How to optimize your circadian rhythm

Summary

Podcast Summary: Life Kit – "How to Optimize Your Circadian Rhythm"

Release Date: December 17, 2024

Introduction

In the December 17, 2024 episode of NPR's Life Kit, host Marielle Segarra delves into the intricate relationship between light exposure and our circadian rhythms. She introduces the topic by sharing her personal struggles with creating a dark sleeping environment, highlighting a common issue in modern society: excessive evening light exposure and its impact on health. Marielle sets the stage for an insightful discussion by referencing recent research and preparing listeners for expert insights post-break.

Understanding Circadian Rhythms

Marielle Segarra initiates the conversation by emphasizing the pervasive presence of light in our daily lives and its profound effects on our biological functions. She states:

“A lot of us are in this situation. In modern society, we are bombarded with light in the evenings, and research shows that can impact our health” (00:18).

Overview of the Research Study

Will Stone, NPR health correspondent, introduces a significant study conducted in the UK involving approximately 90,000 participants. These individuals wore wrist activity devices equipped with light sensors as part of the UK Biobank project. Over eight years, researchers amassed around 13 million hours of light exposure data to explore correlations between light exposure and mortality rates.

“The Researchers recruited about 90,000 people in the UK and they had them wear activity devices on their wrists. Those were also equipped with these light sensors, which meant you could track how much light each person was getting around the clock” (04:20).

Key Findings: Light Exposure and Mortality Risk

The study revealed a striking association between light exposure patterns and mortality risk. Daniel Windred, a postdoctoral researcher at Flinders University in Australia and lead author of the study, explains:

“We found that people exposed to the brightest nights had a 21 to 34% higher risk of premature mortality, whereas people exposed to bright days had 17 to 34% lower risk of premature death” (05:28).

The research demonstrated a dose-response relationship: increased light exposure during nights correlated with higher mortality risk, while ample daylight exposure was linked to reduced risk. Notably, those who balanced bright days with dark nights could potentially extend their lifespan by up to five years compared to those with bright nights and dim days.

“We estimated that people with both bright days and dark nights could be living up to five years longer than people with bright nights and dark days” (06:01).

Expert Insights: The Significance of Light Timing

Dr. Charles Seisler from Brigham and Women’s Hospital and Harvard Medical School highlights the historical context and significance of the study:

“We went from discovering that light was the most powerful synchronizer of human circadian rhythms nearly 40 years ago to recognizing that keeping our clock in sync with the 24-hour day is critical for our health and wellness and longevity” (07:05).

Will Stone elaborates on how modern societal changes have disrupted natural light cycles:

“Last one and a half centuries. We've completely changed the temporal environment to which we are exposed as a species, and we are flooding the nighttime with light that was never possible before. And we are shielding ourselves from light during the daytime” (08:29).

Health Implications of Light Exposure

The episode underscores the broader health implications of circadian rhythm disruptions due to inappropriate light exposure. These include increased risks of mental illness, cancer, diabetes, heart disease, and obesity.

“At this point, lots of research, including these carefully controlled lab experiments, show that inappropriately timed light can be hazardous” (08:45).

Practical Advice for Optimizing Circadian Rhythms

Marielle Segarra and Will Stone provide actionable steps to help listeners manage their light exposure effectively:

1. Maximize Daylight Exposure:

   • Aim for at least 45 minutes outdoors each day to soak in natural light, which is significantly brighter than indoor lighting—even on cloudy days.
   • Utilize morning light to enhance alertness, as the brain is particularly sensitive to light during this time.

   “Whenever you can get outside, try to accumulate about 45 minutes at least over the course of the day. Even if it's cloudy, you will still be getting a lot of light” (09:53).

2. Minimize Nighttime Light Exposure:

   • Use blackout curtains to darken sleeping environments.
   • Opt for muted, red-toned nightlights that don't disrupt melatonin production.
   • Avoid screens—such as smartphones and tablets—in the evening and during nighttime awakenings to prevent light from signaling to the brain that it's daytime.

   “Definitely don't look at your phone... look into those kinds of things if you want to keep your house really, really dark” (12:48).

3. Enhance Body’s Light Sensitivity:

   • Exposure to ample daylight can reduce sensitivity to nighttime light, mitigating its negative effects.
   • Developing a contrast between day and night light helps the body recognize sleep and wake times more effectively.

   “The real takeaway from this research is that you really can't think about just the day or just the night in isolation. They're really connected” (14:45).

4. Incorporate Lifestyle Changes:

   • Increased outdoor time can lead to additional healthy habits, such as more physical activity, which further supports overall well-being.

   “If you're now prioritizing getting outside a bit more to get your light, you could end up moving around more, going for a walk or a run” (15:25).

Conclusion and Takeaways

The episode wraps up with a succinct recap of the essential strategies to optimize circadian rhythms:

• Bright Days: Strive for substantial daylight exposure, preferably in the morning.
• Dark Nights: Ensure sleeping areas are as dark as possible and minimize exposure to artificial light during nighttime.
• Holistic Approach: Recognize the interconnectedness of day and night light exposure and how they collectively influence overall health.

Marielle encourages listeners to implement these changes to support their biological clocks, ultimately enhancing their health and longevity.

“Don't overthink it. Whenever you can get outside, try to accumulate about 45 minutes...” (09:53).

Final Thoughts

This episode of Life Kit offers a comprehensive exploration of how our modern lighting environments affect our circadian rhythms and, consequently, our health. By integrating expert insights and practical advice, Marielle Segarra equips listeners with the knowledge and tools necessary to harmonize their light exposure patterns, fostering better sleep, improved health, and potentially longer lives.

Transcript

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[Marielle Segarra]

You're listening to Life Kit from npr. Hey everybody, it's Marielle. You guys, I've been trying so hard to make my bedroom pitch black when I sleep, but I am fighting an uphill battle. I have blackout shades and curtains over them, but the streetlight on my block shines directly into my window and the light somehow sneaks around the edges of the barriers I've created. Also, light gets in through my living room windows and then creeps under my bedroom door. Yeah, okay, I'm being a little over the top here, but once my eyes adjust at night, it's not actually that dark in my room. A lot of us are in this situation. In modern society, we are bombarded with light in the evenings, and research shows that can impact our health when we get light and how much of it we get has an influence on all sorts of important functions in our bodies. NPR health correspondent Will Stone reported on some recent findings on this, and after the break he'll shed some light on how we should think about all of this.

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[Marielle Segarra]

Before we get back to the show, the end of another year is coming up and our team is looking back at all the tips and advice we've been able to bring you in 2024 because of your support. We've reported on everything from smart credit card habits to ditching your smartphone to napping to breast cancer screening. And it's all because listeners like you step up to support our work by giving to your local station or by joining npr. When you sign up for npr, you support our mission of creating a more informed public and get special perks from more than 25 NPR podcasts like Sponsor free listening, bonus episodes, and even exclusive and discounted items from the NPR Shop and the NPR Wine Club. Join us on the plus side [e-mail] and thank you. All right, Will, so tell us more. What about this research grabbed your attention?

[Will Stone]

This research was a pretty massive undertaking. The Researchers recruited about 90,000 people in the UK and they had them wear activity devices on their wrists. Those were also equipped with these light sensors, which meant you could track how much light each person was getting around the clock. And this was done as part of what's known as the UK UK Biobank. It's a big biomedical database that tracks information on health and lifestyle, which meant that researchers could actually follow all of these people, tens of thousands of people, over about eight years, and see who died and from what causes. And they ended up with something like 13 million hours of light data that they could use to look for associations.

[Marielle Segarra]

So these would be associations between light and your chance of dying?

[Will Stone]

That's right.

[Marielle Segarra]

Yikes.

[Will Stone]

And what they did was they'd look at the group of people who had the brightest evenings and see how their risk of dying compared with people who had pretty dark evenings. And what they found was pretty striking. I'll let Daniel Windred explain. It was his study. Windred is a postdoctoral researcher at Flinders University in Australia.

[Daniel Windred]

We found that people exposed to the brightest nights had a 21 to 34% higher risk of premature mortality, whereas people exposed to bright days had 17 to 34% lower risk of premature death.

[Will Stone]

So basically what they saw was a dose response relationship, meaning, you know, as your night got brighter, the higher risk of dying in the coming years, and then the brighter your days were, the less your risk of dying was. And wind says, you know, that risk added up if you were falling short on both ends.

[Daniel Windred]

We estimated that people with both bright days and dark nights could be living up to five years longer than people with bright nights and dark days.

[Marielle Segarra]

Okay, five years. I feel like that freaks me out a little bit. It makes me think I should be doing something differently. How concerned should we be?

[Will Stone]

Well, yeah, it's a great question. I mean, the first thing to say is upfront. This is just one study. It does not prove causation. It shows a very convincing relationship correlation between light exposure and the risk of death. I will say that they were able to control for a lot of factors that could also explain these findings, like income, physical activity, underlying health conditions. Even when they controlled for those things, they did see this clear story, which was basically, you know, you want bright days and you want dark nights. I spoke to a researcher named Dr. Charles Seisler about this study. I wanted to get his take because he's done research in this area for a long time. Seisler's at the Brigham and Women's Hospital and Harvard Medical School.

[Dr. Charles Seisler]

This is a very exciting milestone. Thinking back to nearly 40 years ago, when we first discovered that light was the most powerful synchronizer of human circadian rhythms. That was incredibly controversial and disputed to come full circle to the recognition that not only is light the most powerful synchronizer of our internal circadian clock, but keeping our clock in sync with the 24 hour day is critical for our health and wellness and longevity.

[Marielle Segarra]

It's interesting that what freaks me out is exciting to researchers. But what do you take from this?

[Will Stone]

I think the key point here is that we have these circadian rhythms, and I'm sure, you know, folks have heard about this before, these are the patterns in our biology that fluctuate, you know, approximately over the 24 hour cycle. They have enormous influence on our bodies, on our hormones, our blood pressure, metabolism. And this circadian machinery is really all throughout our body. It's in our organs, it's in our cells. But the central timekeeper, the kind of orchestrator, if you will, is in the brain. And this region in the brain responds very powerfully to light. And so obviously, for millennia, humans evolved with the natural dark light cycle. But this has changed in a big way in our modern society in the.

[Dr. Charles Seisler]

Last one and a half centuries. We've completely changed the temporal environment to which we are exposed as a species, and we are flooding the nighttime with light that was never possible before. And we are shielding ourselves from light during the daytime.

[Will Stone]

And at this point, lots of research, including these carefully controlled lab experiments, show that inappropriately timed light can be hazardous. It's linked to mental illness, cancer, especially metabolic and cardiovascular driven diseases like diabetes, heart disease, and obesity.

[Marielle Segarra]

All right, so what can we actually do with these findings? It can feel overwhelming when the environment isn't working in your favor, when there are streetlights on every corner, or maybe you have a porch light outside, or, you know, you're just inside all day working in an office and you're not getting so much daylight.

[Will Stone]

Yeah, I think this is a really important point. We have limited control over our physical environment and, you know, our lighting environment. We can't necessarily spend all day hanging out in the sun or turn out the lights promptly in the evening. But I do think there are some helpful kind of takeaways from this research and things to keep in mind that most of us can apply to our lives. The first thing is simply make sure you're getting outdoors during the day and getting the light in that context.

[Marielle Segarra]

Because the light outdoors is stronger.

[Will Stone]

Yeah, exactly. If you are in a place with tons of windows, you might be getting plenty of light during the day. But for many of us, you know, if we're in a typical indoor environment, a typical office environment, it's not a lot of light. And it's easy to kind of overestimate how much you're getting. Light can be measured in units known as lux, and you can even get an app that measures this for you. If you're curious. I have one pulled up right now. I'm sitting here in my indoor office space, which actually has quite a few windows and it's like 150 lux. And that is not very bright. As Windred explains, there's a massive difference.

[Daniel Windred]

In the light intensity between an indoor environment, which might be, let's say, 2 or 300 lux, and an outdoor environment, which might be 50,000 lux.

[Will Stone]

And this is what I heard from all the researchers I spoke to, that there's kind of orders of magnitude difference between indoor and outdoor environments typically. And so as long as you can prioritize daylight getting outside, that will help. Our brain is particularly sensitive to light in the morning. So if you can get outside, then it will help you be more alert. But even if you can't, late afternoon is fine. When you get home from work is fine. And Seizler says actually there's some evidence that being exposed to these kind of transitions in light, whether that's dawn or dusk, can be particularly important. The bottom line is, you know, don't overthink it. Whenever you can get outside, he says, try to accumulate about 45 minutes at least over the course of the day. Even if it's cloudy, you will still be getting a lot of light.

[Marielle Segarra]

All right, and what about light at night? This is obviously a big struggle for many of us. I know that for me, there are streetlights that are pretty near my bedroom window, and I feel like it can be hard to completely black that light out, even with blackout curtains.

[Will Stone]

Definitely. I have the same issue where I live. I mean, the bottom line is, the darker your night, the better you will be. In the study, people who had the lowest chance of dying in the coming years were exposed to what Windrud described as barely any light between about midnight and 6am so quite dark. On the other hand, the people who had bright light during the middle of the night, and specifically they found kind of between 2:30 and 3:00am that was associated with the highest risk of mortality. And Woodward says this is actually when your circadian system is the most sensitive to light. So, you know, if anything, at the bare minimum, make sure you're not getting bombarded with light in the dead of night.

[Marielle Segarra]

Okay, so it sounds like if you get up to go to the bathroom in the middle of the night, try not to turn any big lights on. For instance, don't look at your phone.

[Will Stone]

Definitely don't look at your phone. And actually, Seizler says they have these kind of special nightlights that are kind of a muted orange, red kind of shade, and they turn on, you know, when you walk by them, so you don't, you know, trip over, hurt yourself in the middle of the night. And he recommended looking into those kinds of things if you want to keep your house really, really dark.

[Marielle Segarra]

I've tried eye masks, too, but I feel like they always fall off by the morning.

[Will Stone]

I am not someone who can sleep with an eye mask. I think just the discomfort of having something around my face outweighs any benefits.

[Marielle Segarra]

But. Okay, so is there anything. If you are getting some light at night, is there anything else you can do about it?

[Will Stone]

Actually, there is, and this was pretty cool when I learned about this. Research suggests that making sure you get light during the day, you know, which we already talked about as being, you know, really beneficial, it can actually be protective in a way. It can reduce the sensitivity to light exposure at Night. And this comes from some studies that have measured the effect of nighttime light on the hormone melatonin. This is the hormone that promotes sleep and goes up as we get, you know, ready for bed. Scientists have found those who spend their daytime in dimly lit conditions had a much greater suppression of their melatonin when they encountered light during the night. And then that was compared to people who were exposed to more light during the day. They weren't as affected when they had artificial light at night. Now, Seizler says this isn't like a total get out of jail free card, especially if you are spending a lot of time staring at a screen before.

[Dr. Charles Seisler]

Bed, a light emitting ebook, such as a tablet or iPad or whatever, that emits a lot of blue enriched light, which sends a direct signal to the brain saying, it's daytime.

[Marielle Segarra]

I guess it's the same thing for your TV or your phone.

[Will Stone]

Yes, basically.

[Marielle Segarra]

Dang, you're taking away all my fun stuff.

[Will Stone]

Yeah, I know it can be kind of a bummer. But I think the real takeaway from this research is that you really can't think about just the day or just the night in isolation. They're really connected. This is what Laura Fonken emphasized to me. She's a neuroscientist at the University of Texas at Austin.

[Laura Fonken]

I think a really important point is not just that exposure to light at night, but also taking into consideration if you work in an office environment where you're in a cubicle where there's no windows around, you're also not getting normal daytime light levels. So then it's really that your body can't sense that contrast between night and day very well.

[Marielle Segarra]

So you want to, like, help your body out basically to know the difference between when it's time, when it's sleepy time, and when it's wakey time.

[Will Stone]

That's exactly right. And one final point that Fonken made to me, which I think is important, is that by paying attention to our light habits, you know, we may end up kind of inadvertently making other changes that are helpful for us. So if you're now prioritizing getting outside a bit more to get your light, you could end up moving around more, going for a walk or a run. And that's just one more way that our circadian rhythms and our relationship to light is really intertwined with our overall health.

[Marielle Segarra]

All right, well, thank you so much for being here.

[Will Stone]

Of course. Thank you.

[Marielle Segarra]

Okay, time for a recap. Try to keep your days bright. Aim for at least 45 minutes of time outside each day. Even if you work in a bright room, you want to head outside because the light out there is orders of magnitude higher even if it's a cloudy day. And our brains are particularly sensitive to light in the morning. So if you can get out early, that's best. Try to keep your nights dark. Blackout curtains and orange nightlights can help also reduce your screen time in the evenings. And if you get up in the middle of the night, really try not to look at your phone. For more Life Kit, check out our other episodes. We have one on everything we get wrong about sleeping and another on the importance of taking a 10 minute walk after dinner. You can find [e-mail] LifeKit and if you love Life Kit and you just cannot get enough, subscribe to our [e-mail] LifeKitnewsletter Also, we love hearing from you, so if you have episode ideas or feedback you want to share, email [e-mail] this episode of Life Kit was produced by Sylvie Douglas. Our visuals editor is Beck Harlan and our digital editor is Malika Garib. Megan Cain is our supervising editor and Beth Donovan is our Executive producer. Our production team also includes Andy Tagl, Claire Marie Schneider and Margaret Serino. Engineering support comes from David Greenberg. I'm Marielle Segarra. Thanks for listening.

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