When your alarm goes off in the morning & you feel as though you could keep snoozing, then you are likely not getting sufficient good quality sleep at night. If you cannot function without coffee before noon, you are probably sleep-deprived, & if you are sleep-deprived, you are not alone: according to the World Health Organization, we are in the midst of a global sleep deprivation epidemic.

Not getting enough sleep won’t just make you yawn on the Tube or wish for nap-time at your desk. According to one of the world’s leading sleep scientists, the less you sleep, the shorter your life will be. Matthew Walker is a professor of neuroscience & psychology at the University of California & he has just published the definitive manifesto on sleep science, called Why We Sleep – out this week.

Sleep deprivation (that is, sleeping 6 hours or less a night or not getting the quality of sleep you need) is linked to Alzheimer’s disease, anxiety, depression, bipolar disorder, suicide, stroke, chronic pain, cancer, diabetes, heart attack, infertility, weight gain, obesity & immune deficiency. It can damage the brain, worsen mental illness, tempt serious physical illness, weaken the immune system, rile up the nervous system, wipe out concentration, deplete productivity, eradicate creativity, ravage the body, & in extreme cases, kill. The significance of sleep, quite seriously, cannot be overstated. It’s, Walker says, more powerfully linked to our mortality than nutrition & exercise.

If you would rather look at it in positive terms, sleep is the Swiss Army Knife of medicine. It is a miraculous cure-all that, done correctly, makes us live longer, improves our memory, ignites our creativity, makes us more physically attractive, lowers our food cravings, regulates our emotions, protects us from cancer & dementia, staves off cold & flu, lowers our risk of stroke, diabetes & heart attack, & makes us happier, less depressed & less anxious.

So what, then, explains what Walker calls “society’s apathy towards sleep”? Why are we all so unceasingly under-slept, particularly when we know how vital sleep is?

“Firstly, increased work hours, I think people are working longer to begin with,” says Walker. “Secondly, we know that actual commute times have also increased, so people are leaving their houses earlier, they’re coming home later, & they’re working longer in between too, all of which starts to squeeze sleep in this sort of vice grip & starts to pinch it down.”

Then there are our drugs of choice: “Caffeine consumption is obviously up. Caffeine is the second most traded commodity on the surface of the planet, would you believe, after oil, which tells you everything about the state of our sleep-deprived society. If there was a commercial metric of how sleep-deprived we are, it is probably that. Caffeine keeps us awake, it makes it harder to fall asleep, we all know that, but some people might not know caffeine also prevents you from getting good, deep sleep. So someone might say to me, 'I’m just one of those people who can have a coffee after dinner & I’m fine, I fall asleep & it’s no problem'. The problem is that even if you fall asleep, the depth of your sleep won’t be as deep as if you had abstained from coffee.”

So, giving yourself a cut-off time of midday, or at the latest 2pm, for your last coffee of the day is sensible. As for our other most beloved drug, alcohol, well, Walker says we shouldn’t be drinking at all at night-time if we want to get the best possible snooze in.

“Alcohol is probably the most misunderstood of all chemicals we use for sleep,” he says. “People often say you can have a night cap, you fall asleep more quickly – it’s actually incorrect because alcohol is a type of drug that we call a sedative & unfortunately sedation is not sleep, it’s very different & it doesn’t give you the benefits of sleep. So when people say they fall asleep more quickly when they’ve had a bit of whiskey, they’re losing consciousness but they’re not falling into a natural sleep. Alcohol also fragments your sleep throughout the night so you wake up many more times & wake the next morning feeling un-refreshed & un-restored. It blocks your dream sleep or your REM sleep, which is vital for many aspects of brain & body health, particularly emotional regulation & control.”

The other things keeping us awake are light, technology & heat. Since Thomas Edison invented the light bulb, we have chased away the darkness that naturally tells us when to sleep. PC & mobile phone screens also contribute to this diminishing of darkness, which we actually need to trigger the release of the hormone melatonin, which tells the body to sleep. That, & we are setting our air-conditioners too high. Most people tend to go for about 20 degrees Celsius on their radiators, but that’s actually too hot to sleep properly. Sleep requires a little cool – something more like 18 degrees Celsius. It also requires regularity – we should be going to bed & waking up at the same time each day no matter what – but we rebel against this rule flagrantly.

Underscoring all these logistical factors is a dangerous disrespect for the act of sleeping. We tend to associate sleep with slothfulness, dismissing people who sleep eight hours or more a night as lazy, rather than sensible, as they are. We shame teenagers for sleeping in, shun night owls for their natural sleep cycles, tease habitual nappers & roll our eyes at anyone who wants to get an early night. We simply do not appreciate how important sleep is – in fact, we seem to celebrate sleep deprivation like it’s noble or remarkable in some way. It is not. It is dangerous & life-threatening.

Reading Walker’s book has shocked me into prioritizing my own sleep more. I, for one, will be trying to lock in regular bedtimes, regulating my coffee intake, working on making my office hours sensible, switching off my phone an hour before bed, & checking my room temperature & my attitude. I’d suggest you do the same. Good luck, & sweet dreams.