Here is the full transcript of sleep scientist Christine Blume’s talk titled “How Daylight Could Help You Sleep” at TEDxBasel 2022 conference.
Listen to the audio version here:
TRANSCRIPT:
On a usual Saturday, you wouldn’t find me here. And I mean, of course, I don’t give TEDx Talks every Saturday. But what I mean is you probably wouldn’t find me in a museum. Further, if you were looking for me, you’d probably have to go to the mountains.
And that is because I absolutely love hiking. And in addition to just being outside and being in the nature, what I really like is this feeling of physical exhaustion, sort of this satisfaction you can feel in every single muscle. And in the evening when it’s time to go to bed, I absolutely cherish this amazing sleepiness that fills you from head to toe.
Now, you might say, “Well, of course she’s tired. She’s been hiking all day.” Plus, not to forget about the effects of supposedly fresh air. But there is one factor that most likely outweighs the effects of fresh air and perhaps even physical activity, and that is exposure to natural daylight.
And today I hope to convince you that we should all appreciate daylight as sort of of a natural soporific. And hopefully by the end of the talk, you will also recognize that we should all pay more attention to our daily light diet.
The Importance of Daylight
But let’s start with a question, why daylight is so important for our organism, for health and eventually for sleep. Now, throughout your body, in each and every single cell, there is a tiny molecular clock ticking inside it. And to keep these millions of clocks in sync, we have one central body clock that is located in the brain in an area which we call the hypothalamus.
And like the conductor of an orchestra, it communicates the time of day to each of these molecular clocks. And this way it is able to regulate bodily processes in sync with the time of day. For example, it causes your body temperature to increase in the morning and to decrease in the evening.
It choreographs the release of certain hormones at a proper time, and in the evening when it’s time to go to bed, it will also make you tired and sleepy. But given this precise synchronization between internal or biological time and external time or environmental time, it seems clear that the body clock cannot be blind or isolated or shut off from the environment, but rather it needs to receive information about the time of day from the environment for it to synchronize with sun time.
Photoreceptors and Light Sensing
And this is achieved by close connections between the internal biological clock in the brain and our eyes. And now you may know that in the human retina, there are different types of receptors, photoreceptors, so receptors that sense light. And classically, we distinguish two types: the rods and the cones.
Now, the rods, they only contribute to a visual impression under very dim lighting conditions. And here in the background, you now see a picture that might more or less be brought about by only the involvement of the rods. What you can see is that it’s only shades of gray, it’s slightly blurred, and around the point of fixation, which is indicated by the gray dot here, you have a little scotoma, so an area where you can’t really see anything.
Now, who recognizes what that is? Yeah? Yeah, excellent. But it’s going to be way easier, and the majority of you will recognize what it is when I now switch to the next slide, which is brought about by the involvement of the cones.
Of course, it’s the town hall of Basel, but now you can appreciate the colors, fine details, and if this was animated, you’d even see fine details in motion. But this is not the whole story. Because only fairly recently, only in the early 2000s, another type of cell has been discovered, and we call them retinal ganglion cells.
Retinal Ganglion Cells and Biological Clocks
Now, you might ask yourselves, “Well, what picture’s she going to show next?” But I have to disappoint you. I actually can’t show another picture because from all we know, these cells do not contribute to a visual impression.
But they’re exclusively designed to sense short wavelength proportions in daylight. Sometimes we also call this blue light. So they’re designed to extract important information about the time of day from the environment and pass this on to the internal biological clock in the brain.
And I guess you’ve all experienced how well this biological timing system, this connection between our biological clock and the external world or our eyes works, when we, for example, travel across time zones, because with a speed of approximately one hour per day, you can fairly easily adapt to the new time zone.
Now, how much light do we actually need? How much light is enough for the positive effects on, for instance, sleep to occur? And I have to admit, this is not so easy to answer.
The Optimal Light Environment
But I think what we have to keep in mind is that the biological timing system has evolved under the open sky and not in offices or museums. So it is also optimally tuned to the conditions we find outside.
Office light or light in rooms is in no way comparable to what we find outside. And therefore, from a scientific perspective, I can only recommend you to spend as much time as you can under the open sky, but try to make it at least 30 minutes per day.
Daylight and Sleep
Now, let’s finally talk about sleep. And I’ve repeatedly alluded to the fact that daylight is beneficial and important for sleep. And in this context, I’d like to share a little story:
So last year I had to go to hospital for surgery. And generally the hospital environment is a very challenging one for sleep because you spend way too much time in bed not moving much, you might be in pain, now and then someone comes in to check on you even during the night, and if you’re as lucky as I was, you have a snoring roommate.
And because you, of course, don’t get a lot of daylight.