So there are probably many mechanisms, but one of the ones that is best understood is that we know that when you're sleep-deprived, or indeed when your sleep is disrupted by anything else like, for example, sleep apnea, there are changes that occur in terms of hormone levels of hormones that regulate our appetite and our satiety. And so even a single night of sleep deprivation can result in a dramatic increase in your calorie intake overnight.

There have been some studies done, for example, in nurses. So there was a study done that followed up nurses for 18 years, and they looked at their weight and how much they slept on a regular basis. And what they found is that those nurses that were sleeping less than about six hours a night on a regular basis, first of all, started off at the beginning of that 18-year period at a slightly higher weight. But over the course of those 18 years, they put on much more weight than other groups. So there is a very clear correlation between sleep duration, sleep quality, and weight gain. We see that, for example, in individuals who we treat with sleep apnea. So one of the treatments for sleep apnea is a mask-like device that you wear that stops your airway from closing down at night. And for some very overweight individuals, actually, when you treat their sleep apnea, they do manage to successfully lose weight, where in the past they found it absolutely impossible to do so.

Okay, so if I'm underslept, I'm more likely to eat more calories the next day. Am I also more likely to reach for foods that are high in sugar and bad for me?

Certainly some studies do suggest that. I think it's also important to say that sleep disruption or sleep deprivation has some fundamental effects, for example, on your glucose tolerance, so your insulin resistance, which of course is a particular issue for people with diabetes, but it affects us all. So if you're very sleep deprived, there are changes to the way that not only your appetite or what you're reaching for, but also how your body processes the breakdown of those foodstuffs.

Interesting. Because anecdotally, I think I can clearly say that if I'm underslept,

I'm much more likely to eat something that is high in sugar or is not good for me.

We can all testify to that, can't we? I think everybody has known that situation where they're very sleep deprived and they think, oh, well, I just need a bit of chocolate.

What's going on in the brain, though? Is it something to do with the amygdala and the prefrontal cortex, the emotional centre of our brain?

Yeah, I don't think we know. I think it's probably to do with the reward mechanisms that underlie our behaviours, that there is something about sleep deprivation that alters the rewards that we're seeking. But I don't think I can give you a clear answer on that.

You also talked about circadian rhythms. If I was a 10-year-old, what do I need to understand about the circadian rhythm? What it is, what it does, and why it's important?

Within pretty much every cell of our bodies, there is this 24-hour clock. In fact, if you take a single cell and stick it in a Petri dish, about 40% of the genes within that cell will exhibit this 24-hour cycle. That 24-hour cycle really controls pretty much every biological system within our bodies, be it how our liver works, how our heart works, how our lungs work.

There is one particular area of the brain called the suprachiasmatic nucleus that is viewed as the master clock. It's the clock that coordinates all the other clocks within our bodies. That influences not only all of these other clocks that are occurring within the cells throughout our bodies, but influences our behaviour as well. It influences, generally speaking, when we feel tired, when we want to go to bed, and when we wake up. It also influences things like when we feel most mentally alert, when we want to eat, when we want to drink, when we feel most able to cope with work, for example. Now, that circadian rhythm, that circadian clock, for most people, confers the sleep onset of somewhere between 10pm and midnight, if you're an adult, and waking up somewhere between 6am and 8am. Now, the timing of that body clock is governed by two things. It's governed by our genetics, so whether or not we are genetically predetermined to be slightly later in terms of our body clock or slightly earlier.

We see that in families where lots of people, for example, will say, you know, I've always gone to bed late and woken up late, but so has my father, so has my grandfather, etc, etc. But it's also influenced by what's happening in our environment.

About 50% of the definers of our circadian clock are governed by what's going on around us, be that in terms of when we're exposed to light, so we know that light is a very important driver of our circadian rhythm, when we're eating, when we're exercising, when we're doing a whole range of other activities. And also, one of the markers of our circadian rhythm is the secretion of melatonin. So, there's a very small gland in the centre of our brains called the pineal gland, which secretes a hormone called melatonin. That hormone tends to start being secreted in most people at around 6 o'clock in the evening. It peaks at the time that we want to go to sleep, and then it starts dropping down a few hours before we wake up. It's almost a chemical marker of our circadian rhythm. But we also know that giving people melatonin in tablet form, for example, can influence our circadian rhythm. So, there's this sort of feedback loop between our own body's secretion of melatonin and what our suprachiasmatic nucleus, our master clock, is doing. So, by giving people melatonin at particular times of the day, we can shift your circadian rhythm forward or back. So, that master clock in the brain, where is it positioned?

The suprachiasmatic nucleus is in a small area of the brain called the hypothalamus.

And is that linked to the eye? There are links from the back of the eye to the hypothalamus. So, there are some cells in the back of the eye, in the retina, that are not involved in vision, not involved in conscious vision. But what they are involved with is detecting blue light in particular, which is the part of the spectrum of light that is most important in terms of regulating our circadian clock. And there are direct links between these cells that are called retinal ganglion cells and the suprachiasmatic nucleus.

So, exposure to light, to blue light in particular, is really very important in reinforcing or adjusting our circadian rhythm. Now, of course, we live in a world whereby the seasons change, and the amount of light that we're exposed to changes. So, if we were on a set rhythm all the time that was immovable and unadjustable, then there would be times where our circadian rhythm might be at odds with our environment. So, there does need to be some slight adjustment of that circadian rhythm, and light is probably the most important adjuster.

Blue light, is that the light that comes from my smartphone?

So, blue light, obviously, the strongest source of blue light is sun. But yes, these kinds of devices, your smartphone, your iPad in front of you, a range of electronic devices also have blue light within them. So, that's why if I'm up on my phone until 1am in the morning, staring into the screen, I'm kind of tricking that sort of optic nerve, which is then impacting my master clock, and I'm telling it that it's a different time.

Yeah, so the thinking on that has changed a little bit over the last few years. So, you know, it was said that using these devices will trigger insomnia as a result of blue light.

Actually, it's likely that the amount of blue light that these devices put out is probably insufficient to do that directly. But there are two effects of using your gadget until 1am. The first is on a long-term basis, if you're doing that regularly, it will result in an adjustment of your circadian clock and push it back. So, you will want to go to bed a little bit later and wake up a little bit later, which is fine if you're self-employed or you don't have any restrictions on your time. But most of us need to be up at a certain time in the morning. And if your circadian rhythm is delayed significantly, the net effect of that is that you're going to end up sleep deprived. I mean, there's also the issue of being, you know, on Twitter or being engrossed in a movie on Netflix at 1am that is going to make you delay sleep anyway. So, there are those two effects. It's arousing and it grips your attention.

Well, what do you make of these people, me being one of them, that watch, you know, serial killer movies when we fall asleep?

Well, I think that that's only an issue if it's stopping you from falling asleep.

Because I have this argument a lot with my partner. She can't understand why I need to watch this, like, really stimulating stuff when I fall asleep. She likes quiet and I need to,

I tell myself I need to, like, listen to something. Do you see, like, variance in this kind of thing? And is there a better approach?

This comes down to an individualised approach to sleep. And that's why I'm always very reluctant to say this is the perfect night's sleep. These are the rules for sleep. You know, for example, there are some people who, for whom caffeine doesn't really influence their sleep and can have a double espresso an hour before bed and still have no problems getting off to sleep. For most of us, that's not the case. If you are somebody who can watch something very stimulating, very scary, and then switch it off and roll over and go off to sleep, then I guess that's not a problem for you. For most people, that's probably not the best thing to be doing at night. I think that long term, one of the issues is with all of these kinds of activities in bed at night before you go off to sleep, is that they weaken the psychological associations between bed and sleep. And so if you start associating bed being a place where you're mentally active, where you're engaged, then if you have an underlying predisposition to insomnia, for example, then that can sometimes set the stage for developing insomnia later on. The average person that you've treated, worked with in your clinical practice that's struggling with sleep, is at the heart of the issue just poor sleep hygiene, like you've said there. Because I've got so many friends that say to me that they struggle with their sleep. Many of them have struggled with it for years. And I doubt that there's some sort of genetic reason why this many people are struggling with sleep. So I imagine it's just some kind of behavioural reason. So I think that the genes that predispose to insomnia are pretty widespread, but obviously, you know, in pretty much all areas of medicine, there is an interaction between genetics and environment. And certainly poor sleep hygiene, and that's a horrible term,

I hate that term, but it's the term that is most widely used and understood, can certainly put in place certain aspects of behaviour that then can give rise to chronic insomnia in the long term.

So if you've got very bad chronic insomnia, then suddenly, putting good sleep hygiene in place is unlikely to fix it. But it may be that that poor sleep hygiene in the first instance gave rise or at least predisposed you to developing insomnia.

And what is poor sleep hygiene? If I wanted to be the worst possible sleeper in the world, what would I have to do?

So I think you would probably have to set up your home office in your bedroom.

Okay.

You'd have to have, you know, your TV on in your bedroom all the time.

Okay.

And be surrounded by electronic devices. Drink a lot of coffee late in the evening.

Alcohol.

Drink a little bit of alcohol. So alcohol in the short term, of course, is quite sedating.

It's a central nervous system depressant. But it does dramatically worsen the quality of your sleep and for various reasons, the direct chemical effect, the fact that you've got a full bladder, and the fact that you're probably snoring a little bit more. So alcohol is not a good thing.

You know, not having a wind down period. So, you know, gambling on the stock market until 1am, switching your laptop and then trying to go to bed.

Those kinds of things. So that's, you know, the quintessential, very, very bad sleep hygiene.

What about when I eat?

So, you know, eating is perhaps less important, but avoiding a very large carbohydrate meal, carbohydrate rich meal before you go to bed for two reasons. One is that we know that it can cause some fluctuations in terms of your blood sugar. And also, if you've got a bit of reflux, it can make that much worse.

Okay. What about sleeping in bed with somebody else?

Well, I think that for some people they find, again, this goes back to no one rule for everybody.

You know, if you've got a sleep trait termed sleep reactivity, which is where your sleep is very liable to your environment, then obviously sleeping next to somebody who's snoring loudly, or who gets up in the middle of the night two or three times to urinate can be very disruptive to your sleep. If you've got very little sleep reactivity, you may actually find it comfortable, more comfortable to sleep with somebody in the same bed as you.

I was thinking the other day, because where I've currently moved into, there's no blinds or curtains in my bedroom. And I was wondering if that might be a good thing.

Because it at least means that in terms of my circadian rhythm,

I'm waking up at the same time every day. Because I'm waking up when the sun comes up.

Yeah, but the sun comes up at different times on different days, firstly. So if you were doing that routinely, you might find yourself really rather sleep deprived in the summer months. And also, there is some emerging evidence that exposure to light at night in your sleep is not very good for you. So there was a very recent study that implied that light exposure at night increases your risk of diabetes. So it certainly is not good for the quality of your sleep. And the likelihood is that you won't wake up as soon as it's light, you'll wake up at an hour or so after it's got light, but during that hour or so, it may have had a negative impact on the quality of your sleep.

So having a dark bedroom is really part of good sleep hygiene, as it's having a quiet bedroom that is not too hot or too cold. What if you wear a sleep mask? Does that solve it? Yes, it does. I mean, I wear a sleep mask. I think it's, you know, particularly if you don't have good blackout curtains or blinds in your bedroom, using a sleep mask, particularly in the summer months, is probably very helpful indeed. Does that mean that the only light receptors we have are behind our eyes? Well, I think that there was a, there were some rumours on the internet that there were light receptors elsewhere, but certainly the only ones that we know to be of significance in terms of defining our circadian rhythm are the ones in our retinas. If you love the DRIVERS CEO brand and you watch this channel, please do me a huge favour, become part of the 15% of the viewers on this channel that have hit the subscribe button. It helps us tremendously, and the bigger the channel gets, the bigger the guests.