 4 hours a day like Elon Musk, and don't think that you will become a genius if you sleep 10 hours a day. 6-9 hours – this is your comfort zone for the brain. Anything less is the path to zombie mode. Anything more is a direct road to oversleeping and loss of mental acuity.
Chronotype is important: owls, you win
If you're an owl, relax. Don't listen to these early risers who claim that only getting up early guarantees success. No, you can still be smarter than themif you just leave your night vigils. Focus on getting your 7-9 hours of sleep and your brain won't let you down. Larks, sorry, but the owls are already getting their second wind while you're just lacing up your sneakers for your morning run.
Insomnia is not as bad as it might seem
Okay, if you sometimes toss and turn and can’t sleep, don’t panic. Sure, it's not cool, but your brain won't immediately turn to mush. Yes, you won't become Sherlock after a sleepless night, but you won't turn into Watson either. The main thing is don’t make it a habit.
It's time to think about yourself
In short, it's time to reconsider your habits. You already know that sleep is powerbut now you know How And When use it to the maximum. So here's a question for you: how many hours do you sleep? And most importantly: When will you finally go to bed tonight?
And remember: if anyone tells you that sleeping a lot is for wimps, just show them these graphs.
