You can't ask me that: How well do you sleep?

“Did you sleep well?” It’s what we ask overnight guests at the breakfast table. It’s a morning variation on “how are you?” and as is the case with that tricky question, you’re only ever supposed to answer in the positive. “Yes, I did sleep well, thanks. Very comfy bed.” And yet for more and more of us, the opposite is true. We didn’t sleep well at all. We certainly didn’t sleep for long enough.

Hardly a week goes by without an article somewhere reminding us that we should be getting eight hours a night. It’s the World Health Organisation’s recommendation. Eight hours. That’s a third of a day. And still hold down a job and have a semblance of a family life and find the time to brush your hair? Fat chance, right?

In 1990, we Brits may have been averaging eight hours sleep, but according to a First Direct survey, by 1995 we’d lost 25 minutes a night. By 2013, research by The Sleep Council discovered that more than 70 per cent of us were sleeping for less than seven hours. In 2017, a Travelodge survey suggested we weren’t even managing that, clocking up an average of six hours and 14 minutes. Yearly, that’s a whole 28 days’ worth of shut-eye less than we got in the nineties. No wonder we’re knackered.

But do we really need eight hours? What about those people who say they can get by on fewer? Like Boris Johnson, who sleeps for five hours a day? Or Margaret Thatcher, who was notorious for needing only four? She would work until one in the morning and still be up in time to listen to Farming Today at half five. Trump naturally goes one better, claiming he can get by on just three hours a night. That frees up an awful lot of extra tweeting time.

And even if most of us are getting a month’s less sleep a year than recommended, it doesn’t seem to have any demonstrable effects, does it? We still get up and go to work and have coherent conversations. We’re not really suffering, right?

A closer look at the data suggests that perhaps we are. When I asked Matthew Walker, professor of neuroscience and psychology at UC Berkeley and director of the Centre of Human Sleep Science, what he thought, he put it bluntly. “The number of people that appear to be able to survive on six hours of sleep or less, without showing any objective impairment to their mind or body, rounded to a whole number and expressed as a per cent of the population is… zero.” He further claimed, “As soon as people drop below seven hours we can start to measure objective impairments.”

Indeed, sleep studies have linked sleep deprivation to a range of ill effects from poor memory and concentration to mood changes, to lowered levels of testosterone in men, to increased risk of accidents and falls. Not getting enough sleep may even make us fat by interfering with the production of leptin, the appetite-regulating hormone, while increasing levels of leptin’s evil twin ghrelin, the hormone that makes us feel hungry.

There have been studies to suggest that restricting sleep to four hours or less over several nights might induce a “diabetic-like” state of hypoglycaemia. Then there’s the effect of poor sleep on our immune systems. There’s evidence that the so-called “natural killer cells”, which patrol our bodies helping to prevent the growth of cancerous tumours, may be suppressed by lack of shut-eye.

The bad news continues. In 2017 a study by researchers at Stanford University and the Washington Medical School found that just a few nights of poor sleep correlated with increased levels of amyloid beta and tau, two proteins that have been implicated in Alzheimer’s Disease.

In her latter years, Margaret Thatcher succumbed to dementia. It’s been suggested that the exacting nature of her job staved off the condition’s onset. But what if getting more sleep would have meant that Thatcher remained free of dementia symptoms for even longer? In his book Why we sleep: the new science of sleep and dreams, Matthew Walker seems to suggest as much. He writes, “Unscientifically, I have always found it curious that Margaret Thatcher and Ronald Reagan – two heads of state that were very vocal, if not proud, about sleeping only four to five hours a night – both went on to develop the ruthless disease.”

Walker explained to me that our brains and central nervous system rely on something called the glymphatic system to clear away waste products. This “sewage system” for the brain kicks into high gear during deep sleep. If you’re not getting enough deep sleep, your brain isn’t being properly cleansed and therefore those waste products – such as amyloid beta – build up to harmful levels.

Walker told me, “I hope Trump takes some of this information regarding the tragic ends of Thatcher and Reagan to heart… He might want to reprioritise his goals regarding sleep.”

But never mind the increased risk of Alzheimer’s. The short term effects of a lack of sleep on the presidency don’t look so good either. Walker pointed out that “after being awake for twenty hours straight, you are as cognitively impaired as you would be if you were legally drunk.”

So it sounds as though Trump should consider getting an extra hour’s sleep to be more coherent and consistent in his communication and avoid the dreaded “covfefe” or worse. After all, which of us hasn’t mixed up “would” and “would not” after a bad night’s kip?

Unlike Trump, Winston Churchill took getting enough sleep very seriously, saying: “Never stand up when you can sit down. And never sit down when you can lie down.” Churchill developed his habit of napping for two hours every afternoon when he was First Lord of the Admiralty during World War One.

His colleague, First Sea Lord John Fisher, was an early riser, already at his desk by five. However, in the afternoons, Fisher’s energy and effectiveness flagged. Seeing this, Churchill changed his daily routine to compliment Fisher’s. He pushed back his waking time from seven until eight and took an afternoon nap so that he could work until two in the morning without losing focus. In that way, Churchill ensured that he and Fisher “constituted an almost unsleeping watch throughout the day and night.”

I asked Walker if naps count towards a daily tally of eight hours? The answer is, “Yes and no”. There is a school of thought that we could serve all our sleep needs through napping rather than waste a third of the day in bed. “Uberman sleep”, otherwise known as “polyphasic sleep”, recommends six 20-minute naps spaced equally throughout the day. Walker is unequivocal about it. “You can’t do the Uberman schedule. That’s deleterious.” However he does agree that hunter-gatherer societies sleep to a different schedule to the one we’re familiar with. They indulge in biphasic sleep. Six and half hours a night and a siesta during the day.

Biphasic sleep is a pattern that seems to be genetically pre-programmed into all humans. Studies of brain wave activity show that we all experience a hard-wired drop in alertness somewhere between two and four in the afternoon, known as the “post-prandial drop”. It used to be thought this was linked to the digestion of lunch, but it happens whether we eat or not. It seems we are programmed to nap. And if we can nap as a regular time without finding it affects our ability to drop off at night, Walker is all for it.

However he recommends we nap for no longer than 40 minutes and if we are struggling to sleep at night, we should avoid trying to snatch 40 winks during the day, since napping acts like “releasing a pressure valve” on the natural urge to sleep that builds up while we’re awake. Release that valve and you’re back to square one, unable to sleep when you really want to.

Assuming we can’t find the time for a regular nap, how can we get a better night’s sleep? In his book, Walker recommends keeping regular hours, ensuring proper darkness (dim the lights before bed and avoid screens in the hour before sleep), keeping the bedroom cool, and avoiding caffeine after midday.

Father of the Protestant Reformation, Martin Luther is credited with saying: “Whoever drinks beer, he is quick to sleep; whoever sleeps long, does not sin; whoever does not sin, enters Heaven! Thus, let us drink beer!” Alas, Luther’s logic was flawed. Walker also rules out the tradition of the nightcap as an aid to a good night. While a drink may help you drop off more quickly, it won’t help your sleep quality. Alcohol leads to broken sleep and less time spent in the REM or dreaming phase. Never mind...

As might be expected, Walker is evangelical about getting enough sleep. For him, eight hours kip is a non-negotiable part of his own daily routine. “The very best health insurance policy is an eight-hour night of sleep and for purely selfish reasons, I will indulge in that every night.”

There’s no doubt that modern life can make getting a good night’s rest difficult and for many of us it’s unlikely we’ll be able to change the way we live and work to accommodate significantly better sleeping habits anytime soon. But it’s definitely worth trying. From better powers of concentration to better sex, from increasing our chances of staving off disease, getting enough sleep changes everything. As Walker puts it: “Sleep is Mother Nature’s best effort yet at immortality.”