To sleep in or not to sleep in? Science seems as conflicted as the rest of us

While too little sleep is bad for you, so is too much, and no one really knows what the sweet spot is – welcome to the relatively-new world of sleep research

Having strange or vivid dreams since the coronavirus outbreak started? You're not alone. Getty Images

Feeling groggy this morning? Welcome to the club: around 90 per cent of UAE residents reportedly get less than eight hours sleep a night. And the effect is more than just drifting off at your desk.

Studies have shown that not getting enough sleep can lead to ill-health and an early grave. But now there may be a remedy — making up for lost sleep at the weekend.

A study of the sleeping habits of more than 38,000 Swedish adults found the detrimental effects of getting barely five hours sleep during the week was cancelled out by getting at least nine hours per night during the weekend.

The findings, reported in the Journal of Sleep Research, have provoked controversy among sleep researchers, who have long argued it’s impossible to catch up on lost sleep.

While one may feel temporarily revived by a decent lie-in, previous research suggested that the cumulative effect of inadequate sleep can not be undone. Studies on animals have found that the effects may even include permanent brain damage.

The authors of the new research themselves admit their findings are open to other interpretations, and need corroboration. That seems wise in the light of what is known about sleeping, which most of us spend around one-third of our lives doing.

Why do we do sleep?

The most obvious explanation is to conserve energy. But studies have found that a whole night’s sleep cuts our energy use by just 150 calories — barely 5 to 10 per cent of our total daily energy expenditure, which is equivalent to a 30 gram bar of chocolate.  

Yet at the same time, sleep must be doing something important. Every living thing from fruitflies to blue whales devotes a chunk of their life to it in one form or another, despite the fact that the act of sleep leaves them vulnerable to predators.

One widely-held theory is that sleep is vital for healthy brain function. Research suggests that the reduced sensory input gives the brain time to do some cleaning out and repair for the next day’s hard thinking.

But last year, researchers in the US showed that even a type of jellyfish lacking any brain at all seems to slumber at night, becoming far less responsive to stimuli like food.

Whatever its purpose, it’s becoming clear that too much sleep is at least as bad as too little.

Is there such a thing as too much sleep?

Inadequate sleep has long been associated with health effects ranging from obesity and diabetes to heart attacks to stroke. Last year, a comprehensive review of the evidence from over 150 studies published in the journal Sleep Medicine showed that getting less than six hours of sleep a night increased the risk of early death by around 12 per cent compared to those getting an hour or so more.  

Now the same team of Japanese researchers has carried out a similarly comprehensive review of the impact of too much sleep.

Published this month in Sleep Medicine Reviews, the findings show the risk of early death increases by almost 40 per cent among those spending more than nine hours asleep each night.

Quite why, however, remains unknown. It’s not even clear if the link between time asleep and health effects is genuine or not.

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It’s possible that sleeping either a lot or very little is just a symptom of the real cause of the strokes and heart attacks.

What isn’t in doubt is that not getting enough sleep seriously undermines mental performance. Studies show that key functions like memory, vigilance and decision-making plummet when we’re deprived of the sleep we need.  

But how much is that? As ever, there’s little consensus. Some researchers dismiss the oft-quoted figure of eight hours as lacking solid scientific support.

If there is a consensus, it’s reflected in guidance given by the US-based National Sleep Foundation.

Issued in 2015, this stresses the need for different amounts of sleep at different times of our lives.

According to the NSF, while pre-schoolers aged 3 to 5 should be getting around 10 to 13 hours, teenagers between 14 and 17 need eight to 10 hours, while adults need around seven to nine hours.

But the NSF also concedes that some individuals can cope perfectly well on as little as six hours and as much as 10.

All this raises some questions about headline-grabbing polls suggesting that virtually all of us are staggering around like zombies. 

For example, that statistic that 90 per cent of UAE residents are sleep deprived, which emerged from a survey by the health insurance firm Bupa Global, was based on the assumption that everyone needs at least eight hours a night.

In common with many other such surveys, its findings were also based on self-reported responses. While far simpler and cheaper than monitoring people, this can lead to unreliable conclusions — as nutritionists have found after checking the food diaries of obese people.

This has led some researchers to question the widely-accepted notion that there’s a global crisis of sleep deprivation, caused by our always-on, screen-gazing lives.

A 2012 survey of international trends in sleep duration by researchers at the University of Sydney found no consistent pattern between the 1960s to 2000s.

The truth is that sleep research is still in its infancy, and it’s high time the scientific community woke up to this.

Robert Matthews is Visiting Professor of Science at Aston University, Birmingham, UK