Feeling sleepy?

We all know that too little sleep is bad for us. Matthew Walker, a UC Berkeley sleep scientist and author of the best-selling Why We Sleep, has gone so far as to declare: "The shorter you sleep, the shorter your life." However, some researchers fear that our concerns about not getting enough sleep are becoming overblown — and that, ironically, they could be making the problem worse. In this feature, we take a look at evidence that "too little" sleep isn't always the disaster that it's held up to be.

It's not always about a lack of sleep

You'll be familiar with the chronotype concepts of larks (early to bed and early to rise) and owls (late to bed, and late to rise). Most kids start out as larks, but during adolescence, many shift to becoming owls. Waking up late is fine for teenagers at the weekends, but not during the school week. Unsurprisingly, then, various studies have found that delaying the time school starts improves academic results for this age-group, and many sleep scientists and paediatricians support such a policy. It's been assumed that this is because it allows teens to get a decent night's sleep. But there's some evidence that this may not be the reason. A recent study of Dutch secondary school pupils, published in Scientific Reports, found that owls did get poorer exam grades, but this effect was largely independent of sleep duration.

This suggests that even when owls get "enough" sleep, they don't do as well as larks on exams. And this, it seems, is because exams are often administered in the mornings, when owls aren't at their cognitive peak. When owls took exams in the afternoon, closer to that peak, they achieved similar grades as larks. This was especially true for science subjects. Of course, if the school day starts later, then exams start later — and this could be a better fit for many teens' chronotype. What this all means, though, is that, in many cases, trying to get teens to go to bed earlier, to sleep for longer, may not make as much of a difference to their performance at school as has been claimed.

Cause or effect?

Anxiety, OCD, ADHD, schizophrenia, PTSD… all kinds of mental health problems are associated with sleep problems, too. It's now recognised that the relationship is circular, with mental illness and insomnia exacerbating each other. It's not as simple, then, as a lack of sleep causing symptoms. And certainly, there's evidence that stress early in life can set you up for insomnia much later. One study found that children who grew up in families with high levels of conflict went on to be more likely to have insomnia as adults. This held even when any sleep problems or depression during childhood were controlled for in the analysis — so it wasn't a case of participants who'd had trouble sleeping as kids still having these difficulties as adults. And when it comes to depression, the links between sleep and symptoms can be surprising…

A surprising therapy

Depriving depressed people of sleep works as an effective treatment. This was shown in series of studies starting almost 50 years ago. But it has become a standard therapy only recently. Healthy people deprived of sleep will generally find that their mood worsens. But for people with depression, staying awake for at least a night can do the opposite (temporarily, anyway). The impacts are rapid, and work on most patients, as a study in Denmark, for example, has found. Exactly how the treatment works is still debated, but it's thought to shock a sluggish biological clock.

Sleep doesn't always improve memory

The evidence that sleep is important for memory is pretty overwhelming. But, recently, at least one study has challenged the idea that sleep always brings memory benefits. Given the experimental record, the researchers had expected to find that eye-witnesses who were given the chance to sleep would be better at identifying suspects the following day. But they weren't…

This was a big study: 2000 participants watched a brief video of a man stealing a laptop from an office. Twelve hours later, they were asked to identify him from a line-up. Half had slept during this time, but, contrary to expectations, they were no more accurate than the others at picking out the perpetrator. More work is needed to try to clarify why not.

Effects can be indirect

No doubt you've heard that a lack of sleep isn't just bad for your mental but your physical health. Women who get less sleep are indeed more likely to develop obesity, type 2 diabetes and heart disease, for example. But the major reason for these effects seems to be indirect: women who sleep poorly tend to make poorer food choices, going for higher-calorie, energy-dense foods. These choices are certainly related to a lack of quality sleep, but they aren't an inevitable result of it. The same team behind this finding suspect, meanwhile, that a poor diet can cause poor sleep: "It's also possible that poor diet has a negative impact on women's sleep quality", notes lead author Faris Zuraikat, at Columbia University. "Eating more could also cause gastrointestinal discomfort, for instance, making it harder to fall asleep or remain asleep."

Some poor sleepers don't suffer at all

Just how bad is insomnia anyway…? There are a lot of people out there who technically do suffer from insomnia, but who don't believe, or realise, that they do, and these people experience no distress or anxiety, and are no more impaired in terms of daily fatigue than those who get good sleep. What's more, a massive increase in hypertension (high blood pressure) was observed among those who regarded themselves as having insomnia, but not among the "non-complaining poor sleepers". The same review found that 37% of people who think they have insomnia actually sleep normally, and having an "insomnia identity" was more predictive of daytime impairment than poor sleep. Other research has found, meanwhile, that worrying about not getting enough sleep can itself lead to prolonged insomnia.

Headlines that make people worry that they're not getting enough sleep could themselves, then, cause some of the problems they're describing. Which brings me back to the start of this feature…. There's plenty of evidence that a good quantity of regular quality sleep is important. But how we think about the way we sleep is important, too.

About the author

Emma Young (@EmmaELYoung) is a staff writer at BPS Research Digest.