The best sleep learned from primitive humans.

Science Girl's Conditioning Column 011

In this column, a science-minded woman who graduated from Tokyo Tech explores tips for achieving peak performance, incorporating a scientific perspective.

This month's theme is "Sleep that suits you."

There are various theories about ideal sleep duration and bedtime, but recently it has been suggested that the optimal sleep varies from person to person.

One factor that determines this is genetics.

I would like to consider optimal sleep based on the sleep patterns of tribes that still live as hunter-gatherers today.

Someone is awake 24 hours a day.

Don't you think that people who live lives free from things that disrupt sleep—like electricity, smartphones, television, and various work-related matters—are getting the optimal sleep for humans?

Researchers at the University of Toronto in Canada took note of this and actually surveyed tribes living as hunter-gatherers.

What was characteristic was that someone was always awake (1).

Why is that?

It is because a lookout is necessary to avoid being attacked by wild animals.

Factors that determine morning or evening types

According to recent research, whether you are a morning person or an evening person is determined by about 50% by genes. (2)

By maintaining diversity in sleep patterns—with people having morning-type genes and people having evening-type genes—we humans protected ourselves from external enemies.

In this way, half of the factors that determine whether you are a morning or evening type are innate and cannot be changed, but the remaining half are said to be determined by age, season, and lifestyle habits.

Generally, it seems that many people follow a pattern of being a morning type as a child, becoming an evening type upon entering adolescence, and returning to a morning type as they age.

Tribal sleep duration is the same as that of Japanese people

Now that we know there are individual differences in bedtime and wake-up time due to genes, what about sleep duration?

When two tribes in Africa and one tribe in South America that still live as hunter-gatherers were surveyed, their daily sleep duration was an average of 6.4 hours (3).

It's less than you'd imagine, isn't it?

Even so, they didn't have the word or concept of "sleep deprivation," and they apparently didn't doze off during the day.

How enviable...

Japanese people are often discussed as being "sleep deprived" compared to the rest of the world, but a 2021 survey showed an average of 6 hours and 43 minutes(4), which isalmost the same as tribes that don't know sleep deprivation.

Short sleepers and long sleepers

However, from this survey, it is premature to decide uniformly that "sleeping 7 hours is fine." The required sleep time also has individual differences.

The story that Napoleon only slept for 3 hours is famous, isn't it? On the other hand, Einstein is said to have remarked, "If I don't sleep for 9 hours, my head doesn't feel clear."

People who are fine with less than 6 hours of sleep like Napoleon are calledshort sleepers, and people who need 9 hours or more of sleep are calledlong sleepers.

Personality influences sleep time

Comparing short sleepers and long sleepers, there are apparently big differences in personality.

Short sleepers are theoptimistic type who don't worry much. Long sleepers are thetype who worry and fret when they fail.

"Worrying" and "thinking things over" tire out the brain, so it means that those who don't do that much need short sleep, while those who do it a lot need long sleep.

There are individual differences in optimal sleep

Now, summarizing what we've discussed so far, we've learned that there are "individual differences" in bedtime, wake-up time, and required sleep time.

Ideal sleep differs from person to person.

The problem is that the modern lifestyle generally follows a 9-to-5 work style.

It is set to a time zone where most people can be active, but for those who are geneticallyextreme night owls or long sleepers, it is difficult to adapt.

Strategies for those who find 9-to-5 work difficult

"Changing work hours" is quite difficult, but by making some adjustments, it might become a little easier to work.

Strategies for those who are genetically night owls

As mentioned earlier, half of it is determined by genetics, so there is no room for adjustment, but the other half is determined by age, lifestyle habits, and environment.

Soaking up the morning sun,not getting too much light at night, if you are careful about things like these and adjust your internal clock every day, you should be able to slightly alleviate the feeling that "mornings are tough."

Strategies for long sleepers

I think it is quite difficult to work 8 hours a day and also get more than 9 hours of sleep.

That is why I recommendmeditation.

The reason why long sleep is necessary is thought to be "brain fatigue." Meditation can be expected to have the effect of relieving brain fatigue.

Summary

The point was that sleep patterns are, by nature, something wherethe optimal solution differs for each person.

However, in modern times, people who are weak in the morning are labeled as "useless," and long sleepers suffer from sleep deprivation, preventing them from performing at their full potential.

According to research on sleep, it has been revealed that "productivity drops if you don't sleep for 6 hours," but this is merelya group average.

Among these, there may be people whose productivity does not drop at all, and there may be people whose productivity drops when they sleep less than 8 hours, not 6.

The fact that it hides individual variations is a limitation of research, isn't it?

Regarding sleep, information saying "You should do this!" is overflowing in the streets, but we don't know if it is "optimal for you."

I would like to observe myself carefully and think once again about what kind of sleep pattern is optimal.

P.S.

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