Why great sleep does more good than diet or exercise

Matthew Walker, a world expert on sleep, explains how losing just an hour’s shut-eye can cause illness and disease

DO YOU think you got enough sleep this past week? Can you recall the last time you woke up without an alarm clock feeling refreshed and not in desperate need of caffeine?

If the answer to either of these questions is ‘No’, you are not alone. Two-thirds of adults throughout all developed nations fail to get the recommended eight hours of sleep a night.

I doubt you are surprised by this fact — but you may be surprised by the consequences.

Routinely sleeping less than six or seven hours a night demolishes your immune system and more than doubles your risk of cancer.

Insufficient sleep is a key lifestyle factor determining whether or not you will develop Alzheimer’s disease. Even moderate reductions in sleep for just one week disrupts blood

MATTHEW WALKER is one of the world’s leading experts on sleep. He was born in Liverpool and graduated in neuroscience and neurophysiology in the UK before going on to become a professor at Harvard University, where he became fascinated by the science of why we sleep. He moved on to the University of California, Berkeley, where he is currently professor of neuroscience and psychology, and director of the Centre for Human Sleep Science.

sugar levels so profoundly that you would be classified as pre-diabetic.

Short sleeping increases the likelihood of your coronary arteries becoming blocked and brittle, setting you on a path towards cardiovascular disease, stroke and congestive heart failure.

Sleep disruption further contributes to all major psychiatric conditions, including depression and anxiety. It can even lead to suicide.

Perhaps you have also noticed a desire to eat more when you’re tired? This is no coincidence. Too little sleep swells concentrations of a hormone that makes you feel hungry, while suppressing a companion hormone that signals food satisfaction.

Despite being full, you still want to eat more. It’s a proven recipe for weight gain in sleep-deficient adults and children alike.

When you add up all of the above health consequences, a proven link becomes easier to accept — the shorter your sleep, the shorter your life span. The old maxim ‘I’ll sleep when I’m dead’ is therefore rather unfortunate.

And it is no coincidence that countries where sleep time has declined most dramatically over the past century, such as Ireland, the US, the UK, Japan, South Korea, and several other nations in western Europe, are also those suffering the greatest increase in rates of the aforementioned physical diseases and mental disorders.

Scientists such as myself have even started lobbying doctors to start ‘prescribing’ sleep.

As medical advice goes, it’s perhaps the most painless and enjoyable to follow.

There does not seem to be one major organ within the body, or process within the brain, that isn’t enhanced by sleep (and impaired when we do not get enough).

That we receive such a bounty of health benefits each night should not be surprising.

After all, we are awake for twothirds of our lives, and we don’t just achieve one useful thing during that time, but rather myriad accomplishments that promote our well-being and survival.

Why, then, would we expect sleep — and the 25 to 30 years, on average, it takes from our lives — to offer one function only?

Sleep dispenses a multitude of health-ensuring benefits — and they’re yours to pick up as a repeat prescription every 24 hours, should you choose.

It enriches a diversity of functions within the brain, including our ability to learn, memorise and make logical decisions.

Sleep also recalibrates our emotional brain circuits, allowing us to navigate the social and psychological challenges of the next day with cool-headed composure.

WE are even beginning to understand the most impervious of all conscious experiences: the dream.

Dreaming provides a unique set of benefits, including soothing painful memories and inspiring creativity, as I will be explaining next week.

Downstairs in the body, sleep restocks the armoury of our immune system, helping to fight malignancy, preventing infection and warding off all manner of illnesses.

Sleep also reforms the body’s metabolic state by fine-tuning the balance of insulin and circulating glucose.

It regulates our appetite, helping to control body weight by encouraging healthy food selection rather than impulsive choices.

It is also needed to maintain a flourishing microbiome within your gut, where so much of our nutritional health begins.

Adequate sleep is also closely tied to the fitness of our cardiovascular system, lowering blood pressure while keeping our hearts in fine condition. It is difficult to imagine any other state that offers a more powerful redressing of physical and mental health.

I love sleep (and not just my own, although I do give myself a nonnegotiable eight-hour opportunity for it each night).

I want to discover all that remains unknown about it, and I hope to find any and all methods for reuniting humanity with the sleep it so desperately needs. I was once fond of saying: ‘Sleep is the third pillar of good health, alongside diet and exercise.’

I have since changed my tune. Sleep is more than a pillar — it is the foundation on which the other two health bastions sit.

A balanced diet and exercise are vital, yes. But we now see sleep as the pre-eminent force in this health trinity. The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise.

Take away the bedrock of sleep, or weaken it just a little, and careful eating or physical exercise become less than effective.

Recall the last time you had the flu. Miserable, wasn’t it? Runny nose, aching bones, sore throat, heavy cough and a total lack of energy. You probably just wanted to curl up in bed and sleep. As well you should.

Your body is trying to sleep itself well. Sleep fights against infection and sickness by deploying weaponry from your immune arsenal and cladding you with protection.

When you do fall ill, the immune system actively stimulates the sleep system, demanding more bed rest to help reinforce the war effort.

Reduce sleep for even a single night, and that invisible suit of immune armour is rudely stripped from your body.

To investigate this, my colleague Dr Aric Prather at the University of California, San Francisco, measured the sleep of 164 healthy men and women for a week.

He then quarantined them, and proceeded to squirt a good dose (or rather a live culture) of rhinovirus, which causes the common cold, straight up their noses.

Dr Prather then kept them in the laboratory for the following week,

monitoring them intensely.

There was a clear, linear relationship with infection rate and sleep: the less sleep an individual was getting in the week before facing the active common cold virus, the more likely it was that they would catch a cold.

In those sleeping five hours on average, the infection rate was almost 50%.

In those sleeping seven hours or more a night, the infection rate was just 18%.

Infectious illnesses, such as influenza and pneumonia, are among the leading causes of death in developed countries.

Doctors and governments would therefore do well to stress the importance of getting sufficient sleep during the flu season.

Perhaps you are the sort of responsible person who gets a flu jab each year, boosting your own resilience while adding strength to the immunity of the herd — your community.

However, that flu jab is only effective if your body actually reacts to it by generating antibodies. A remarkable discovery in 2002 demonstrated that sleep profoundly impacts your response to a standard flu vaccine.

In the study, healthy young adults were separated into two groups. One had their sleep restricted to four hours a night for six nights, and the other group got between seven-and-a-half and eight-and-ahalf hours in bed each night. Everyone was then given a flu jab. In the days afterwards, researchers took blood samples to determine how effective each person was in generating an antibody response, working out whether or not the vaccination was a success.

Those participants who had the greater amount of sleep generated a powerful antibody reaction. This reflects a very robust, healthy immune system.

In contrast, those in the sleep-restricted group produced less than 50% of the immune reaction that their well-slept counterparts did.

Similar consequences of too little sleep have since been reported for the hepatitis A and B vaccines.

Perhaps the sleep-deprived group could still go on to produce a more resilient immune reaction if only they were given enough sleep recovery time? It’s a nice idea, but a false one.

Even if someone is allowed two or three weeks of recovery sleep to get over the effects of one week of short sleeping, they never go on to develop a full immune reaction to the flu jab.

In fact, certain immune cells are still diminished up to a year after just a minor, short amount of sleep restriction.

It doesn’t require many nights of short sleeping before the body is rendered immunologically weak — and here the issue of cancer becomes relevant.

Natural killer cells are an elite and powerful squadron within the ranks of your immune system.

Think of them as the secret service agents of your body, whose job it is to identify dangerous foreign elements and eliminate them — 007 types, if you will.

ONE such foreign entity that natural killer cells will target are cancerous tumour cells. Natural killer cells will effectively punch a hole in the outer surface of these cells and inject a protein that can destroy the malignancy.

What you want, therefore, is a virile set of these James Bond-like immune cells at all times.

And that is precisely what you don’t have when you sleep too little.

Dr Michael Irwin, at the University of California, Los Angeles, has carried out landmark studies revealing just how quickly and comprehensively a brief spell of short sleep can affect your cancerfighting immune cells.

Examining healthy young men, Dr Irwin demonstrated that a single night of four hours of sleep — such as going to bed at 3am and waking up at 7am — swept away 70% of the natural killer cells circulating in the immune system, relative to a night of a full eight hours of sleep.

That is a dramatic state of immune deficiency to find yourself facing after essentially one ‘bad night’ of sleep. You could well imagine the enfeebled state of your cancer-fighting immune armoury after a week of short sleep, let alone months or even years.

Well, we don’t have to imagine. A number of prominent epidemiological studies have reported that night-time shift work, and the disruption to circadian rhythms and sleep that it causes, considerably ups your odds of developing many forms of cancer.

These include breast cancer, prostate cancer, endometrial cancer and colon cancer.

As if that were not enough, a recent study by Dr David Gozal, from the University of Chicago, showed that sleep-deprived mice suffered a 200% increase in the speed and size of cancer growth, relative to those mice who were well-rested.

Worse, when Dr Gozal performed postmortem examinations on the mice, he discovered that the tumours were far more aggressive in those who were sleep-deficient. Their cancer had metastasised, spreading to surrounding organs, tissue and bone.

Indeed, the scientific evidence linking sleep disruption and cancer is now so damning that the World Health Organisation has officially classified night-time shift work as a ‘probable carcinogen’.

ADAPTED from Why We Sleep: The New Science Of Sleep And Dreams by Matthew Walker, published by Penguin Books at €14. © Matthew Walker 2018.)