Science of Sleep Patterns

I’m sure anyone can tell me how much sleep you’re “supposed” to get. 7 – 8 hours, preferably at night time, right?

Image from The Simpsons

Or maybe you’ll be really technical and fancy and reply that it depends on your individual circumstances and that some people have an optimum 9-hour sleep and that others are fine on just 5.

And you’ve probably heard that it’s better for us to sleep at night, in fitting with our Circadian rhythm, and so it’s not so great if you’re a night-shift worker!

But what does the science and history of sleep patterns really say about it?

We used to sleep in two blocks

Until roughly the 1600s, humans would regularly sleep in two distinct periods, both about 4 hours long. They would go to bed an hour or two after sunset, then sleep for roughly four hours, before waking up again for another hour or two. In this time they’d read, pray, even talk with others or neighbours, and then falling back to sleep for another 4 hours or so ready to wake up with the sun again the next day.

Between the 1600s and 1800s, people gradually shifted to preferring a single block of sleep. What was the reason for that? The fact that city streets and public areas were starting to be lit at night. These were initially oil lamps and later progressed to various forms of gas lighting and much later to electric streetlights.

This meant that people were staying up later in the evening and so didn’t necessarily have time for their double sleep and so shifted to sleep more in a single block. Literature references to “first sleep” and “second sleep” had completely dropped away by the 19th century, roughly coinciding with the Industrial Revolution, where people were working the majority of the day, and shifting towards the sleeping patterns of today – namely that sleep is crammed into a relatively brief (let’s be honest, less than 8 hours for most people), chunk of time.

Interestingly, the rise of reported insomnia coincided with the wide-scale shift towards monophasic sleep, suggesting that perhaps people who suffer from insomnia would do better following a biphasic sleep schedule.

But what’s our more “natural” state?

The psychiatrist Thomas Wehr conducted a study on sleep in the early 1990s to try and understand what natural human sleep cycles were. He designed a scenario where participants were subjected to a 14-hour period of darkness. After several weeks of adjustment, the people started waking after about 4 hours of sleep, staying awake for 1 – 3 hours, then returning to sleep for another 4 hours.

These results indicated that we do have a natural biological inclination towards biphasic sleep (although this original study did not appear to discuss the mental/emotional effects of this particular sleeping pattern, later studies suggest that it may reduce stress and insomnia).

But, whatever our natural or biological state, it certainly hasn’t caught on. While this study and other research into biphasic sleep has been well-received and it’s suggested that it may improve quality of sleep, it hasn’t exactly been implemented by many. After all, most of us stay up late, either by choice or necessity and simply don’t feel like we have the time to dedicate to this sleep cycle. And almost no-one’s heard of it!

So perhaps it would be better for our sleep quality, but in modern society, it hardly seems feasible. But if you want to take a 4-hour sleep, get up at 1am to do an hour or two of study, reading or a midnight snack, then go for it!

As for how much you should get in your single sleep period, aiming for 7 – 9 hours is a good estimate for most people! But make sure you’re getting enough, if you’re not convinced, read this previous post on sleep deprivation!

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