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Overview from TED

Sleep is your life-support system and Mother Nature's best effort yet at immortality, says sleep scientist Matt Walker. In this deep dive into the science of slumber, Walker shares the wonderfully good things that happen when you get sleep - and the alarmingly bad things that happen when you don't, for both your brain and body.

"Men who sleep five hours a night have significantly smaller testicles than those who sleep seven hours or more."

White Brick Wall
Matt Walker

Sleep Scientist | Author

Matt Walker is a Professor of Neuroscience and Psychology at the University of California, Berkeley, and Director of the Center for Human Sleep Science.



When you hear the word “sleep”, it’s unlikely that testicles are the first thing that come to mind. Until you’ve watched Matt Walker’s TED Talk, that is…

Met by reverberations of nervous laughter, Walker begins with a shocking fact:

“Men who sleep five hours a night have significantly smaller testicles than those who sleep seven hours or more.”

He continues:

“In addition, men who routinely sleep just four to five hours a night will have a level of testosterone which is that of someone 10 years their senior. So a lack of sleep will age a man by a decade in terms of that critical aspect of wellness.”


For years, working men – and women – have spoken of a lack of sleep as a badge of honour. Dubbed the “Sleepless Elite”, the likes of Thomas Edison, Benjamin Franklin, Donald Trump and, perhaps most famously, Margaret Thatcher can be counted among their ranks. Whether certain individuals are genetically exempt from requiring eight hours’ sleep is an area of ongoing research, but for the rest of us it remains as important as eating and drinking.

Matt Walker is no stranger to TED content. Following this “Sleep is Your Superpower” talk in spring 2019 (viewed more than 12 million times), he has produced a series of short videos exploring the importance of sleep, correlations with immunity and disease, and the impact of substances – such as caffeine and alcohol - on both the quantity and quality of your shut-eye. At best, his findings are alarming. At worst? Downright terrifying.


Of all the shocking facts and figures in Walker’s presentation, one in particular struck me: the impact of sleep loss on cardiovascular systems. Walker points to a global experiment performed on 1.6 billion people across 70 countries twice year. You will know it as “daylight saving time”.

Sadly, there is little “saving” taking place where the springtime change is concerned. According to Walker, that loss of just one hour of sleep results in a 24% increase in heart attacks the following day. He continues:

“In the autumn, when we gain an hour of sleep, we see a 21-percent reduction in heart attacks. Isn't that incredible? And you see exactly the same profile for car crashes, road traffic accidents, even suicide rates.”

It’s surprising that the practice of moving the clocks forward and back is still observed in the face of such damning evidence. Perhaps the expectation is that common sense should prevail – that 1.6 billion people (and counting) should go to bed one hour earlier to compensate for the time shift. But is it that simple?

Walker deems sleep to be “a non-negotiable biological necessity”, “your life-support system” and “Mother Nature’s best effort yet at immortality.” Why then, do we think pulling all-nighters is acceptable? That partying to the early hours is something to aspire to, or that getting eight hours’ sleep every night is somehow a symptom of laziness?

Perhaps part of the problem is our lack of respect for sleep - something this talk tackles quicker than you can say “don’t let the bed bugs bite…”

Referencing a second experiment, Walker shares images of “natural killer cells” – the secret service agents of your immune system that identify dangerous, unwanted elements (such as cancerous masses) and eliminate them:

“So here in this experiment, you're not going to have your sleep deprived for an entire night, you're simply going to have your sleep restricted to four hours for one single night, and then we're going to look to see what's the percent reduction in immune cell activity that you suffer. And it's not small -- it's not 10 percent, it's not 20 percent. There was a 70-percent drop in natural killer cell activity. That's a concerning state of immune deficiency, and you can perhaps understand why we're now finding significant links between short sleep duration and your risk for the development of numerous forms of cancer.

“Currently, that list includes cancer of the bowel, cancer of the prostate and cancer of the breast. In fact, the link between a lack of sleep and cancer is now so strong that the World Health Organization has classified any form of night-time shift work as a probable carcinogen, because of a disruption of your sleep-wake rhythms.”

He adds:

“So, you may have heard of that old maxim that you can sleep when you're dead. Well, I'm being quite serious now - it is mortally unwise advice. We know this from epidemiological studies across millions of individuals. There's a simple truth: the shorter your sleep, the shorter your life. Short sleep predicts all-cause mortality.”

Partying all night doesn’t sound so fun now, does it?


Many people – myself included – struggle to drift off at night. During stressful periods, I fall victim to bouts of insomnia; I feel mentally and physically exhausted but am unable to switch off. Walker recommends – as common-sense dictates – to reduce (or cut out altogether) stimulants such as alcohol and caffeine, and to avoid naps during the daytime. But he also offers two pieces of advice which are often overlooked:

“The first is regularity. Go to bed at the same time, wake up at the same time, no matter whether it's the weekday or the weekend. Regularity is king, and it will anchor your sleep and improve the quantity and the quality of that sleep.

“The second is keep it cool. Your body needs to drop its core temperature by about two to three degrees Fahrenheit to initiate sleep and then to stay asleep, and it's the reason you will always find it easier to fall asleep in a room that's too cold than too hot. So, aim for a bedroom temperature of around 65 degrees, or about 18 degrees Celsius. That's going to be optimal for the sleep of most people.”

And if that doesn’t work?

“If you are staying in bed awake for too long, you should get out of bed and go to a different room and do something different. The reason is because your brain will very quickly associate your bedroom with the place of wakefulness, and you need to break that association. So only return to bed when you are sleepy, and that way you will relearn the association that you once had, which is your bed is the place of sleep. So, the analogy would be, you'd never sit at the dinner table, waiting to get hungry, so why would you lie in bed, waiting to get sleepy?”

I love a good analogy, and especially one that shines a light on illogical human behaviour. In no other circumstance would you “wait” in this manner, so why should bedtime be any different? By following Walker’s first piece of advice – regular sleeping times – your mind and body should become accustomed to the pattern, transforming an unwelcome nightly deliberation (“am I tired yet?”) into a subconscious habit.

For me, the biggest wake-up call from Walker’s talk came from a single sentence: “Sleep is not an optional lifestyle luxury.

Sleep isn’t something we should “fit in” to our busy schedule. We shouldn’t “survive” on four or five hours a night. If we need eight hours’ sleep to thrive, then we owe it to ourselves to plan our time accordingly. Our lives depend on it, after all…

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