The next day, we placed participants from both groups inside an MRI scanner and we asked them to learn a whole list of new facts, as we were taking snapshots of brain activity. And then we tested them to see how effective that learning had been. And what we found is a quite significant - 40% - deficit in the ability of the brain to make new memories without sleep. This should be concerning, considering what we know is happening to sleep in our education populations right now. In fact, to put that in context, it would be the difference in a child acing an exam versus failing it miserably - 40%!

We’ve gone on to discover what goes wrong within your brain to produce these types of learning disabilities. There’s a structure that sits on the left and the right side of your brain, called the hippocampus. You can think of the hippocampus almost like the informational inbox of your brain. It’s very good at receiving new memory files and then holding on to them.

When we looked at the hippocampus in those people who’d had a full night of sleep, we saw lots of healthy learning-related activity. Yet in those people who were sleep-deprived, we actually couldn’t find any significant signal whatsoever.

So it’s almost as though sleep deprivation had shut down your memory inbox, and any new incoming files - they were just being bounced. You couldn’t effectively commit new experiences to memory.

What is it about the physiological quality of your sleep when you do get it that restores and enhances your memory and learning ability each and every day? By placing electrodes all over the head, what we’ve discovered is that there are big, powerful brainwaves that happen during the very deepest stages of sleep that have riding on top of them these spectacular bursts of electrical activity that we call sleep spindles.

It’s the combined quality of these deep-sleep brainwaves that acts like a file-transfer mechanism at night, shifting memories from a short-term vulnerable reservoir to a more permanent long-term storage site within the brain, and therefore protecting them, making them safe. And it is important that we understand what during sleep actually transacts these memory benefits, because there are real medical and societal implications.

One area that we’ve moved this work out into, clinically, is the context of aging and dementia. Because it’s of course no secret that, as we get older, our learning and memory abilities begin to fade and decline. But what we’ve also discovered is that a physiological signature of aging is that your sleep gets worse, especially that deep quality of sleep. And only last year, we finally published evidence that these two things, they’re not simply co-occurring, they are significantly interrelated.

The evidence suggests that the disruption of deep sleep is an underappreciated factor that is contributing to cognitive decline or memory decline in aging and in Alzheimer’s disease as well. This is remarkably depressing news. But there’s a potential silver lining here. Unlike many of the other factors that we know are associated with aging, for example changes in the physical structure of the brain, that’s fiendishly difficult to treat. But that sleep is a missing piece in the explanatory puzzle of aging and Alzheimer’s is exciting because we may be able to do something about it.

We’re actually developing a method based on this. It’s called direct-current brain stimulation. You insert a small amount of voltage into the brain, so small you typically don’t feel it, but it has a measurable impact. Now if you apply this stimulation during sleep in young, healthy adults, as if you’re sort of singing in time with those deep-sleep brainwaves, not only can we amplify the size of those deep-sleep brainwaves, but in doing so, we can almost double the amount of memory benefit that you get from sleep.

But sleep is just as essential for your body. I can tell you about sleep loss and your cardiovascular system, and that all it takes is 1 hour. Because there is a global experiment performed on 1.6 billion people across 70 countries twice a year, and it’s called daylight saving time. Now, in the spring, when we lose one hour of sleep, we see a subsequent 24% increase in heart attacks that following day. In the autumn, when we gain an hour of sleep, we see a 21% reduction in heart attacks. And you see exactly the same profile for car crashes, road traffic accidents, even suicide rates.

But as a deeper dive, I want to focus on this: sleep loss and your immune system. So, within the immune system there are these cells called natural killer cells, and you can think of them almost like the secret service agents of your immune system. They are very good at identifying dangerous, unwanted elements and eliminating them. So what you wish for is a virile set of these immune assassins at all times, and tragically, that’s what you don’t have if you’re not sleeping enough.

In this experiment, participants wouldn’t have their sleep deprived for an entire night, they’d simply have their sleep restricted to 4 hours for 1 single night, and then we were going to look to see what’s the percent reduction in immune cell activity that they suffer. And it’s not small; it’s not 10%; it’s not 20%; there was a 70% 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 of forms of cancer associated with short sleep duration 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 nighttime shift work as a probable carcinogen, because of a disruption of your sleep-wake rhythms.

So you may have heard of that old maxim that you can sleep when you’re dead. Well, 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. And if increasing your risk for the development of cancer or even Alzheimer’s disease were not sufficiently disquieting, we have since discovered that a lack of sleep will even erode the very fabric of biological life itself, your DNA genetic code.

In this study, they took a group of healthy adults and they limited them to 6 hours of sleep a night, for one week, and then they measured the change in their gene activity profile relative to when those same individuals were getting a full 8 hours of sleep a night. And there were 2 critical findings. First, a sizable and significant 711 genes were distorted in their activity, caused by a lack of sleep. The second result was that about half of those genes were actually increased in their activity. The other half were decreased.

Those genes that were switched off by a lack of sleep were genes associated with your immune system, so once again, you can see that immune deficiency. In contrast, those genes that were actually upregulated or increased by way of a lack of sleep, were genes associated with the promotion of tumors, genes associated with long-term chronic inflammation within the body, and genes associated with stress, and, as a consequence, cardiovascular disease.

There is simply no aspect of your wellness that can retreat at the sign of sleep deprivation and get away unscathed. It’s rather like a broken water pipe in your home. Sleep loss will leak down into every nook and cranny of your physiology, even tampering with the very DNA nucleic alphabet that spells out your daily health narrative.

Well, beyond avoiding the damaging and harmful impact of alcohol and caffeine on sleep, and if you’re struggling with sleep at night, avoiding naps during the day, I have two pieces of advice for you. 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 piece of advice 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 then finally, in taking a step back, then, what is the mission-critical statement here? Well, I think it may be this: sleep, unfortunately, is not an optional lifestyle luxury. Sleep is a nonnegotiable biological necessity. It is your life-support system, and it is Mother Nature’s best effort yet at immortality. And the decimation of sleep throughout industrialized nations is having a catastrophic impact on our health, our wellness, even the safety and the education of our children.

It’s a silent sleep loss epidemic, and it’s fast becoming one of the greatest public health challenges that we face in the 21st century. I believe it is now time for us to reclaim our right to a full night of sleep, and without embarrassment or that unfortunate stigma of laziness. And in doing so, we can be reunited with the most powerful elixir of life, the Swiss Army knife of health, as it were.