Daytime Light Exposure and Health

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Eligible students get a year of Microsoft three hundred and sixty five premium and a year of Xbox GamePass Ultimate with a custom color Xbox wireless controller. Learn more at Windows dot com slash student offer. Law supplies last ends june thirtieth turns at aka dot mslash college pc. Many of us are no strangers to late night phone scrolling, only to find ourselves afterward unable to sleep staring at the ceiling like owls. Indeed, research from around the world has shown that the quality and quantity of sleep has diminished. For years, the prevailing explanation for this insomnia has been that blue light emitted from our devices tricks our brains into thinking it's daytime, disrupting circadian rhythms and prompting we hour restlessness. Blue light at night is bad because it makes your brain think that it's not nighttime anymore, that it must be morning. But now some scientists are challenging the idea that the glow of our phones is the reason we're sleepless and unsettled. We went and tested it and we couldn't find strong evidence for a bright screen affecting the time taken to fall asleep compared to a dim screen. Welcome to Big Picture Science. I'm Molly Bentley. In our regular look at critical thinking, we turn a spotlight on blue light. Is it causing sleep difficulties? Here why some scientists now doubt the link, but don't let our phones totally off the hook . And they zero in on other explanations . It's skeptic Blue Light Special . The blue light is special. When the blue colored light emitting diode or LED was invented in the nineteen nineties , it provided the crucial missing component to produce bright, energy efficient white light. The breakthrough revolutionized electronics. We swapped our incandescent bulbs for efficient LEDs, and the screen displays on our phones, TV's, and monitors became more vibrant. So transformative was the blue LED discovery that its inventors received the Nobel Prize in physics in twenty fourteen. The sun, though, is our biggest source of blue light. It produces it naturally. The short energetic blue w aves are one part of the rainbow of colors emitted from our star that combine to produce white light. And it's the blue light in sunlight that prompts your body's wakefulness. But as we know we're, exposed to more blue light than ever. The LED bulbs illuminating our ubiquitous devices bathe us in artificial blue light . And for years, studies have attributed the growing epidemic of insomnia , particularly among teenagers, due to the blue light from our glowing screens , but recent studies challenge the conclusion that blue light means a bad night of sleep. Back in twenty eleven, we did a review paper looking at the relationship between technology use and sleep. And we were even under the belief that technology caused sleep issues, and we proposed all these different mechanisms . And then over the period of a decade or more, we were doing research to test this other people were, and suddenly it was like, hang on, something's wrong here. I'm doctor Michael Gratesser. I'm a sleep researcher and a clinical psychologist who specializes in the treatment of sleep disorders . Michael, what I found most interesting about your conclusion that blue light from our phones may not be the sleep stealer we once thought is that you drew this conclusion years before the idea that blue light affects sleep took hold in the popular consciousness . Yeah , that could be said. I mean, it really sort of started when we were doing a review of what aspects of technology could affect sleep . And we kept seeing in the research literature. And we're sort of talking like twenty eleven, twenty twelve , that a lot of people were mentioning that the blue light from screens could affect sleep, but we're also noticing that no one was testing it. And so we had the luxury of being able to do that . You know, we had a sleep lab and so we thought, well, let's go and test it. And so technically speaking , when it came to this whole concept that potentially the blue light from screens could make it difficult to fall asleep , the study that we published in twenty fourteen was the first one in the world to demonstrate that that isn't the case . Okay , so what it sounds like is that people felt strongly that the artificial blue light was keeping us up. Are you saying that this idea has stayed in circulation for almost a decade while you have tried to chase it down. Do you call it conventional wisdom? Is it a rumor? Where did the idea come from? Yeah, I think it's been a series of events. I mean , you know, if you go back, say, for example, early two thousands , it has been demonstrated that compared to other colors, blue light can suppress melatonin and it can make us more alert . Then what happened is probably Circa twenty twelve or thereabouts . You had Apple releasing their iPad too and they actually had this kid that was looking at this iPad with this glow of light that had this blue tinge to it. And there was this massive uproar amongst the sleep community. So that's when we started to think, well, let's actually test it. No one's tested it. We went and tested it, and we couldn't find strong evid ence for a bright screen affecting the time taken to fall asleep compared to a dim screen. We published those results in twenty fourteen and I think the next major event happened the next year. There were actually studies that came out that were still testing this idea. One came from Switzerland . It similarly didn't really show that there was much effect on the time taken fall asleep, but it was the study that came from Harvard that got massive attention . And in their summary of their study they say that the time taken to fall asleep was significantly longer. When you dig into the actual study, it took about nine point nine minutes. Now, that's a bit questionable, you know, is that really a meaningful difference? But it sounds like when the researcher said it takes significantly longer, that was the phrase that stayed with the public . Exactly. And what that means is it was from a statistical point of view longer, but the next step that you have to take is really what does that mean? Is it a big enough effect ? We found a difference. I think from memory, it was an average of three point three minutes longer if people used a bright screen that had this peak of blue light coming from it compared to a dim screen. And I think a lot of people understand units of measurement in terms of time and they understand how long things take. So is nine point nine minutes really that meaningful? We found it was three point three minutes longer . And so what really happened is that in parallel , you had the research field that was still testing this idea. Yet what was happening on the internet and through the media was this sort of rise in this belief that blue light from a screen will dampen your melatonin and make it harder to fall asleep. It's really fascinating that I mean I just have to say personally because I thought your research was very new, that this was established science and that you were in some ways an outlier, but it was the other way around . Because Michael, you know, it feels right. Maybe that's why the idea had this currency because it feels like staring into your phone for hours does turn you into an insomnia owl . So the causation felt right at a gut level. Exactly. And I think this is, you know, besides the frustration, I was feeling that because people kept saying this and it started to amplify more people saying it yet the science wasn't really backing that up. I think my frustration also turned to a typical sort of curiosity. Like what is happening here with the human condition where we go and provide this objective evidence? We do the thing this is a great aspect of science when you're doing you're getting multiple people, independent groups doing research, asking this question and finding the same thing. This whole concept of replication, which is it's helping us understand the way the world works, but then you're getting people who you're explaining this to who are so resistant and wouldn't want to adopt this new information. They just reject it. And it really does show the power of people's own personal experi ence. If a scientific study or a scientific finding doesn't match their own experience, they're more likely to reject that scientific information. I think that's part of the conclusion I'm currently at . There's a whole bunch of people that sort of go, yeah, I've had one experience, maybe a few experiences that I can remember when I was using technology and it affected my sleep . But those experiences, they also stand out. You're not going to remember the things where you use technology and you slept fine . And I think that it's interesting that you sort of say that this was thought as new research when it's been going on for a decade because I think it's very hard to break through the noise of the internet. And one aspect I think that we are learning about science is the translation of science to the community. So what we did is that we got as many studies as we could find. It ended up being eleven studies by the time that we published this review in twenty twenty four , so that we can actually show people that if you look at the results from every single one of these studies , you're not getting this massive difference in the time taken to fall asleep. In fact, if you eyeball it and you average it, you're only talking about a few minutes longer to fall asleep after using a bright screen compared to a dim screen or reading a printed book or having blue light blocking glasses on. Michael, let's bring it back to your research and to some of the specifics. So and I really appreciate you laying out for us what it's been like to wade through the dense force of the internet with your message trying to get to the other side . One thing that was interesting, very interesting is that when we're staring at our glowing screens, they sure seem bright , especially at night . But what you found was that the screen light intensity was too low to actually suppress melatonin or to disturb our sleep. This gets us into a discussion of Lux . Can you take us there what luxe means and what you learned the Lux of our screens? Yeah, sure. So it needs context because fourteen years before we published that study, I was doing clinical work , helping people with their sleep, primarily their circadian rhythms. Circadian rhythms are our twenty four hour body clock. Some people can be in their own time zone physically, but their body clock can drift. And so therefore they're sleeping at the wrong times. Now for context , you need a minimum of five hundred lux intensity to be able to change the timing of their circadian rhythm. Ideally we have like a thousand lux. Can I jump in there with just comparison? I believe a bright sunny day is one hundred thousand lux . At an office desk lamp is five hundred lux . Do I have this right? Yeah, that is definitely the ballpark. And you know, if people want to experiment, they can actually like download a Lux meter on their phone, like an app and just play around with it and point the camera different directions so they can get a relative sense of how bright it is outside compared to inside. And if they focus that meter on our screens , what's the Luxe level? And we should say once again that Lux is the standard unit of measurement for light level intensity. So what is the intensity of our screens? I actually haven't done it with one of these apps, but I can say that when we were doing this study in twenty fourteen, sorry, that got published in twenty fourteen . When I measured the Luxe, it was below fifty Lux . And so I was sitting in the dark, I had an iPad two that had a white background I had on full brightness and I basically had it sitting on my lap as I was sitting on this bed and I had the Luxemeter right near my eyes to be pointing at this screen and I realized that's not bright enough. We're not going to do anything with that. So then I actually raised my knees up. So I had the iPad resting on my knees closer to my face, then I measured it and we had about a minimum of fifty lux , depending upon what was on the screen. And I will tell you now that it was so uncomfortable perceptually to have that bright screen. Like it was like, I don't really want to look at this, especially for an hour . Yet the luxe coming from it was fifty . So I think people can certainly have this perception that it is bright , but that doesn't match physiologically what is happening. And as a result, we don't see the outcome of people taking longer to fall asleep. So you're saying that the intensity of the blue light matters. Now blue light is in the visible wavelength of course and it is the shortest, most energetic they are the most shortest , most energetic waves of visible light . Just stepping aside to have a short discussion here about the physics. How do you compare what is the role of these energetic waves intensity of light in producing a biological effect. Because there's still intense waves, but you're saying that the overall light intensity is not enough to have a biological effect . So two concepts is intensity, which we're talking about lux, just to keep things simple. And the other concept is wavelength. So wavelength is really the color of light. So when we're talking about the colours of light, we're talking about almost like the rainbow . Like when it rains and you've got sun going through basically a water drop, it then breaks apart and you get the rainbow very similar to that pink floyd white beam that's going into a pris m and then it's having those rainbow colors. And it's really the cooler colours, the blues and the greens that are energetic that have this ability at lower intensity levels, lower lux leevels to be able to suppress melatonin and shift the timing of the circadian rhythm . But one thing that's not the end of the story . If you have red light which is completely on the other side and has often been thought of as a placebo . If you have that at a higher intensity , we actually find that that has an effect . So we did a study where we compared green light versus red light in helping people change the timing of their circadian rhythms, like what I spoke about before, but just in the opposite direction, these were teenagers. So teenagers need the light in the morning . So we had basically our active treatment, which was green bright light . And we had our placebo which was red bright light and both of them worked . So that's when we were sort of like, oh, okay, it's not just the color of light, it's really the intensity of the light . So at lower intensities you'll see this effect with blue light and not so much the other colours, but as soon as you raise the intensity up , then you're starting to see that there's really not that much difference. Let's be clear about why correcting this conventional wisdom about blue light is important. And you've been talking about that , but I thought I'd give you a chance to say it clearly with all the ways that phones can disrupt life, why is this misunderstanding about the role of blue light important to correct? In other words, what's at stake, Michael? What's at stake is that if that's not the cause of the issue , then we are not addressing the issue . And I say that with a full belief because when people come to us with sleep issues, they come from a whole range of different career, occupational and educational backgrounds , but we guide them and anyone can improve their sleep is what I'm under the belief of if they're shown the right direction. And I think we are not showing them from a public health point of view , from From a journalic point of view and a social media point of view, we are not educating them and pointing them in the right direction. And I think that that means that we're going to continue to have problems. Well Mich,ael Gr adar,iz thank you so much for joining us. And thank you so much for listening because it's, you know, being a pain in the arsenal getting people to listen . Michael Gradizar is a clinical psychologist and sleep researcher who has spent decades studying sleep disorders. Well, Roland, we turn to you now. What did you make of Michael Gradizar's conclusions about the role of blue light and sleep? I have to say, I was quite surprised. Well, it's interesting. You know, I made a series for the BBC about circadian rhythms about twenty years ago when a lot of this stuff was quite new and I'd heard about the role of blue light and so when people started talking about it, it seemed to make sense to me and he talked about this Harvard study of twenty fifteen. I saw that and yeah everything fitted into play. So I think one of the things which comes out of this is how enormously sensitive and adaptable the human eye is so that if you think about it it's easy for you to go outside on a bright sunny day and your eyes adapt to it and you go inside and you can see everything quite clearly. But if you do that with a camera , it gets overexposed in the bright light outside. You can bring it inside and suddenly all the details are grainy, blurry, so on . You know, we don't appreciate adaptable our eyes are. It just feels natural. And in fact, so coming up , I've been talking to one of the pioneers in all of this, J Dunlap,, who, you know was one of the people who worked out not only how a body clock works but how it keeps in sync with the rising sun and the setting sun . Defining characteristics of circadian rhythms that they can be reset by changes in the environment . Light and temperature are the most common terms . Next, we get in step with our circadian rhythms and the biological mechanism by which blue light waves tickle your brain into wakeful . This is our regular look at critical thinking on big picture science, skeptic check blue light special Hey gang, it's Seth. Check out a new podcast called The Persistence Lab, a show from AbV that tells the stories of the patients, scientists and clinicians who are committed to driving real change in medicine and healthcare and the resilience that pushes them forward. These aren't headlines, they're deeply human moments that show how progress happens one step at a time . You can find the persistence lab now on your favorite podcast platform. Inside each of us is a clock that regulates our sleep and our wakefulness. I'm J Dunlap. I'm a geneticist and molecular geneticist at the Geyso School of Medicine at Dartmouth, and I work on the molecular basis of circadian rhythms using genetics and molecular biology. To better understand the role that artificial blue light might play in keeping us awake , we need to explore the fascinating science of natural blue light. After a ninety three million mile journey from the sun to our eyes, blue light waves signal to our brains that it's time to start our day . They set our circadian rhythms . But before the molecular genetics revolution of the late nineteen eighties , the idea that our bodies were regulated by internal clocks was a kin to pseudoscience . Even when I was beginning, it was not respectable. I got grant reviews that likened rhythms to studying spoon bending because it sort of defied logic. Now a lead researcher in a respectable field, Dr. Dunlap told Roland Pease , that light sets our internal clocks, which generate our circadian rhythms. That's circa for around and DN for day , which in turn regulate almost all of our biological functions . These are rhythms that have a period length of about a day, but not exactly a day under constant conditions and they're characterized by persistence that is they 're robust and they continue to run under constant conditions . They can be reset by abrupt changes in the constant environment. So abrupt changes in light or temperature or other things. These are cycles as it were in things like metabolism, I guess. Yep. You name it, metabolism , behavior, almost any physiological parameter you can think of controlled in a bigger little way by circadian rhythms. And it's not just us, I think, amongst the organisms you're interested in is bread mould . Yeah, well fungi are interesting and they're sort of having a renaissance. Now fungi are the group of organisms that share the most recent common ancestor among the panoplay of life . So if you go back, fungi are more similar to animal cells than our plants or bacteria or green algae or whatever. And things that fungal cells do, they tend to do in the same way that animal cells do. And so they eat carbon, eat glucose the same way, they make proteins the same way . They shuffle proteins around the cell in the same way. Their cell division cycle is very much the same. And the molecular basis of their circadian clock is very much the same . What's a daily cycle look like with a fungus? You mean what does it control? Yeah, what do you see? The most obvious thing is the way they grow. When they're when they're growing in the daytime or late in the day they will send hyphae up into the air and make spores and when they're growing along at night they will just run along the surface of whatever they're growing on a piece of bread or auger plate or whate ver . But like with any organism, different fungi will use the clock to control different things. So the model system that we study is one of the classic genetic model systems calleds. ne Itur' ospora the bread bowl . It controls this growth habit. So the most obvious thing is this growth habit, but when you start digging in, just about everything is controlled in some way. I mean that sort of slightly surprises me that they would do that. For us humans, the point is in effect that , for example, we're ready to wake up when the sunrises. That's right. People are ready to wake up when the sunris es, but clocks are adaptive, so they're not required. You can eliminate the clock and a cell or an organism will still be alive , but they don't deal as well with the environment. So clocks are used to anticipate these regular changes. So in that context, the fungus needs a clock just as much as people do because it's a big deal when the sun goes down , right? It gets cold , there's no more DNA damage from ultraviolet rays . Availability of food could change . And you know, for people, obviously there's a gazillion things that are different when it's dark outside. So we got this sort of internal mechan ism essentially to keep ourselves sort of maybe even slightly ahead of the game, but in sync with the environment in which we're living and that changes throughout the day and night and therefore it's to anticipate changes that the organism knows or can know will happen so that you're ready. A background I'm a physicist and so this is a question which has always interested me. If you have a clock, then you have a mechanism that's driving the clock. And so for example, with a classical clock , that's a pendulum that's swinging backwards and forth and that regulates the way that the clock progresses. What's the pendulum inside me ? it's an oscillator as a pendulum is , but it's a self sustained oscillator. So not like a relaxation occillator. And it's a negative feedback loop . And in fungi and animals, it's a single step negative feedback loop. You have two proteins that work together , a heterodimer and that acts as a transcription factor. So transcription factors are proteins or complexes of proteins that derive gene expression. So this transcription factor, this heterodimer, sits on the DNA of clock genes and it drives their expression . So you'll say this so it's not a mechanical clock as a pendulum would be, but it's a sort of genetic molecular clock. That's right. That's exactly right. That's sort of you get more of these proteins during the day or less than what is driving the rate at which the proteins are made and so on. That's right. You get more of the proteins at some time and then the proteins physically form a complex and that complex feeds back and interacts with the heterodimer and turns it off. So you can sort of imagine this heterodymer makes RNAs, makes proteins, proteins feed back , touch the heterody and make it not active so you make less protein. And that's sort of going up and down during the day. Over twenty four hours. Is that the idea of it? That's right. You have this genetic pulsing as it were. I mean, it's incredibly slow. I always think of chemistry going on in my body being incredibly fast, but this presumably is taking twenty four hours to do that sort of swing back and forth. That's right. Is it is there one place? Is there a bit in my brain or something which is doing this or does every cell have something like this? Almost every cell with a very few exceptions. People used to think it was and this is an interesting case of history or science, I think. People used to think it was all in the in this part of the hypothalamus called the SCN, the supra chasmatic nuclei. So some kind of master clock as it were. Yeah, that was right. People thought that was a master clock and they thought it was a master clock because the output they were looking at was behavior. And through many years of hard work, they figured out that if you if you made a lesion in this superchmatic nucleus, you lost the behavioral clock . So ergo, it must be that the clock was in the SCN . But then when a guy named Julie Schivler in working in Switzerland fell upon the fact that looking in cells and culture, these are mammalian cells and culture that they had a clock too. So even disembodied cells do this. Listen, these are cells that have been in culture for twenty five years . And if you could synchronize them, then they had a clock also. So then people started looking in organisms in sects , in multicellular organisms , and sure enough , almost all the cells have clocks and they all run in the same way. It sounds like they're all talking together. It's collective action in a way. That's right. They are all talking together and they're talking together . So obviously neurons can talk to each other through electrical signals, but non neurons can talk to each other by touching each other and by sending out chemicals that have receptors that can talk to each other . We have a rhythm in body temperature and that impacts all the cells . So all cells are kept pretty much in synchrony. Now the other part of this, which I think is where we come close to what the subject of this edition of Big Picture Science is about is that if I have a pendulum clock , I tend to have to go back there every few days because it's drifted out of sync with real time and have to correct it . And as I understand it, our own body clocks need the same thing that they will just drift off real time given the chance . That's correct. And so this is the I 'm probably the second characteristic or third idea for defining characteristics of circadian rhythms that they can be reset by changes in the environment. Light and temperature are the most common terms in the jargon these are called zeitgabers from the gabers. I like that for time givers. So fungi and mammals are reset in the same way. You have this negative feedback loop, and light acts to increase the expression of these negative elements. So the heterody m serits on DNA, makes proteins and those are negative elements. So nudging it from out nudging the cycle from outside in a funny way. That's very that's right. Nudging the cycle from outside. So you can sort of imagine this , you can see my fing er here drawing the curve if the negative element and it's there cycling in a mount . So if you're on your way up to the peak and the organism sees light, you immediately increase expression. So that's like immediately jumping to the peak. So if it's on its way up and you see light, then you get a phase advance. It sort of pushes it forwards. Pushes it forwards. If it's on its way down, the organism sees light , it goes to peak and that's like setting it back in time back to the peak. So you get a phase delay. So it's as you say, it's nudging it. And that's what keeps it, that's what means that in a sense every day when I wake up and I see the sun in the sky that's right it sets it to a point and it keeps it going and then it just runs from there and the next day it does it again I guess the one other aspect then to tie this all together is these circadian rhythms are pretty important in terms of our health because there are times when we need to be doing things and when we're not doing things , the body does sort of maintenance and so on. Give me a sense of why we have evolved these sort of daily cycles in the first place . So we evolved them in order to anticipate regular ch anges , but they've come to be very important for how we normally operate. A great case in point, I think, are experiments done in Joe Takahashi's lab , they took a mouse and knocked out the clock in the pancreas . So it's a typical mouse . It runs at night, it doesn't run during the day. And the only thing that's wrong with the mouse is it doesn't have a clock in its pancreas . Okay . And if you give it glucose, it still makes insulin. All that's normal. But within about ten or twelve weeks, the mouse becomes di abetic. Okay, and that's because presumably because loss of circadian regulation because that's the only thing that's been changed. You've lost the clock. So it can still respond to insulin respond to glucose, but the regulation has been screwed up. And there are other cases like this that clocks are used to integrate in a large sense all of our physiology so that your liver is talking to your kidneys and your muscle cells are talking to whoever they need to talk to and your brain is sending out signals and the receptors for the signals are there when they need to be there. And this whole thing is working together quite well. But why does being out of sync feel so awful? It's a great question, and I'm not the best person to answer it . Things that are happening at the wrong time of day . And when you disrupt this sort of mutual regulation , then you tend to feel badly. And a good example this is jet lag . So it takes a couple of days to reset these things for everybody to get back into sync. So that's when you're jet legged . When some of your clocking at one time a day and the receptors for other things are tuned to that and the other part of your clock, other your brain is saying it notes, it's the other time of day . So we all experience, or most of us have experienced this circadian dysfunction. And what about the quality of the light? For one thing, is this just working through my normal vision? That's correct. So is in my eyes? Is it that the signal's coming in? It is. In mammals, in people, all virtually all of our photoreceptions through the eyes. And this is also an interesting story, I think. You see light and the light makes a neuronal signal and it goes back through the optic tract to the optic chiasm, which is in the back of the brain. And then immediately on top of the opticiaism are these suprachismatic nuclei that I talked about earlier . So when you think about photoreception, it's an interesting case. So when I look at you on the screen here and I pick my eyes up and look at my spouse across the room , I don't see you, I see her. So I need a rapid refresh for image formation . But for circadian timing, you don't need a rapid refresh. You just want to collect all the light you can get . And so actually there are different cells in a different place in the eye that are involved in circadian photoreception and actually a different pigment that's involved in circadian photoreception. Right. So it's part it's in the eye, but it's not part of our vision, you're saying. It's not part of our image formation vision. It's part of our circadian vision There are several layers of photoreceptors in the eye. There's rods and cones and then actually it's on top of the rods and cones are other cells that collect information for each one of those . And eventually these get to things called retinal ganglion cells , which assimilate information from rods and cones and other cells. And the circadian photoreception happens in these retinal ganglion cells through a different photoreceptor that collects light and integrates the amount of light over a longer period of time. And that's what sends the signal back through the optic chiasm to the clock in the brain. You're saying that it's a different photos receptor? Is that where this whole idea that blue light is important in this story comes from? Blue light's also important for vision for image for mation. But yes, it's a retinol based photoreceptor, so it's sensitive to blue and green light, you know, and not so sensitive, much less sensitive to red light. Are you saying that if you were to shine red light at me in the morning rather than me seeing the sunlight, that wouldn't help entrain is the word I think. Wouldn't help as well. Wouldn't help as much. Yeah, that's right. And that's, of course, that's why blue light is at night bad because it makes your brain think that it's not nighttime anymore, that it must be morning or it's a long day. So you think it's plausible then that seeing blue light at the wrong time of day can be disruptive to our sleep patterns or at least to our, I guess, physiological cycles. Yes . Yeah, I think that's been demonstrated and I'm not the best person to talk about that, but I think that's established fact that seeing blue light at the wrong time of day will disrupt your sleep. Jake Don Luck, thanks very much for talking about this to big picture science. Yep, this is fun. Jay Dunlap is a geneticist and molecular geneticist at the Guisel School of Medicine at Dartmouth. Molly, I think you'll get now why it is that I bought into this idea that blue light could actually change our sleep patterns if we were using our devices wrong. You know, the physiology is there, the biology is there . And I never even thought to question it when people started saying change your habits with your devices because I was all set up for it. Kind of amazing that this research that Jay was describing just a few decades ago was not deemed credible. Well, you gotta think that I come back to this idea that it's so instinctual that you wake up in the morning and we don't particularly worry about it that actually what's happening is this body clock is getting your blood pressure raised a bit in the morning. It's getting your heartbeat ready. So basically it's like when the pilot is doing the systems check on the plane before you take off. You got to do that and then the plane's ready to go. And if you wake up suddenly without that preparation you feel groggy. So to work out that this is going on and this is this sort of chemical molecular pendulum that swings back and forth over twenty four hours and there's so much chemistry going on in any case in your body, I can understand why people were thinking this is all bit woo shoo, woo shoo stuff . It's hard to do. Is that the British term for it? I'm sure I borrowed it from an American Coming up, an expert who has studied the effects of blue light on people's health. I think there's a lot in the literature discussing the impact of light at night on health and well being. And there's no question that there is an effect . But I think the biggest effect and something that we are not talking too much about is the fact that we are being exposed to too little light during the day . It's skeptic check, blue light special on big picture science . Eczema is unpredictable, but you can flare less with ebgliss , a once monthly treatment for moderate to severe eczema . 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Before starting Ebglus, tell your doctor if you have a parasitic infection. Ask your doctor about Eblis and visit veglas. Lily dot com or call one eight hundred lilyr x or one hundred five nine seven nine As we heard, the complicated biology of our body's clock is guided by exposure to light. Natural blue light from the sun prompts wakefulness, but we also heard research that suggests that the intensity of the blue light emitted from our phones isn't strong enough to keep us up in the wee hours. The reality is that the interplay of light and sleep cycles is comple . Hi, I'm Marianna Figuero. I'm a professor and director at the Lighting Health Research Center at the Icon School of Medicine in New York. Dr. Figuero has studied the effects of light on our health. In a conversation with Roland, she sheds light on this interplay , including a surprising finding about sunlight. I'd like Mariata to take you back to some of the earli reersearch you did which rather than talk about too much light at night affecting Arsocadia rhythms, you've also done work on too little light during the day. And in fact that sounds like quite a big deal. That is absolutely right. You know, I think there's a lot in the literature discussing the impact of light at night on health and well being. And there's no question that there is an effect . But I think the biggest effect and something that we are not talking too much about is the fact that we are being exposed to too little light during the day. When you think about the built environment and that's particularly true in the United States, for example, where they have those deep core buildings or if anybody has ever visited nursing homes for example, in the United States, these tend to be extreme low light levels during the daytime hours. And what's important is that your visual system is much more sensitive to light than your circadian system for example. So all of us are able to navigate in the space during the day. We're able to do our visual tasks. We're able to see what we need to see , but that doesn't necessarily mean it's impacting our biological clock because we are designed to be outdoors during the day and if you think about how much more light you have outside compared to what you have indoors , it's a huge difference. So it's really interesting to me because I think of the classic office space for example, being all those glaring strip lights , which I think have having lots of blue lights in them and quite cold as it were kind of like compared to natural daylight, but it sounds like that's still not enough to sort of excite this daily regulation. Yeah, it's interesting because being glary doesn't necessarily mean it's being effect ive, right? It could be glary simply because you are able to see a direct view of the light bulb. That alone is glory , right ? And yes, it is true that off ices tend to be higher light levels than, for example, the homes . There's no question about it , but it is still border of activating your biological clock. So to give you an idea of numbers, you're probably exposed to about two hundred lucks at the eye in offices without any windows, just indoor offices. Luxury showed it a b'rightsness. It's the brightness. That's right. That's right. It's how much light is actually reaching the ice surface or the, you know, the cornea . And outdoors in a bright sunny day , you are being exposed to fifty to one hundred thousand . So it's a drastic difference. Like you're talking ten , a hundred times less light indoors than you have outdoors. So my question then is if we go back to this idea that some people office workers and so on aren't getting enough light during the day, have you actually seen that having an impact on the sort of signals or on people's sleep patterns? That's the important part. You know, there is some studies that show that getting more light during the day increases the amplitude of your melatonin levels at night. So it's a signal for that flip flop switch to switch . So the hypothesis is if you have lower of melatonin during the nighttime, you have less of a signal it's nighttime. So it gets confusing, for example . We underest imate the importance of that light during the day and how important it is to improve sleep at night. So some of the work that we have done have shown that by increasing that amount of light during the day helps people sleep better at night . I mean, you have brought us to the nub of the program, which is this question of whether sitting there with your iPad or your tablet or your phone and you're scrolling or whatever and you're getting the blue light from the screen . Is that actually disturbing our sleek patterns or, is that really an overstated effect? Well, it could be both , because I think the most important thing that people don't talk much about it is the amount and the duration of that exposure. So people just focused on the blue light, which makes sense because we know that we're more sensitive to short wave length or blue light . But if you are below threshold in terms of the amount of light, it doesn't matter if it's blue. Zero times zero equals zero, right? So it won't have an effect . So higher light levels are worse because are more likely to have that effect. And the second thing is if you do it for five or ten minutes, it may not have enough duration to have an effect. But if you do it for two or three hours it may have an effect . That's one thing. And the second thing that I always say it's very important even if it's lower light levels and it's not having a physiolog ical effect on your biological clock , it could be alerting you by if you're watching an exciting movie or if you're reading things that are getting you upset , that in itself can alert your system and it can make it harder for you to fall asleep . It's a stimulus, it's the intellectual stimulus or whatever correct yeah. I mean, because the nub of this is that there are people who will sell you special glasses, orange tinted glasses which come out of the blue light or can get apps. I certainly use them because actually I find it more comfortable to reden the screen at night. You know, there's there's money being made here and it sounds to me like that's probably not a necessary route for people to take. Probably . You need to be able to measure these glasses and see what exactly they're removing and filtering out . Some of these blue blockers, I don't know what they're blocking and I don't know how effective they are at blocking anything . So I agree with you that there's a lot of marketing, but there's also a lot of study that needs to be done with different products to be able to say that it's effective or not. Taking the risk of giving people health advice, which I'm certainly not qualified to do, from what you've told me so far , it would probably be far more useful to get away from your screen and go out for an hour at midday and enjoy the outdoor environment for that time than to avoid , you know, or take special measures with your screen time late at night. It may be good in other ways as well. Yes, absolutely. And if I can recommend, I would say go out in the morning earlier and the reason why earlier might be better, it's because it helps advance your clock because we humans have a biological clock that is slightly longer than twenty four hours. So for what we call entrainment, we need to advance by ten or fifteen minutes every day. And that morning light does that. And the second reason why this is very important and again, any time of day would be good because we have what we call photic history. So in other words, if you're exposed to higher amounts of light during the day, you're less sensitive to light at night. So what you're doing is you're minimizing your sensitivity to that screen at night. So if you're in a dark room all day, you might actually be more sensitive to that screen . Then if you do your walk and you get that light during the day that helps with increasing sort of your threshold for that evening light to affect your biological clock. A lot of people don't have this choice. They're actually shift workers and they're working in hospitals or in factories . And my understanding is that the disruption of their circadian rhythms is actually quite profound and has big health consequences, more so than any of this discussion about teenagers and their phon es. Yeah, I have to say my heart goes out to them because we need them . We are a twenty four hour society. We need to have nurses and physicians in hospitals and it's a very tough job . We have been doing some very interesting work . Two things. One is we have shown that red light , which does not affect the circadian system is like a cup of coff ee. It helps with increasing alertness in this population. So that helps shift workers at least stay awake and cope with trying to be awake when your body's telling you to be asleep . And the second study which we're currently finishing up and we're getting pretty interesting results is we did a lab study where we showed that if you covered one eye , instead of reducing your melatonin suppression by light by fifty percent , you actually reduce it by ninety percent . So you almost don't have suppression if you simply cover one eye . So what we're trying to do is have an orange filter which removes all of the short wavelength and allows you to still have vision in one eye and we're trying to see if that helps them with keeping them alert but not suppressing their melatonin levels. And the reason for that is shift workers are at higher risk for di abetes obesity, cardiovascular disease, cancer , and one of the hypotheses is that not just the circadian misalignment because they're basically opposite to what their body' tellsing them to do. But there's also a hypothesis that the light they're being exposed to at night is suppressing their melatonin levels . And melatonin has what we call an ongostatic effect so it helps with protecting against cancer . Given what I've heard previously about the way the blue light can influence my daily circadian rhythms and so on , it felt reasonable the idea that now we were all looking at our mobile phones and so on at night that that really was being a disruptive thing. I mean was there some kind of moral panic? Were we seizing? Were people seizing on this particular mechanism as a kind of way to explain teenagers in particular their behavior now that they have their hands on small devices and so on. I think yes, I think it would be an easy explanation. Obviously, the cell phones started , I believe before the cell phones, probably the teenagers were staying awake doing something else because it's a natural for them to stay awake . And when the phones came we could basically point to something that could be the cause of them staying awake . And obviously it makes sense to think that because we are more sensitive to blue light , it makes sense to link to the phones . But I think that we're now learning that this is not the only thing that could affect. And honestly, teenagers stay awakeing till late are things that used to happen even before the phones came up and before they were staying looking at their phones. It's annoying. I can't find it again, but I did see a headline from about the nineteen twenties saying that there's a study in the New England journal saying that children reading books at night was damaging their mental health They're always doing something wrong. Yeah, well, I think that it's so natural, especially for teenagers to tend to be more delayed and they will find something to do except falling asleep, right? And I think the phones end up being a great sort of excuse to explain something that it's a physiolog ical mechanism that happens with teenagers. In a sense the phones here of the symptom rather than the cause probably. Correct, correct. They're sort of like they got the fault for something that it's physiologically known. Mariana Figuero been, that ab'ssolute anly fascinating conversation. Thanks so much for joining us on Big Picture Science. Thank you so much for having me . Mariana Figuero is a professor and director at the Mount Sinai Lighting Health Research Center in New York . Well, Roland, that brings us to the big picture perspective in the show. Can you shine some light on what we've learned about blue light and the role of natural light on our biological clocks and on our health. Well, I'll say it's only reflected light, but reflecting on what Marianna just said, yeah , the light from your tiny little device compared to the brightness of the daylight sun, I can see that they're just chalk and cheese or I don't know whale and minnow or something . I'm sorry . Well , you know, why would your eye be sensitive to the tiny amount of blue light from your phone at night when it's actually set up to capture the warmth, the brilliance of the sun. I think that's it. Okay, what's interesting here is you're sounding certain about the latest science. I'm quite convinced . When earlier in the show, you were talking about how you thought it seemed very natural and logical that this blue light coming from our phones would affect our biology and now you're saying it seems very logical it would not affect well it's that thing a little knowledge can be a bit dangerous. I think it's the point of skeptic check is to go back and re examine presumptions that you have. So, you know, because yeah, I've been lazy. I just went along with it . Sweet dreams till sunbeams find you sweet dreams that leave all worries behind you but in your dreams whatever they be dream of a little dream We are bright eyed and bushy tailed about the talents of senior producer Seth Shostak Gary Neederhoff, Assistant Producer Shannon Rose Gary and Brian Edwards and contributors , Secon, Akbon, and Roland Pease. I'm the executive producer of Big Picture Science, Molly Bentley. Also a big thanks to our listeners and our Patreon supporters. The original music in the show is by Dewey Delay and June Miyaki. And this episode of Big Picture Science that considers what's keeping us awake at night is called Skeptic check Blue Light Special Skeptic check is brought to you thanks to a generous grant from the Trimberger Family Foundation. At the Trimberger Family Foundation, we hold that skepticism is a lamp that lights the way to truth, trimberger. org . Looking to get the most out of your money, your time, and generally give your life an upgrade? 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