Dr. Samer Hattar

My pleasure.

So, I mean, you do appreciate the effect of light for vision.

So when you wake up in a beautiful area, beautiful ocean, light is essential.

The sunrise, the sunset.

So that's your conscious perception of light.

But light has a completely different aspect that is independent of conscious vision.

And that's how it regulates many important functions in your body.

I think the best that is well-studied and well-known is your circadian clock.

And the word circadian comes from the word circa, which is approximate, and DN is day.

So it's an approximate day.

Why is it an approximate day?

Because if I put you or any other human being who have a normal circadian clock in a constant conditions,

with no information about feeding time, about sleep time, about what time it is outside, you still have a daily rhythm, but it's not exactly 24 hours.

So it will shift out of the solar day because it's not exactly 24 hours and hence the name circadian.

It shows up at every level that we know we studied.

It shows up at the level of the cell.

It shows up at the level of the tissue.

And it shows up at your behavior.

The most obvious for you is your sleep-wake cycle.

You sleep and you're awake and sleep at the 24-hour rhythms.

The period length of the sleep rhythm on average is 24.2 hours.

So you'll be drifting 0.2 hours every day.

out of the solar day if you don't get the sunlight.

So the sunlight adjusts that approximate day to an exact day.

So now your behavior is adjusted to the light, dark environment or the solar day.

It's part of the brain that is not consciously driven.

So you actually do not know when it happens or when it doesn't happen.

And that's what we'll get into when I tell you why light affects your mood and why sometimes people don't know how to deal with light to improve their mood, for example.

So let's do the math.

If you shift out 0.2 hours a day, in five days, you're shifting out one hour.

So you're literally one hour off in your social behavior in five days.

In 10 days, you're two hours off.

And if you're an organism that is living in the wild, shifting out of the right phase of the cycle, you could either miss food or you could become food.

So it's really essential for survival.

I think it's one of the strongest aspects of survival for animals to have the anticipation and the adjustment to the solar cycle.

Yeah, so we knew that in mammals, including us, we are mammals, humans, that the eyes are required for this function.

So if humans are born without eyes or the optic nerves are damaged, humans are not able to adjust to the solar cycle.

So we know that the eyes are required.

In the human retinas, there are two types of photoreceptors.

They are called rods and cones because of their shapes.

And these rods and cones simply take the photon energy, which light is made of, and they change it in a way to an electrical signal that allow us to build the image of the environment in our cortices.

However, people have found, including me with the work of David Burson and Ignacio Provencio, that there is a subset of

of ganglion cells.

The ganglion cells are the cells that leave the retina, their axon, leave the retina, and project to the brain.

So these were thought to only relay rod and cone information from the light environment to the brain.

We found that a small subset of these ganglion cells are themselves photoreceptors that were completely missed in the retina.

And these are the photoreceptors that relay light environment subconsciously

to the areas in the brain that have and house the circadian clock or the circadian pacemaker, which adjusts all the clocks in our bodies to the central brain clock, that allows them to entrain to the 24-hour light-dark cycle.

In fact, they possibly have no problems in circadian photoentrainment.

They'll have enormous sleep-wake cycle.

But they're totally blind.

But they are totally image blind.

And what's really interesting is that, and this story I heard from Chuck Seisler, so I'll give him credit, that some of these people who are image blind, usually they get dry eyes and they give them a lot of pain.

And

Doctors used to think, oh, since they are image blind and they're getting dry eye, why don't you just remove their eyes?

They're not using them anymore.

And the minute they would remove their eyes, they start having cyclical sleep problems indicating that now they are not in training to the light-dark cycle and are having cyclical jet lags when their clock shifts through the light-dark cycle.

Honestly, I think the easiest thing is waking up.

Get as much light as you can.

Into your eyes.

Yeah, it's really nice.

Your system is primed.

If you're entrained, it's primed to get light.

The sun should be out.

Even when it's cloudy, you're going to get enough intensity to help you adjust your cycle to the day-night cycle.

These are general rules of thumb, but how long do you recommend people go outside?

If you do it daily, I would say 15 minutes.

If you don't do it daily, you may want to increase it.

You do it more, it doesn't hurt.

And I'll tell you, if you're sensitive, you don't even have to go in the sun.

You could be in the shade.

There's going to be so many photons out there in the shade.

It's going to be perfect.

Yeah, honestly, this is where we don't have a lot of information still, because this is where we're going to discuss this maybe in more detail, that if you put humans in artificial conditions, the circadian system is very sensitive to light.

But in reality, in the real environment,

light also is affecting other aspects that are independent of the setting of the circadian pacemaker.

And these which we call the direct effect of light on mood, for example.

So that is very hard to figure out what intensity you need to use.

And we haven't done enough experiments because the system has been discovered just recently.

But yeah, I mean, honestly, if you're that far north and you're in the winter and you want to make sure you don't use these light boxes, I would suggest that personally.

Daily is the best.

This system is really about...

And you'll see that even for the effect on depression, it's about multiple days.

So you don't have to worry if you missed it one day, stay longer if you want.

But if you're in a hurry and you want to do other stuff, that's a great recommendation.

And you saw this during the pandemic.

A lot of people mentioned that their sleep-wake cycle suffered a lot.

Because if you're not going out and if you're staying at home and you don't have big windows and you're waking late, waking up late, and then you're using very bright light till late at night, your body's going to shift.

And now your day is going to start instead of like really when the sun comes up, let's say at six o'clock in the morning,

your day is going to start at 11 o'clock in the morning.

That's what your body is going to think is the beginning of the day.

So then you're not going to be able to sleep at 10 o'clock at night because now that's really, for your body, is completely different timing.

So there is great data on this, and there is a couple of things that complicate this.

The first is

The people who usually are late.

What do you mean?

People that wake up late and go to sleep late?

Go to sleep late and wake up late.

They have an overwhelmingly higher level of depression because human notice that people who go to sleep early and wake up early, they do better in life.

They notice that.

They just perform better.

They perform.

But the question is, is that intrinsic to the system or is that society?

Because society start things usually early or late.

That's a hard question to ask.

We discriminate against late risers.

In a way, we discriminate.

And I'm not so sure that the circadian system is that variable in the human population.

I mean, clearly there are maybe some genetic factors that make a small percentage of like everything with a bell shape.

But I think most of the time, the light environment may play a role.

And once, as we've talked about, this is a long-term effect of light.

Once you get into a rhythm,

It's hard to break out of that rhythm because if you start sleeping late and waking up late, you're not getting the morning sunlight.

And so you're just going to be late.

I mean, the best thing to do is to let the natural light creep in into darkness, right?

That would be the best.

But clearly that would be inefficient.

You want to go home, you want to read, you want to talk to your kids, you want to talk to your family.

So I think

it's nice to extend the day.

I don't think that's wrong if you somehow can block that light from affecting your circadian clock.

I am an extreme, but I measured it for myself and I asked Reji, my wife, if she's okay with it.

She also liked the dimness.

Both of us can see well in dim conditions, but I think you have to measure it for yourself.

You really have to do, it's a very simple experiment.

Just try to dim the light as much as you can.

I call it the minimum amount of light you require to see comfortably.

You know, use red light that is very dim if you want to keep the room for sleeping.

Red light that is very dim has very small effect on circadian clock.

And below 10 lux of red light literally doesn't affect sleep at all.

So if you just look on the side, most of the light is going to go this way and you're only seeing this.

And even when I check sometimes, I check it so fast and switch it off so fast.

So ideally, I should not check.

iPhones and iPads.

I don't use iPad at night because it's hard to lower it enough because it's huge.

But even my iPhone, I try not to use it at night.

I mean, eventually, because we're talking about the whole system, eventually when you start having the other problems, you also develop sleep problems, but you're absolutely right.

And in fact, now research from Diego Fernandez in the lab have found that now we know that they actually require different brain regions.

So we don't only have a theory,

We don't only have a light environment that showed they can be dissociated.

We know that they use completely different brain regions.

So the SCN that I told you about earlier, the place where the central pacemaker is, the one that receives direct input from the retina through the IPRGCs to adjust your circadian clock,

is not the area that receives the light input for mood regulation.

It's a completely different brain region.

And what's really amazing, this region also receives direct input from the IPRGCs, but projects to areas in the brain that are known to regulate mood, including the ventral medial prefrontal cortex, which has been studied for many years to be impacted in a human depression.

So just by this amazing serendipity to find that a region that is so deep in the advanced brain, like the prefrontal cortex is your executive brain, one of the most elaborated in humans, to see that they receive input from these ancient photoreceptor was stunning to us.

So that's why we came up with the tripartite model, because as a circadian biologist, I only thought of light through the circadian clock affecting behavior.

As a sleep biologist, they only thought of the homeostatic drive affecting sleep, affecting behavior.

And for people who study light for vision and other things, they thought only of the environmental input.

But now if you put them all together, you get with this tripartite model where it's really mind-boggling and it makes so much sense.

The organism doesn't want to depend on a single component.

But if you could incorporate these three together, you could have a beautiful system that is well-adapted.

So let me tell you the sleep-wake cycle, right?

So we know there is a homeostatic drive to affect sleep.

We've had beautiful talks about that.

Which is basically the longer you're awake, the more you want to be asleep.

So that's your homeostatic drive.

We've talked about the circadian influence of sleep and the fact that light-dark cycle affect the circadian system, which eventually affects sleep.

So these two components are well understood.

Now, the third factor is your direct light or environmental input.

How much stress, how much light you get from there also can highly impact sleep.

So even if you have a good circadian and homeostatic drive, if you're getting light at the wrong time of the day or if you're being stressed and thinking, then your sleep is going to suffer.

So you have to think of the three together to have a beautiful sleep-wake cycle.

So now that I've told you about all these interactions between the different inputs to the circadian clock,

Just you think about it as an engineer, what would be the best thing?

The best thing is to know when your food times happen in the day, when should you get light, and when is your circadian clock in your system?

So if you eat at very specific times of the day, that's another signal that is telling your body, your clock, you're in a certain time of the day.

So if you're having lunch at the correct time every day and you're getting bright light, now you have two systems that are informing your clock.

your clock is gonna be better.

So regular mealtimes.

Regular mealtimes that fit your circadian clock.

And in fact, if you do that, when I started doing this, and it helped me lose weight, is that I'm exposing myself to the right amount of light-dark cycle.

I'm eating at regular time.

It is amazing.

You will be not hungry, let's say you eat at noon.

You will not feel any hunger at 11.45, and then all of a sudden, the hunger subsides.

This is clearly not an energy issue because it could not be that drastic.

If that's the time.

And it depends if you also do multiple meals.

Remember, three meals, that's a decision that somebody came up with.

I don't know why.

Yeah.

Right.

I mean, so you could have two meals.

You could have...

very multiple meals that are distributed across your active time.

As long as they don't eat early in the morning.

That's just, you have to work with your schedule, with your active schedule.

And the nice thing, as you said, finding them out is going to help you to understand how they interact because we know from the tripartite model that they are all interconnected.

And for each person, they're going to be interconnected differently.

I mean, honestly, this is my moonshot.

This is the thing that I think people, because I say don't take a pill, take a photon.

I mean, you take pills.

It's important.

I'm just making it that really we have an opportunity right now with the incredible advances of LED lights, of changing spectra of light, of regulating intensities.

And just for simple changes, you could really improve sleep-wake cycle, productivity, and still you could actually get more done.

Because as we've talked about, when you have all these messed up, now you have to sleep more, but your sleep is fragmented.

It's not very good.

And you can't focus when you do today.

And you can't focus when you don't have alertness, when you need the alertness.

So having all these could allow you to do even more actually at the end than less.

And that's the exciting part of it.

So it's very simple as we've talked yesterday.

So imagine you're in the outside with no industrial light.

If your body thinks you're in early evening and you see a bright light, what does this tell you?

Oh, wait, this is not early evening yet.

It's still early afternoon or late afternoon.

So I have to delay my clock to go back to late afternoon.

So if you get light early in the evening, it delays your clock.

So what does- Meaning that makes you want to go to sleep later.

Yes, it delays your clock.

So later in the night, later in your night-

And actually, it just happens that in humans, you get a temperature in the deer later in the night, low temperature in your body.

After that, lights start advancing your clock.

Yeah, because then your body thinks, oh, it's seven o'clock, so it'll advance your clock by one to two hours.

Absolutely.

But you have to remember the light, right?

So let's, now that we explained it very simply, let's take a very simple example, right?

New York to Italy.

That's a simple example.

New York time, Italy time, six hour difference, right?

So let's say you fly from New York at night.

You reach Italy at eight o'clock in the morning.

What is the time in your New York time?

Although you reach- Six hours back.

Six hours back.

It's 2 a.m.

It's 2 a.m.

So when you land Italy, you want to avoid light like the plague.

Yeah, you could eat, but you really don't want to get a light.

Because otherwise it's going to delay you.

It's going to delay you.

It's going to send you to California instead of sending you to Italy.

It's very important.

to avoid getting the wrong light information when you're trying to adjust your body because otherwise it shifts you to the other side.

Absolutely right.

I really agree with you that I think part of the reason I'm continuing to be able to do this, that I really think about it and I make sure that I keep everything aligned.

And that actually helps me a lot.

Like I don't suffer in sleep.

I don't suffer in waking up.

I never use a timer to wake up.

System is so aligned, it works.

Yeah, I mean, it is possible.

Or it's possible that their clock is completely misaligned, that they are getting maybe enough time at night when they are supposed, and then they possibly feel so sleepy in the

So all these are possible combinations.

A nap, or the weaker part of the sleep.

I mean, you see this when you travel to different time zones before you adjust.

You go to sleep really well, but two hours later, you're fully up.

Two hours.

If you were so tired and this is your regular sleep, there's no way you're going to wake up in two hours.

Honestly, you could see it perfectly, I think, in Scandinavia.

I mean, you could talk to people who live in.

Sure.

They get seasonal depression.

What seasonal depression is one, but actually when you start asking them questions, they tell you like in the winter, they barely could wake up.

They barely have the energy before even depression.

Even people who don't get seasonal depression, they'll tell you our energy level is lower.

Our ability to go to work is not the same.

And in the summer, most people actually sleep very little.

They tell you we really can...

We feel like we're manic.

We have all this energy and not in a negative way, in a funny way, right?

I mean, but if you want to sleep, we have to put this curtain.

I think in these situations, you could really appreciate the seasonality of humans.

I think we kind of destroyed our seasonality because we don't get exposed

to that much natural light.

We have all this artificial light.

But I think honestly, one of the thing that is gonna happen if they follow your recommendation, this is gonna cause them to also experience some changes across the season, because now they're gonna see the sun differently.

If you're gonna go out in the morning,

In the summer, you're gonna get a much brighter.

That's why I don't like the change in time.

I know people think, oh, because you're biased.

Because I think- Wait, wait, wait, wait.

Sorry, the change in time.

Are you talking about daylight savings?

Daylight saving.

It's such a bad idea because it disrupts that rhythm that you're having.

Because I think your body, if you keep that rhythm, you will see the whole seasonality.

And I look at it from a different aspect than other people.

If you think about it, Andrew, there is a situation where you're getting light perfectly well, and then all of a sudden they delay it by one hour.

And then even though it's the summer, your body now, if you're still not adjusting, think, oh, wait, what happened?

What kind of happened?

And when it's so close, it's sometimes hard to figure out how to adjust it perfectly because we're already sleep deprived in our society.

And then you shift it by, so it just, it all accumulates and it has no benefit.

I just don't understand why they do this.

It makes no sense.

is pushing people to get even later in the summer when light is going to push you later anyway.

It's at Samer Hattar.

And I think the same for Instagram.

Yeah.

And light.

Yeah.

Awesome.

Thank you, Andrew.