The science of winter depression with Prof. Debra Skene – leading chronobiologist

28:09Debra Skene: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.

28:59Debra Skene:And it's that difference between your weekday working day and your free day, that difference, Till Roneberg has called social jet lag because it's a sort of jet lag. It can be up to one or two hour 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. So let's say it's two hours. Let's say I wake up at 7am during the week and at the weekends I wake up at 9.

29:48I'm at risk of putting on more weight?

29:51Debra Skene:You are. That's definitely published. Wow, that's extraordinary. 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 have slept a little later. And so that gap between the working day and the free day was reduced. That's really interesting. I definitely shifted my sleep because suddenly I didn't need to commute. 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.

30:36I'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?

31:02Debra 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 photoperiod 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 like seasonal breeders or animals because of course you can so clearly see their seasonality. You know as some animals change the color of their coats, they get fatter, they are breeding and we know how the photoperiod, the light-dark cycle, we know how that affects and changes all of these coat growth and reproduction, etc.

32:11Debra Skene: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're all trying to study. Do we have seasonality? Well, we certainly have seasonality in, for example, the incidence of diseases. And 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.

33:04Debra Skene:Do we have seasonality in our hormones and in our metabolites and in our response to pathogens, etc.? So, you know, these are questions that we don't fully know the answer to. As we're going into the winter, what do we know is happening to our body clocks and how might that affect us? 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 that's the blue light that is more effective than red light. But we believe that the biological clocks have a tendency to get later. So we wake up later.

33:55Debra Skene: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 designed 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.

34:37Debra Skene:We've got our studies here in Guilford, 50 degrees north. So that is changing as well. And 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're not exposing ourselves to the darkness of winter as we would have 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.

35:37How 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. I'm 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 and not jed 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

36:04Debra Skene:real there and very real no this is this is really where we have strong evidence seasonal affective disorder so that's in about one to ten percent 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. But the subsyndromal, 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.

37:19Debra Skene:There's 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. And the impact you would expect to see is just to affect your mood or does it affect other things? You mentioned before about impact on maybe like your cravings and weight gain and things like this. 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.

38:03Debra Skene:So likely direct effect on mood areas in the brain to improve mood. And Debra, I know you've studied a lot the effects of particular colors of light, and I understand blue light in particular. Why not does the color of light matter? 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 photopigments 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.

38:53Debra Skene:So if you think of the rainbow, we took little 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. And 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 photopigment in the eyes that was discovered at the same time we were all in this light revolution, so to speak, it responds to the photopigment of the retinal ganglion cell photopigment, which we've now called melanopsin.

39:43Debra Skene: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. So the blue light is the thing that's going to really reset my body clock. 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.

40:33Got it. So everything will reset my body clock, but the blue light is going to have more impact than the other lights.

40:39Debra 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. I actually think that's a brilliant point to maybe transition to practical advice for listeners. I think you've sort of painted this picture for why this is also important. I'd love to now discuss, okay, 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?

41:27Debra Skene:Yes, but it would depend on how far away. You know, 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're 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.

42:19Debra Skene:And so these are all a direct result of our original research showing the blue light is the most effective. All these like gadgets and blue filtering ideas. And so, Deborah, 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? The blue part, you know, 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. 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.

42:59Yes. So if I am going to be looking at these devices, and I guess a TV would be the same, therefore, as a phone.

43:05Debra Skene:Just have your television. So the equation for the impact is it's squared. So really, 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 they could also reduce the intensity. So it is about getting less light into your eyes at night. If you know someone whose mental or physical health is affected during the winter months, why not share this episode with them right now?

43:48I'm sure they'll learn something that will help them weather the storm. 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?

44:04Debra Skene:We're saying don't have bright blue light at night. Please don't. 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, 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 light because that then, when you look away from blue light, you get this yellow reverb, you know.

44:59Debra Skene:It's blue enriched light. And 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. Presumably if I live 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. But for those of us listening to this, you know, in the Northern Hemisphere and the alarm's gone off and either it's already dark outside, still dark outside, or actually it's so gray that doesn't feel very different.

45:56What should I do?

45:57Debra Skene:Well, people use artificial lights that you can buy. But I do want to come back to the cheaper and more effective option is to go outside. Daylight is 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 and even in the winter i'm actually getting more light than inside so you're sort of saying it's actually a lot brighter than i realize in my eyes it's a lot brighter it's a logarithmic scale so it's 50 000 lux 100 000 lux outside And we're only dealing with 10 ,000 lux in one of these.

46:50Debra Skene:Even in England in November? Oh, yeah, yeah, yeah. 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? 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. I think there's such 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 because there's a lot of nutrition science interest.

47:35But 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?

47:44Debra 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? 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.

48:34Debra Skene: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, but not any hormones that are driven by it. It doesn't shift the melatonin rhythm, for example. Whereas light shifts the melatonin rhythm, the food only shifts the glucose rhythm. 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.

49:25And so it's almost on a separate body clock. Think about Spain where they all eat at midnight or something. Somehow you're on a schedule where that is normal for you. Whereas if I eat at midnight, my blood sugar would go through the roof.

49:38Debra 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. So, Deborah, are you saying that in terms of meal timing and health, consistent timing of meals is important? 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 the food irregularity. I mean, I definitely know there are researchers at King's that study this and others.

50:25Debra Skene:So it's this food irregularity that we are all beginning to think isn't good for your body. I think you're saying that eating sort of 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 into nine, you probably don't want to drag yourself out of bed at seven in order to eat your breakfast. 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, you know, first.

51:08I know you've also expressed opinions around daylight saving time This time when like twice a year our clocks change by an hour And I was thinking about this this morning Because I know it always creates havoc with my kids And particularly my daughter's sort of sleep pattern It like takes at least a week for her to like get back into the right pattern And I understand we did that because we think it's a good idea When we introduce it as governments, you know, probably a hundred years ago now Is it a good idea?

51:38Debra 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're in the standard time When we go outside at noon And they're more closer together When we're in pretty summertime There's a bigger gap So there's more of a mismatch Between our body clocks Which is driven by the sun clock You know, our light-dark cycle All the things we've talked about today And this man-made social clock and any mismatch between our social clock, that clock, and our body clocks, the more unhealthy it is.

52:38Debra Skene: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, you know, we don't want to suggest anything that makes the gap. between living according to the light dot cycle and the sun clock and our body clocks and anything that makes that gap bigger with the social clock is got to be worse for our health. That's where we are. Now we just have to prove it. Amazing. I would like to do a quick summary, if that's right, and just correct me if I've got any of this wrong.

53:24So 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. And you gave this brilliant example about how daylight savings 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 is not just, oh, I don't feel very good or I put on a few pounds of weight. like cancer, diabetes, cardiovascular disease.

54:03And 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, sort of when you're working and when you wake up at the weekend for most of us matters. And if 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.

54:42So that is not a good way to live. We 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. And interestingly, you said one of the most important things is sort of separating when we eat from when we don't eat. And I think since most of our listeners are very interested in nutrition, you know, it's nice to hear how important that is. And then we talked about, OK, 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 given enough light.

55:18And 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 and so even though it's the winter and it feels overcast actually i'm getting a really good benefit that's getting me going in 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, the blue light is the most effective thing for setting our body clocks or messing up our body clock.

56:00And so this idea about putting my phone into like 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 really bright light, but it's got less blue is actually worse than the normal thing. and less. 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 has been affected. And it sounds like saying everybody's mood has been affected a bit.

56:36Some people have this in a very bad way. And then finally, we talked about when to eat, which again is going to 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. And so again, you'd like to have less of this sort of 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.

57:13You'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.

57:25Debra Skene:Yes. Well done. That's a great summary. Please come and be one of my students. As you can imagine, hosting this podcast, running Zoe, juggling family life, it all keeps me pretty busy. So I try as best I can to stay energized and show up well in all those parts of my life by fueling my body with the right food, by exercising, and by adding a scoop of Daily 30 to my meals every day. If you haven't heard of Daily 30 yet, it's the gut supplement designed by our gut health scientists here at Zoe. It's made of over 30 high quality hand-picked plants, including seaweed, fungi, and different types of fiber.

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58:43so order yours today at zoe.com daily 30 thanks for listening and see you next time