In this article, I’m going to tell you about the brain and the functions of learning and memory and what happens when there is sleep deprivation or lack of sleep.

Well, I would like to start with testicles. Men who sleep five hours a night have significantly smaller testicles than those who sleep seven hours or more. 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. And we see equivalent impairments in female reproductive health caused by a lack of sleep. This is the best news that I have for you today. From this point, it may only get worse.

A study regarding sleep

So let me show you the data. Here in this study, we decided to test the hypothesis that pulling the all-nighter was a good idea. So we took a group of individuals and assigned them to one of two experimental groups. One was a sleep-group and the other, a sleep-deprivation group. Now the sleep group, they’re going to get a full eight hours of slumber. But the deprivation group, we’re going to keep them awake in the laboratory, under full supervision. Then the next day, we’re going to place those participants inside an MRI scanner. Then we’re going to have them try and learn a whole list of new facts as we’re taking snapshots of brain activity. After that, we’re going to test them to see how effective that learning has been. And that’s what you’re looking at here on the vertical axis. 

stress due to lack of sleep

When you put those two groups head to head, what you find is a quite significant. 40-percent deficit in the ability of the brain to make new memories without sleep. I think 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 percent. We’ve gone on to discover what goes wrong within your brain to produce these types of learning disabilities.

The information inbox of your brain

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 you look at this structure 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. So that’s the worse that can happen if I were to take sleep away from you. But let me just come back to that control group for a second.

Do you remember those folks that got a full eight hours of sleep?

Well, we can ask a very different question: 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 brain waves 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 brain waves 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. It is important that we understand what during sleep actually transacts these memory benefits, because there are real medical and societal implications.

Let me just tell you about one area that we’ve moved this work out into, clinically, which 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 that I was just discussing.

Last year, we finally published evidence that these two things, they’re not simply co-occurring, they are significantly interrelated. It suggests that the disruption of deep sleep is an underappreciated factor that is contributing to cognitive decline or memory decline in aging, and most recently we’ve discovered, in Alzheimer’s disease as well. Now, I know this is remarkably depressing news. It’s in the mail. It’s coming at you. But there’s a potential silver lining here. 

Ways to get sleep

Unfortunately, they are blunt instruments that do not produce naturalistic sleep. Instead, 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 brain waves, not only can you amplify the size of those deep-sleep brain waves, but in doing so, we can almost double the amount of memory benefit that you get from sleep.

The question now is whether we can translate this same affordable, potentially portable piece of technology into older adults and those with dementia. Can we restore back some healthy quality of deep sleep, and in doing so, can we salvage aspects of their learning and memory function? That is my real hope now. That’s one of our moon-shot goals, as it were. 

A girl sleeping

Experiment: Daylight saving time

We’ve already spoken about sleep- loss and your reproductive system. Or I could tell you about sleep-loss and your cardiovascular system, and that all it takes is one 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-percent increase in heart attacks that following day. 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. But as a deeper dive, I want to focus on this: sleep-loss and your immune system. 

And here, I’ll introduce these delightful blue elements in the image. They are called natural killer cells, and you can think of natural killer cells almost like the secret service agents of your immune system. They are very good at identifying dangerous, unwanted elements and eliminating them. In fact, what they’re doing here is destroying a cancerous tumor mass.

Does lack of sleep causes cancer?

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 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 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, I’m being quite serious now — it is mortally unwise advice. We know this from epidemiological studies across millions of individuals.

Sleep deprivation can cause many disease

There’s a simple truth: the shorter your sleep, the shorter your life. Short sleep predicts all-cause mortality.

So here in this study, they took a group of healthy adults and they limited them to six 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 eight hours of sleep a night. And there were two 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. Now 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 many diseases. It leads to 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.

How to get good sleep?

And at this point, you may be thinking, “Oh my goodness, how do I start to get better sleep? What are you tips for good sleep?”Well, beyond avoiding the damaging and harmful impact of alcohol and caffeine on sleep, and if you’re struggling with sleep at night, avoid 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 slumber and improve the quantity and the quality of that slumber.

The second is to 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.


Sleep is a non-negotiable biological necessity. It is your life-support system, and it is Mother Nature’s best effort yet at immortality. 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. 

And with that soapbox rant over, I will simply say, good night, good luck, and above all … I do hope you sleep well. Thank you.