How to beat the winter blues: Light and seasonal affective disorder

Winter is almost here. Temperatures are dropping, clouds are descending, and the clocks have changed. 

Many of you might be worrying that the Winter Blues are on their way, but perhaps they don’t need to be? Perhaps we can work with our natural, biological rhythms to fend off this blue phase.

After listening to this episode, you’ll be armed with solid advice that will help you weather winter with a smile, maintaining good health and good mood until the warmth returns.

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Have feedback or a topic you'd like us to cover? Let us know here.

Episode transcripts are available here.

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Transcript

Jonathan Wolf: Deborah, thank you so much for joining me today.

Prof Debra Skene: Pleasure, hello.

Jonathan Wolf: So we have a tradition here at ZOE, where we always start with a quick-fire round of questions from our listeners, and we have some very strict rules. We ask you to say yes or no or, if you have to, a one-sentence answer. Are you willing to give it a go?

Prof Debra Skene: Sure.

Jonathan Wolf: Can messing with your body clock lead to weight gain?

Prof Debra Skene: Yes.

Jonathan Wolf: Does when you eat influence your circadian rhythms?

Prof Debra Skene: Yes, we believe that as well. I think the timing of meals is very important.

Jonathan Wolf: Can the color of light influence our sleep-wake cycle?

Prof Debra Skene: Indeed, yes. Some colors are more effective than others.

Jonathan Wolf: Can light boxes help people keep their circadian rhythms on track?

Prof Debra Skene: I think so, as well.

Jonathan Wolf: What's the most surprising thing that you've learned about circadian rhythms in your 25 years of research?

Prof Debra Skene: Probably that dim light has an effect. I always thought it was just bright light, daylight having an effect on your body clocks, but even dim light has an effect on the clock.

Jonathan Wolf: So this is a big topic, to kick things off, let's go back right to basics. 

What are circadian rhythms and why do they matter for health?

Prof Debra Skene: It's more what are biological clocks? We have them all over our body, and it's critical that these clocks are synchronized with our life on Earth. 

For us as people living on Earth, we've got this critical light-dark cycle that happens every 24 hours because of the Earth's rotation. What we need to do to stay in synchrony with this, is that we have these biological clocks that are able to respond to the light-dark cycle and in unison together would give you good health.

Jonathan Wolf: Can you help me to understand a bit more what a biological clock is that's in me?

Prof Debra Skene: Well, the first one that was discovered, the sort of master clock, so to speak, is in the hypothalamus, so within your brain. And it has a direct pathway from that clock in your brain, to your eyes. 

So again, the light-dark cycle can enter your eyes and go down this nerve pathway to this master clock in your hypothalamus. 

And we know it's a clock because you can literally, not in people, but it can be taken out of animal bodies and put into a dish, and we can see the electrical activity of this clock oscillating. So it's a self-oscillating independent clock that can literally tick in a dish.

Jonathan Wolf: It actually, literally is a clock going "tick-tock, tick-tock" in my brain right now?

Prof Debra Skene: Yeah. It has a 24-hour rhythm, so it'll have a peak and a trough that takes about 24 hours to complete. So it is a self-sustaining oscillator, and that's in the brain, and that's what we call our master clock or our conductor of all these clocks. 

Because more recently, we've discovered that there are clocks throughout the body, particularly in areas that are metabolized. So we have a clock in the liver, a clock in the pancreas, a clock in muscles, in skin, and in adipose tissue. 

It's all these clocks all around our body that need to all tick in time together. And this all-synchronized clockwork needs to be synchronized to our outside world.

Jonathan Wolf: Why do we need to have these body clocks inside us?

Prof Debra Skene: The real reason we have clocks is to anticipate our next move. So they act as timekeepers, because they're clocks, but they're telling us when to wake up, when it's appropriate to sleep, when we should eat, when we should not eat. 

They will anticipate spring and summer, daytime, nighttime. So with the clocks, our bodies can tell the rest of our body, it's two hours before you should be going to sleep.

Jonathan Wolf: Could you give me an example maybe of something that happens in my body as a consequence of this clock?

Prof Debra Skene: Yes. Well, I think sleep timing. Because for example, in the evening we have a hormone in our body called melatonin that's naturally produced every night. And this begins before you sleep. 

It is released into our body and it's preparing our body to get used to the idea that you're going to perhaps and should be sleeping about two hours later. So it anticipates sleep time. 

On the other end, we have cortisol, which is another hormone, and this anticipates wake. So we get the increase in cortisol in the early morning hours before we wake up. 

The clocks are used to prepare yourself for the events of the day.

Jonathan Wolf: Help me to understand a bit more the waking up, because in my experience, I tend to just go from being asleep to being awake. 

So what does that mean that my body is preparing to be awake?

Prof Debra Skene: Right. Well, obviously when you wake up, you need energy supplies. You need to have glucose, you need to be able to cope. So cortisol is an important hormone here. 

It also involves increasing the amount of sugar or glucose in your blood. So you have processes that prepare yourself for this wake up so you're ready to get up, to cope.

Jonathan Wolf: So there's a bunch of things that are going on inside my body half an hour before I wake up that I'm not even aware of. I feel like I'm blissfully asleep. But actually my body's already starting to sort of warm myself up to get up and hit the day.

Prof Debra Skene: That's absolutely correct, yes.

Jonathan Wolf: Why do we need to have more than one body clock? It sounded like you're saying they're almost everywhere.

Prof Debra Skene: They're called peripheral clocks in our language because they're outside of the brain. But when these peripheral clocks were first identified, of course it complicated things because we didn't want to know that it's a lot more complicated than we'd originally thought.

Because then the question becomes, how do these clocks communicate with each other? Is it via a hormonal signal? Is it via a nerve pathway? Is it via metabolites? So people are still studying that.

But I guess it makes sense, because let's just take the glucose example. If we need to be prepared with glucose ready for waking up, then somehow our brain needs to be able to talk to the liver and to the pancreas and other adipose tissue, different processes that are involved in glucose balance. 

That information needs to go from the brain to these clocks, so that they are ready as well. We don't want our brain waking up and the rest of our body clocks or the rest of our organs still fast asleep in bed.

Jonathan Wolf: Makes sense. 

So all these different parts of my body have different things they're doing during the day and they need to know in advance. They can't just be told at the moment. They all sort of need this warming up that you're describing, whether it's for wake or sleep. 

And interestingly, there's not just this one central clock that's sort of running on local clocks for reasons we understand, or that's just how it is?

Prof Debra Skene: No, I think it makes absolute sense now that we know they're all there. It just makes the study of them a lot more difficult. 

For example, we study shift workers or people who travel across time zones, and you've heard of jet lag because of course we are moving very quickly, too quickly, from one time zone to the other. And we have sleep problems while we adapt. 

But of course the other thing people spoke about quite a long time ago was gut lag. You know that your toilet function, so to speak, also delays for a while or advances. They're mismatched in your new time zone and it takes a while for that to also move. 

But now we've got the idea that maybe different clocks adapt at different speeds. So this makes it harder. Maybe your heart clock takes five hours to adapt, whereas your liver clock might take eight hours to adapt. 

So then we've got more of a mismatch between the different clocks. And why that's important is because we believe that if there is a mismatch between different clocks, this isn't good for your health. This isn't optimizing function.

Anyone who knows anything about clockwork and how even normal mechanical clocks work, everything needs to work together to be the most efficient.

Jonathan Wolf: Got it. So you could have a situation where your brain is sort of on one time zone, my gut is on another, and my heart is on a third. And therefore they're sort of pulling against each other. 

Whereas I think, if I understand right, you're saying we sort of evolved so that all nicely lined up and they all know, "Oh, it's 5:00 in the morning. Jonathan's going to get up in two hours, start doing this," or "It's 8:00 PM. Jonathan's not going to have any more food."

Prof Debra Skene: Yeah.

Jonathan Wolf: I understand that light plays a very important role in sort of somehow setting the clock. Could you help us to understand that?

Prof Debra Skene: Well, it's because we evolved to live on Earth, and the most reliable environmental signal for an organism to respond to would be the light-dark cycle. 

Let's look at it the other way. It's not weather, because weather can change. Photo period, meaning the length of the day and the length of the night, is a consistent, regular event. And so it would make sense that animals would develop a way of using the signal to track the environment. 

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So it isn't weather and it's not temperature because that's too variable. It's not humidity. So photo period is the key way that all organisms, all mammals, insects, plants, algae, clocks were first discovered in algae, all respond and are able to use this light-dark cycle to stay in synchrony with life on Earth.

Jonathan Wolf: So this clock is something really fundamental. You're saying it goes all the way back to algae?

Prof Debra Skene: Yes, absolutely. It's critical that we have clocks so that the algae knows what to do during the daylight and it knows what to do at night. 

So you'll have these periods of activity and periods of rest that need to be synchronized to the environment.

Jonathan Wolf: That's interesting. Even before we were animals, just when we were single-cell creatures, something knowing that it's daylight or not has this big effect on whether you need to photosynthesize or, I guess for many, many hundreds of millions of years, whether you need to run away from a dinosaur or whatever. 

This is the profound reason why this is central across all our cells.

Prof Debra Skene: It's to optimize performance and to anticipate events. And this is about survival. 

Let's take rodents; they are nocturnal animals. Now, if they didn't have a clock telling them what time of day it is and that they should go into their burrows in the day, they might be picked out by those birds flying around in the day. 

So it's very important that we all have clocks to know when we are safe to sleep and when we should be active and eat.

Jonathan Wolf: Could you talk a bit about how light is setting those clocks?

Prof Debra Skene: Yeah. Well this is another surprising thing that I think we all discovered, and that is that eyes and light isn't just to see. 

We call these non-visual effects, it's not the perfect word. We haven't found a good word for these effects, but they do not involve vision. 

And we now know all the pathways, and the photoreceptors, and the pigments that are involved in this process. It's all happened in the last 25 years, a very exciting time. 

What we now know is how light that we see when we're outside or that I'm seeing looking at you, how it affects my body, how it can affect your mood, how it can affect how alert you feel, your reaction time, your performance. 

So it has effects that are nothing to do with vision, different pathways. And one of these pathways is the critical one in our field that goes straight from our eyes directly to this master clock in the hypothalamus. 

This was one of the first great discoveries showing how light would work to send the signal to entrain. We use the word entrainment or synchronizing our clocks to the outside environment.

Jonathan Wolf: So there's a link directly from my eye to this master clock telling it, "Okay, this is the morning," or, "This is the night." 

Prof Debra Skene: Yes. 

Jonathan Wolf: Is it only light that keeps my natural rhythms on track?

Prof Debra Skene: Well, that's been a big debate. 

So to get to that, we were studying blind people, totally blind people, in some cases where both their eyes have been removed. So we now know the pathway from light to the master clock is disrupted, gone. 

And then we are able to answer the question, "Well, what about all these other non-light cues, non-photic cues?" So you might say food or social habits. 

What we found was that if you didn't have the light-dark cycle, if you were totally blind, even with very strong social cues—because blind people, they rely more on social cues than visual people, as you can imagine—because they don't see. 

So they might have dogs, they certainly had families, they were working, so they had alarm clocks. So they had a lot of cues telling them what time of day it is. But they still continued to be desynchronized from their environment. 

We call it free running because their body clock goes at its natural periodicity. So we all have these clocks, and they all have different speeds. For the blind people, their clock continued on their own speed, and that was even with all these social cues. 

So the light is critical, and we think the most important, based on these studies in blind people.

Jonathan Wolf: So Debra, what happens if our lifestyle isn't aligned with this sort of natural body clock, this circadian rhythm? What happens to our body and our health?

Prof Debra Skene: We would all, as a field, say that this isn't good for your health. But our challenge is to try and have more detail. 

It's easy for me to say any mismatch of the clocks in our body and any mismatch between the clocks and the environment isn't good. But probably the epidemiology evidence from shift workers gives us some idea. 

Because doing night shift work is a sort of test case for really changing your activities. You delay your sleep-wake cycle, you change your eating times, you change when you are active and when you're lying down and everything. So everything is shifted. That's why we call it shift work, and it's not good for your health. 

All the epidemiology is telling us that doing shift work increases your risk of Type 2 diabetes, cardiovascular disease, and cancer. And so this mismatch of your clocks and the environment are somehow getting to a point where you increase your risk of fairly major diseases.

Jonathan Wolf: I'm a bit shocked to hear that it could even increase your risk of something like cancer, which I never would've thought could be associated with my body clock. 

I know sometimes scientists say they see this, but these are tiny changes that aren't really relevant to normal people. Are these important differences in my risk of the things you're describing?

Prof Debra Skene: There are a lot of studies now. In fact, cancer was one of the first diseases to be linked and associated with night shift work. 

This was the night shift work study in the U.S. done by colleagues in the U.S. and in Austria. And it was surprising, but many, many more studies have shown this increased risk.

Jonathan Wolf: Could you explain to me in simple terms why working at night for a shift might increase my risk of heart disease or cancer?

Prof Debra Skene: Okay. The first culprit that was produced when we talked about the risk of shift work was light at night. Because now you're in a factory, or even if you are working a night shift as a nurse, you're awake and you're getting light at night. 

So there were big hypotheses about maybe it's the light at night, but again, a lot of counterarguments. So that was the first thing. 

The next thing is, you're definitely eating at the wrong time. Now, one of the major functions of the biological clocks that we've been talking about is to partition your food and energy storage and utilization between the day and night. 

Now we are diurnal, so we need to be sure that all our metabolic processes are in tune to process the food that we eat during the day. And of course, when we sleep, our body is tuned to fast, and different, other processes kick in. 

So our clock is using this energy for activity after eating and storage at night. It's critical that that is linked to the day and night. 

Now, the minute you do shift work, you're in a situation where you're eating at night and your body, especially on the first night of shift work, your body is not at the right time to eat. And there've been good studies showing that how you process the food and your postprandial responses, so your after-meal responses to food, are delayed and exaggerated. 

For example, triglycerides: if you eat the same food at lunchtime and the same food at midnight, you'll have much higher levels of triglycerides at night.

Jonathan Wolf: And these are like the fats in your body.

Prof Debra Skene: These are the fats in your blood. You don't want this at night compared to the day. 

These were very early studies done by my mentor at Surrey, where we showed that you definitely metabolize food differently. 

And if this then is chronic, so this isn't just one night of night shift, you're doing shift work, or you're doing some day work and then some night work and your clocks are mismatched, then of course this would compromise your metabolism and compromise your health.

Jonathan Wolf: And Debra, I just want to make sure I've got that, you're saying that one of the biggest purposes of this biological clock is actually to separate the times when you're eating and the times when you're not, so that your body is sort of prepared to deal with the influx of everything that comes from the food and then have a period when you are not.

Prof Debra Skene: When you're fasting.

Jonathan Wolf: And that therefore if you are eating suddenly, in the middle of the night when I'm not expecting it, actually your body isn't prepared. And that has some quite big negative health impacts?

Prof Debra Skene: Yes. So then over time, because let's say this increase in fats at night based on the food you eat, if that accumulates over time, this could be one of the explanations. 

Once we knew the epidemiology showing this increased risk of these disorders, particularly metabolic disorders, cardiovascular problems, and cancer, people have really tried to go, "Well, what is the contributing factor?".

And so you get all these diagrams of light at night, eating food at night, mismatch of clocks, et cetera, so that it all then funnels down into, "Maybe this is increasing the risk,".

But as I say, the precise mechanisms are not known. And what's the hierarchy of these things? Is it because you've shifted your sleep-wake timing? Is that the thing that's the most disruptive for disease? Or is it the fact that you've shifted your feeding/fasting, for example? 

So we don't know that yet. If we know that, then we can start giving advice to shift workers and advice to people who employ shift workers.

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Jonathan Wolf: You're saying the thing that is causing most of the problem, it's not that I might be awake during the night and not seeing as much sunlight. It's the fact that my body clock is out of line with how I'm living.

If I was going to live in a cave for a month, I'm not having the same risk because I am sort of shifting between day and nighttime and my body clock moving around.

Prof Debra Skene: Living in a cave for a month is pretty healthy because you would be just going to your own time. So you would then be living according to your body clock timing. And this, in theory, is the most healthy thing to do. 

The problem we have is that we have a social clock that's set on our wrists here. Chronobiologists don't wear watches because we don't need a social clock to tell us what the time is; we've got our body clocks. 

But anyway, that social clock is telling you, "Please wake up. Please go to work, please go to school." And this can be in conflict with our body clock. And this is where we get this thing of the speeds of people's clocks. 

Now we get clocks that are slow and we get clocks that are fast, and people who have slow clocks are more evening types or owls, you know, late types. And people who have fast clocks are more morning types or what we call larks. And they all have to fit into this sort of nine-to-five program that we have. 

So some people are really living against their biological clock system. If you're a late type and you're being forced to wake up at six o'clock in the morning to go to work, this is a big jar and a mismatch that does eventually have some health consequences.

Jonathan Wolf: I'm a bit of a late-night person, not very late, but definitely find it quite easy to stay up, find it quite hard to pull myself out of bed early, even if I'm not on something else. Maybe that's just a sign of sort of moral weakness. 

Is this real?

Prof Debra Skene: Yes. This is absolutely real and in fact, people who are late types, or at least people who study late types, it's in the biology as well. 

So we can measure the melatonin rhythm and that is delayed or later in late types. So it's not something you can say in a questionnaire. There's actually physical hormones. Your melatonin in a late type would only start much later in the evening than an early type. 

So they're markers of a thing that you can't subjectively argue.

Jonathan Wolf: And will I be healthier if I live in line with my early or late type, rather than just arbitrarily saying, you know, "Everyone should go to bed at 10:00 PM?"

Prof Debra Skene: Yeah. When we say everyone should go to bed at a certain time, that isn't a rule that we can adopt when we talk about chronobiology or the study of biological clocks, which is what chronobiology is.

Because everything depends on the timing of your body clock. So the advice is to hopefully, if you could, naturally wake up at the time that is your preferred wake-up time, rather than using an alarm clock. 

And you'll know that most people spend the weekday, let's talk about most ordinary people, they spend the weekday using alarm clocks to wake up, and then on weekends, the alarms are switched off and everybody sleeps a little later. 

It's that difference between your weekday working day and your free day, that difference, Till Roenneberg has called social jet lag because it's a sort of jet lag. It can be up to one or two hours difference. 

More social jet lag has been associated with increased body weight. It affects your performance and mood as well. 

So there's more and more evidence where people study this mismatch between our working day and our normal day. The bigger the mismatch, the more your risk is, the bigger that difference is.

Jonathan Wolf: So let's say it's two hours. Let's say I wake up at 7:00 AM during the week and at the weekends I wake up at nine. I'm at risk of putting on more weight?

Prof Debra Skene: You are. That's definitely published.

Jonathan Wolf: Wow. That's extraordinary.

Prof Debra Skene: For example, during COVID, that social jet lag seemed to get less because people didn't have to get up, get the school bus, or go to school or go to work. And so people would've slept a little later. And so that gap between the working day and the free day was reduced.

Jonathan Wolf: That's really interesting. I definitely shifted my sleep because suddenly I didn't need to commute.

Prof Debra Skene: You know, in America especially, they have enormous commute times getting to work and things. And if you can cut that out and use it to sleep, that would be a good health message.

Jonathan Wolf: I'd love to switch now to what's going on as we're going into winter. 

So, clearly you've already told me that this light is critical for setting my central clock, and we all know that the amount of sunlight is now shrinking, particularly those of us who are fairly northern. 

Could you help me to understand what's going on as we're going into winter and this amount of light is changing?

Prof Debra Skene: Yeah. The winter-summer is a phenomenon of the Earth's orbit around the sun and the tilt. So we all understand why seasons exist and the higher your latitude, the bigger the photo period differences are. 

So it's something that is what we live with and we adapt to that. Our body clocks every day, they see light so they know they are tracking time of year as well as time of day. 

I can't say that with as much confidence in humans as I can in seasonal breeders or animals, because of course you can so clearly see their seasonality. You know, some animals change the color of their coats, they get fatter, they are breeding, and we know how the photo period, the light-dark cycle, we know how that affects and changes all of these coat growth and reproduction, et cetera. 

So it's a beautiful story and we know it. The question that we have, do humans have seasonality? That's one still outstanding question that we are all trying to study.

Jonathan Wolf: Do we have seasonality?

Prof Debra Skene: Well, we certainly have seasonality in, for example, the incidence of diseases. 

No better disease to talk about than seasonal affective disorder, or SAD, as they've coined it, like winter depression. So psychiatric diseases also have different incidences across the year, even metabolic syndrome, cardiovascular disease, infectious diseases, hugely peaking, as you'd imagine, in autumn and winter. So we have seasonality in the incidence of diseases. 

Do we have seasonality in our hormones and in our metabolites and in our response to pathogens, et cetera? So these are questions that we don't fully know the answer to.

Jonathan Wolf: As we're going into the winter, what do we know is happening to our body clocks and how might that affect us?

Prof Debra Skene: Right. So it's getting darker at every level of the day. So dawn, noon, and dusk, the light levels are lower across the board and there's less blue. 

We know that it's the blue light that is more effective than red light. We believe that the biological clocks have a tendency to get later, so we wake up later. There's less light around. 

The jury's still out about sleep duration, winter versus summer. You never do these studies on the same people. 

It's very difficult to do these studies on the same people, you can imagine. We've tried. We design the study, we want someone to come back into the lab or we want to see them at every season or every month. It's a lot on the volunteers, the recruitment's bad, people drop out. 

So normally they just take people in the winter versus people in the summer, and they're different people. And then we've got studies happening in Scandinavia, which is 70 degrees north. We've got our studies here in Guilford, 50 degrees north, so that is changing as well. 

The biggest problem is we have so changed our environment. So none of us are really living in true summer and then true winter because we have artificial light at night in the winter. We use lights more in the evening because we've got darker evenings. We have central heating, so we are not exposing ourselves to the darkness of winter as we would've done, like Eskimos. 

So we've really changed our modern environment to the point that maybe the inherent seasonality that we probably have is lost because it's so blocked out by all our things that we change in our environment.

Jonathan Wolf: How does this reduction in light affect us? 

Because I think I know that I'm going into the winter and I just feel more depressed about it. Not to the extent of having depression, but I definitely feel that. I feel this is pretty common. I suspect most listeners thinking about this are not chirping up.

And it's not only, I think, about it being colder; it feels like that reduction in light itself is somehow having some effect. Is there anything real there?

Prof Debra Skene: Very real. This is really where we have strong evidence. Seasonal Affective Disorder (SAD), that's in about 1% to 10% of the population, but it depends on the latitude you live at. 

So of course, the higher latitudes, Scotland, Aberdeen, the incidence would be greater than in South Africa where I'm from, because the higher the latitude, the less light that you're having. And that is the sort of what we'd call the clinical condition of SAD.

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But the sub-syndromal, so just under, there's a lot of people in that area where exactly like you say, you feel lethargic, a bit more depressed, you eat more carbohydrates.

And it's directly related to light, because when people are given a light box, a box that you can put on a desk and look at in the morning after you've woken up, this is effective. 

There are very many studies showing the effectiveness of light therapy for seasonal affective disorder. We know it's light, it's a direct effect of light.

Jonathan Wolf: And the impact you would expect to see is just to affect your mood, or does it affect other things? 

You mentioned before about the impact on maybe your cravings and weight gain and things like this?

Prof Debra Skene: People who have Seasonal Affective Disorder haven't been shown to have any problems with their biological clocks. So this mood disorder that they have is related to the lack of light. So this is a direct effect of light. 

We talked already about how light through the eyes has a direct effect on a lot of brain areas, so it's likely a direct effect on mood areas in the brain to improve mood.

Jonathan Wolf: And Debra, I know you've studied a lot the effects of particular colors of light, and I understand blue light in particular. Why does the color of light matter?

Prof Debra Skene: Ah, yes. Well, that was exactly our question 25 years ago, when we knew the brighter the light, the more effect, the longer the light, the more effect, but the color, we didn't know. 

And that relates to what photo pigments and photoreceptors in your eye are mediating this effect of light on your body. 

So we systematically had to expose people to very narrow-band colors of light. So if you think of the rainbow, we took very narrow slits of light and exposed everybody to these colors, and you have to also expose them to different intensities. So different wavelengths, different intensities. 

When it all came out, we found that it was light of blue color, about 460 to 480 nanometers, that's the length of the wavelength if you look it up. And that's because the photo pigment in the eyes that was discovered at the same time we were all in this light revolution, so to speak, it responds to the photo pigment of the retinal ganglion cell photo pigment, which we've now called melanopsin. 

You all know about the rods and the cones, that's for vision, but we have deep in the retina another photoreceptor that is directly photosensitive to light right there, nothing to do with the rods and cones. 

And in there contains a photopigment called melanopsin. And the maximum wavelength that stimulates this photoreceptor to have an effect is blue light, 480 nanometers.

Jonathan Wolf: So the blue light is the thing that's going to really reset my body clock.

Prof Debra Skene: It is better than green or red. Don't make the mistake that green and red aren't effective, just when you head-to-head them at the same concentration.

Jonathan Wolf: Got it. So everything will reset my body clock, but the blue light is going to have more impact than the other light.

Prof Debra Skene: So if you want to optimize or maximize affecting your biology, then you design a light that's got more blue in it. 

But contrary, if you want a light, say in the evening in your bedroom, that isn't going to affect your biology, then you should remove the blue from the light.

Jonathan Wolf: I actually think that's a brilliant point to maybe transition to practical advice for listeners. 

So I think you've sort of painted this picture for why this is all so important. I'd love to now discuss what can a listener do to try and have the best possible health benefits? 

The biggest question I had before this episode was, does blue light from our phones really matter for affecting my sleep?

Prof Debra Skene: Yes, but it would depend on how far away. It's all about how much light, how many photons of light get to your eyes. So once you know the principles, you can make it all safer. 

But of course, it depends how close the light is to your eye. The further away it is, the impact is reduced. Then of course, because blue light is the most effective as we've described why, now you could filter out your blue. 

So you are well aware of the Night Shift mode on mobile phones where it gets a bit dimmer, a bit more orangey. You also get the sort of software that you can put on your laptops to cut out the blue. And so these are all a direct result of our original research showing the blue light is the most effective: all these gadgets and blue filtering ideas.

Jonathan Wolf: And so Debra, I've always thought maybe this was a bit of a gimmick and that the amount of blue light from a phone might not really matter. Was I wrong?

Prof Debra Skene: The blue part is the sexy bit, but it's also light intensity. So you do just as well to reduce the light intensity as you would to get rid of the blue.

Jonathan Wolf: Got it. So it's not like, "Hey, get rid of the blue and you're fine, smash orange in your face, you're fine." It's more like the biggest thing is just reducing the overall intensity. 

Prof Debra Skene: Yes. 

Jonathan Wolf: So if I am going to be looking at these devices and I guess a TV would be the same, therefore as a phone...

Prof Debra Skene: The equation for the impact is it's squared. So by every distance you move, you really are reducing the impact by moving it further away from your eyes. 

So reducing intensity is key. I mean, now you can buy blue light filtering glasses that you can wear while you're doing your laptop work in the evening to reduce the blue, and that could also reduce the intensity. 

So it is about getting less light into your eyes at night.

Jonathan Wolf: What would your other key bits of advice be for someone who wants to make sure they're tackling sleep, having just heard you describe how important this regular body clock is?

Prof Debra Skene: We are saying don't have bright blue light at night. Please have dark bedrooms, as dark as possible. 

But the other aspect is the beneficial effects of blue-enriched light, and that would be in the morning. So to synchronize, we've already discussed how important this role of the light-dark cycle is in synchronizing your body clocks, your best way of staying on track with the light-dark cycle is to have blue-enriched light in the morning. 

Now I'm calling it blue-enriched light because we don't go around having blue lights, because that then when you look away from blue light, you get this yellow reverb. It's blue-enriched light. LEDs are blue-enriched. 

If you look at the spectral composition of an LED light or the spectral composition of a fluorescent light, there's a blue peak in those lights. So that works well for using light if you have to in the morning to keep your clocks synchronized to your environment.

Jonathan Wolf: And so presumably, if I lived somewhere really nice like the Mediterranean, I would just go out in the morning and the sun is shining and I would get all of this naturally. Or if I lived in Africa where we all evolved, this would just happen.

Prof Debra Skene: Yeah.

Jonathan Wolf: But for those of us listening to this, in the Northern hemisphere, and the alarm's gone off, and either it's already dark out, still dark outside, or actually it's so gray that doesn't feel very different. What should I do?

Prof Debra Skene: People use artificial lights. The cheaper and more effective option is to go outside. Daylight is a hundred times, 500 times more intense than artificial electric light. If you can go out, the best advice would be once you've woken up naturally without an alarm clock, try and go outside within one or two hours and get...

Jonathan Wolf: And even in the winter, I'm actually getting more light than I get inside. 

Prof Debra Skene: Yes. 

Jonathan Wolf: So you're sort of saying it's actually a lot brighter than I realize, and my eyes see this.

Prof Debra Skene: It's a lot brighter. It's a logarithmic scale. So it's 50,000 lux, 100,000 lux outside, and we are only dealing with 10,000 lux in one of these bright boxes, even in England in November. 

Jonathan Wolf: And is this only going to improve my mood? Or do you believe, I understand you might not have all the data, but do you believe that if I'm doing this regularly, this is supportive for my long-term health?

Prof Debra Skene: Definitely mood, definitely helping with sleep, but also likely affecting metabolism because clocks are deeply involved in metabolic processes. This is one of the more recent functions of clocks.

Jonathan Wolf: I think that's actually a brilliant transition to my next biggest set of questions, which were all around meal timing, which is a topic that we've talked about quite a few times on the podcast. 

There's a lot of nutrition science interest. But you're coming at this from this completely opposite angle about clocks. And I understand you've recently been studying this. So what is the advice you can give us?

Prof Debra Skene: Everybody has focused for so long on what you should eat, but it's now about when, and is there a correct or appropriate timing of food? 

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And there are bigger experts than me at this, but we've done some very controlled lab studies where the question has been, "Okay, let's shift the whole meal schedule by five hours." So that would be breakfast, lunch, and dinner moved five hours, and then what happens to our body clocks? 

And food does not affect our master clock in the brain. So we know that now, we were the first to show this. It had been shown in animals, but we were pleased to see this exactly right. 

So we suspect that food affects probably all the peripheral clocks involved in metabolism, like the liver clock, the pancreas clock, but it doesn't go to this clock in the hypothalamus, so that makes some sense. 

We shifted this meal timing by five hours, and we found that glucose, the rhythm of glucose, also shifted by five hours, so it has the ability to shift the rhythm of glucose. Not any hormones that are driven by, it doesn't shift the melatonin rhythm, for example. 

Whereas light shifts the melatonin rhythm, the food only shifts the glucose rhythm.

Jonathan Wolf: So you're saying that if I regularly eat on a different pattern, my body, my gut, everything will get used to it and sort of digest it easily if I'm doing that all the time. And so it's almost on a separate body clock. 

I'm thinking about Spain where they all eat at midnight but somehow you are on a schedule where that is normal for you. Whereas if I eat at midnight, my blood sugar would go through the roof.

Prof Debra Skene: We believe that our bodies have a memory of the meals we've had before. And so indeed the healthy thing is to stick with what you do normally. 

So Spanish people eating late, that's something they're doing all the time. It's any disruption to that normality that is a disturbance for the clock system.

Jonathan Wolf: So Debra, are you saying that in terms of meal timing and health, consistent timing of meals is important?

Prof Debra Skene: I think it's going to turn out that it's right that we should have consistent meals at the same time and we should reduce this food irregularity. 

I definitely know there are researchers at Kings that study this and others. So it's this food irregularity that we are all beginning to think isn't good for your body.

Jonathan Wolf: I think you're saying that eating at the same times in the same pattern is probably good for your health. But I think you're also saying that if during the week you're waking up early and then having your breakfast at seven, but you're exhausted at the weekend and therefore you're sleeping in till nine, you probably don't want to drag yourself out of bed at seven in order to eat your breakfast.

Prof Debra Skene: Exactly. That's what I'm saying. So when we say to people they should have consistent meal timings that shouldn't change, we should see what those are first.

Jonathan Wolf: I know you've also expressed opinions around Daylight Saving Time. This time when, twice a year, our clocks change by an hour. 

I was thinking about this this morning because I know it always creates havoc with my kids and particularly my daughter's sleep pattern. It takes at least a week for her to get back into the right pattern. 

I understand we did that because we think it's a good idea when we introduced it as governments, probably a hundred years ago now. Is it a good idea?

Prof Debra Skene: We believe being on what we would call standard time, which is the time that we have during the winter months, is the better time for your health because in the standard time, our body clocks are more aligned with where the sun actually is. 

So when we are in the standard time, when we go outside at noon and they're more closer together. When we are in British summertime, there's a bigger gap. So there's more of a mismatch between our body clocks, which is driven by the sun clock, our light-dark cycle, all the things we've talked about today, and this man-made social clock. 

Any mismatch between our social clock, that clock, and our body clocks, the more unhealthy it is. 

So how would you study really the effect of, what is it, six months? It's a six-month period, and how do we know how it would be different if we just stayed on standard time? 

So we can only just use the principles that we don't want to suggest anything that makes the gap between living according to the light-dark cycle and the sun clock and our body clocks. And anything that makes that gap bigger with the social clock has got to be worse for our health. That's where we are now. We just have to prove it.

Jonathan Wolf: Amazing. I would like to do a quick summary, if that's all right, and just correct me if I've got any of this wrong. 

So I start with my most fascinating discovery, which is chronobiologists do not wear watches. And that's because basically living in line with our own internal sense of our body clock is the best way to be. 

You gave this brilliant example about how Daylight Saving Time actually isn't good for you because you want to be just close to where the sun really is. 

I think the other extraordinary thing I heard is that night shift work actually increases your risk of cancer, which, it's not just, "Oh, I don't feel very good," or, "I put on a few pounds." It's cancer, diabetes, cardiovascular disease, and it just tells you how important living in line with our biological clock is. 

Also that everyone should not go to bed at the same time. Some people have a slow clock, which is described as an owl. They want to go to bed late and wake up later. Some people have fast clocks, and so they're morning people, and this is real. It's not made up. 

There's this thing called social jet lag. So the difference between when you wake up when you're working, and when you wake up at the weekend for most of us matters. 

You said if I had a two-hour difference between this, which I definitely do, that probably puts me at risk of putting on more body weight and reducing my mood. So that is not a good way to live. 

That we do understand a lot about how this all works now. So we understand that the light into our eye is then sending this information to this master clock in our brain that communicates it elsewhere. And this is really important.

Interestingly, you said one of the most important things is separating when we eat from when we don't eat. And I think since most of our listeners are very interested in nutrition, it's nice to hear how important that is. 

Then we talked about, okay, we're going into the winter, what do we need to do? And I think my key takeaway is we need to make sure we're getting enough light, and that's at both ends of the day. 

So in the morning you're saying, actually by far the most important thing you can do is to go outside. There's actually much more light out there than you realize. So if you're not going outside, and it's very easy not to do that when we're commuting or we're working from home or whatever it is, that daylight is actually a hundred times more intense than artificial light. 

So even though it's the winter and it feels overcast, actually I'm getting a really good benefit and that's getting me going in the morning. And on the other hand, I really need to think about my experience at the end of the day if I want to keep a good cycle of sleep in the winter.

That blue light is the most effective thing for setting our body clocks or messing up our body clock. And so this idea about putting my phone into a night mode can make sense to reduce it, but actually don't really obsess about the blue light. It's the brightness that's the most important thing. 

So if I have really bright light, but it's got less blue, it's actually worse than the normal thing. So I should be conscious of that. 

Make sure the bedroom is really dark. Set myself up so I'm not watching all these bright things before I go to sleep, but recognize that I need more light, particularly if I'm one of these people whose mood is being affected. And it sounds like everybody's mood has been affected a bit. Some people have this in a very bad way. 

Then finally we talked about when to eat, which again, is gonna be even more important, I guess, as we're going through these winter months. And the critical thing here is all this evidence about consistency. 

So your body is learning these patterns of when you have breakfast and when you have your snacks and when you have dinner, and you want to keep that steady. 

So again, you'd like to have less of this social jet lag between the weekday and the weekend, but if you're normally waking up and having breakfast at seven in order to go off to work and you get to the weekend and you're exhausted, don't wake up just in order to have breakfast at seven. 

You're saying on balance, your gut sense is better to sleep in and let that break, but the more that you don’t then stay up really late and try and keep this in sync, better for our long-term health.

Prof Debra Skene: Yes. Well done. That's a great summary. Please come and be one of my students.