Matthew Walker wants us all to take sleep more seriously.   “No aspect of our biology is left unscathed by sleep deprivation,” he says. “And yet no one is doing anything about it. When have you ever seen an NHS poster urging sleep? When did a doctor prescribe not sleeping pills, but sleep itself? Sleep loss costs the UK economy more than £30bn a year in lost revenue, or 2% of GDP. I could double the NHS budget if only they would institute policies to mandate or powerfully encourage sleep.”

Walker, a Liverpool-born sleep scientist, is now the director of the Center for Human Sleep Science at the University of California, Berkeley.

As the line between work and leisure grows ever more blurred, we are worrying more about our sleep. Indeed, it is Walker’s conviction, as recounted to Rachel Cooke in The Observer newspaper, that we are in the midst of a “catastrophic sleep-loss epidemic”, the consequences of which are far graver than any of us could imagine.

Walker has spent the last four-and-a-half years writing Why We Sleep, a complex but urgent book that examines the effects of this epidemic close up, the idea being that once people know of the powerful links between sleep loss and, among other things, Alzheimer’s, cancer, diabetes, obesity and anxiety, they will try harder to get the recommended eight hours a night.

Why, exactly, are we so sleep-deprived?

In 1942, less than 8% of the British population was trying to survive on six hours or less of sleep a night; in 2017, almost one in two people is. “First, we electrified the night,” Walker says. “Light is a profound degrader of our sleep. Second, there is the issue of work: not only the porous borders between when you start and finish, but longer commuter times, too. No one wants to give up time with their family or entertainment, so they give up sleep instead. And anxiety plays a part. We’re a lonelier, more depressed society. Alcohol and caffeine are more widely available. All of these are the enemies of sleep.”

Walker believes, too, that in the developed world sleep is associated with weakness, even shame. “We have stigmatised sleep with the label of laziness. We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting.

In case you’re wondering, the number of people who can survive on five hours of sleep or less without any impairment, expressed as a percent of the population and rounded to a whole number, is zero.

Does he take his own advice when it comes to sleep? “Yes. I give myself a non-negotiable eight-hour sleep opportunity every night, and I keep very regular hours: if there is one thing I tell people, it’s to go to bed and to wake up at the same time every day, no matter what. I take my sleep incredibly seriously because I have seen the evidence. Once you know that after just one night of only four or five hours’ sleep, your natural killer cells – the ones that attack the cancer cells that appear in your body every day – drop by 70%, how could you not?”

And if he is struck by the curse of insomnia? He turns on a light and reads for a while.

More than 20 large-scale epidemiological studies all report the same clear finding: the shorter your sleep, the shorter your life.

To take just one example, adults aged 45 years or older who sleep less than six hours a night are 200% more likely to have a heart attack or stroke in their lifetime, as compared with those sleeping seven or eight hours a night. A lack of sleep also appears to hijack the body’s effective control of blood sugar, the cells of the sleep-deprived appearing, in experiments, to become less responsive to insulin, thus causing a prediabetic state of hyperglycaemia. When your sleep becomes short, moreover, you are susceptible to weight gain. Among the reasons for this are the fact that inadequate sleep decreases levels of the satiety-signalling hormone, leptin, and increases levels of the hunger-signalling hormone, ghrelin. “I’m not going to say that the obesity crisis is caused by the sleep-loss epidemic alone,” says Walker. “It’s not. But processed food and sedentary lifestyles do not adequately explain its rise. Something is missing. It’s now clear that sleep is that third ingredient.”

Sleep has a powerful effect on the immune system, which is why, when we have flu, our first instinct is to go to bed: our body is trying to sleep itself well. Reduce sleep even for a single night, and your resilience is drastically reduced. As Walker has already said, studies show that short sleep can affect our cancer-fighting immune cells. And getting too little sleep across the adult lifespan will also significantly raise your risk of developing Alzheimer’s disease.  (In his book, Walker notes “unscientifically” that he has always found it curious that Margaret Thatcher and Ronald Reagan, both of whom were vocal about how little sleep they needed, both went on to develop the disease.)

And then there is sleep’s effect on mental health. When your mother told you that everything would look better in the morning, she was wise. Walker’s book includes a long section on dreams (which, says Walker, contrary to Dr Freud, cannot be analysed). He suggests that dreaming is a soothing balm. Deep sleep – the part when we begin to dream – is a therapeutic state during which we cast off the emotional charge of our experiences, making them easier to bear. Sleep, or a lack of it, also affects our mood more generally. Brain scans carried out by Walker revealed a 60% amplification in the reactivity of the amygdala – a key spot for triggering anger and rage – in those who were sleep-deprived.

How is it possible to tell if a person is sleep-deprived? Walker thinks we should trust our instincts. Those who would sleep on if their alarm clock was turned off are simply not getting enough. Ditto those who need caffeine in the afternoon to stay awake. “I see it all the time,” he says. “I get on a flight at 10am when people should be at peak alert, and I look around, and half of the plane has immediately fallen asleep.”

So what can the individual do? First, they should avoid pulling “all-nighters”, at their desks or on the dancefloor. Second, they should start thinking about sleep as a kind of work, like going to the gym. “People use alarms to wake up,” Walker says. “So why don’t we have a bedtime alarm to tell us we’ve got half an hour, that we should start cycling down?” We should start thinking of midnight more in terms of its original meaning: as the middle of the night. Sleeping pills, by the way, are to be avoided. Among other things, they can have a deleterious effect on memory.

Here Walker talks with academics at Berkeley about sleep and the brain.

A longer version of this article by Rachel Cooke first appeared in The Observer

© Guardian News and Media Limited 2017. This is a shorter version of a report in the THE WEEK, 4 October 2017

Why We Sleep: The New Science of Sleep and Dreams by Matthew Walker is published by Allen Lane at £20.