What happens to our bodies without light?

Vox

01-03-2025

In a Cold War-era bunker-turned-Airbnb situated 50 feet below ground in Arkansas, journalist Lynne Peeples conducted an experiment to better understand her internal clock. She'd always struggled with sleep — growing up in Seattle, the long, dark winters contributed to the effects of seasonal affective disorder (or SAD). From an early age, she says, she understood her circadian rhythms — the body's measure of time that drives everything from the sleep-wake cycle to appetite — were generally disrupted.
For 10 days, she cordoned herself off from all of the signals the body uses to tell time. She deprived herself of light, from both the sun and electricity, clocks, most screens and other people. (Peeples did have some light: She set all the LED lights in the Airbnb to a dim red light, which wouldn't impact her circadian rhythms.) She strapped herself up to devices that tracked her temperature, glucose levels, sleep, and heart rate and tried to live as normally as possible. To pass the time, she juggled, played the harmonica, and read on a Kindle. She documented her experience on a typewriter.
About halfway through, her internal clocks had completely flipped. Her stomach was 'distant and grumbly,' her chest heavy, and she had a general weak and woozy feeling. Unbeknownst to her, when everyone above ground was sleeping, she was wide awake. Later, while combing through her biometric data with scientists, she discovered her rhythms had fallen out of sync with one another. 'I could feel it,' Peeples says. 'I was feeling all the symptoms of sleepiness throughout the day, hot and cold at odd times, a little bit of depression. I'm not thinking clearly. My gut was a disaster. All those things happened about the same time.'
Peeples recounts the experience in her book The Inner Clock: Living In Sync With Our Circadian Rhythms , in which she digs into the science of circadian rhythms and explains how understanding our body's ebbs and flows can help us feel better when we're awake and asleep. Here, Peeples shares what she's learned and how you can better calibrate your own circadian rhythms.
This interview has been edited and condensed for clarity.
Were there any surprising takeaways from your experiment in the bunker?
These inner clocks we have in our bodies are not precision timekeepers. That's why we need these regular recalibration opportunities with the light-dark cycle of our planet. But they are pretty good clocks. The first couple days, I was living pretty close to a 24-hour day without having any idea what the actual time was. I would occasionally make a guess at the time for fun, and a day-and-a-half in, I was only off by 11 minutes.
So why is light so important to our internal clocks?
We evolved outdoors. The sun, during the day, shines a full spectrum of light, and it's centered around the blue wavelengths. We evolved these cells in the back of our eyes, these photoreceptors, that perceive that blue light and send signals to our master clock in our brain that says, I see this strong blue light. It must be daytime. That's how we evolved to tell day from night.
In today's society, a lot of us in the modern world, we're hidden from both bright days and dark nights.
In today's society, a lot of us in the modern world, we're hidden from both bright days and dark nights. We're losing that contrast that we evolved with. Not only do we have this relatively dim light during the day, but we also have basically that same light indoors at night too, when we're sitting under light. It's really about that contrast that our clocks evolved to use to differentiate day and night.
Should we be trying to get more of that contrast? So, making it dim in our houses when the sun goes down and trying to get bright light during the daytime?
I would say yes. This is what I'm trying to do. Especially in the morning, if you can get outside for 15, 20 minutes of actual daylight, that really helps recalibrate your clocks and keep them synced to the 24-hour day. During the day, get outside for little bits, even if it's cloudy out, and inside, try to be close to a window.
Then at night, dim the lights. Try to use warmer hues of light. The oranger, the redder the better. In my apartment now at night, I turn off all overhead lights. I'm only using table lamps and electric candles that I have around my apartment. As you get into later evening, if you're going to bed, try to cut out absolutely every light. If you have to get up in the middle of the night to go to the bathroom, do not slip on the bathroom lights. A warm night light or carrying a candle is the best plan.
I often hear the advice of getting light in the morning. Can SAD lamps effectively mimic that light?
If you have the option to get outside, that is still the best because you can get out for a walk and that's good for you. But if you don't have that option and it's the dead of winter anywhere at a high latitude and there's not even the sun up in the morning, then SAD lamps definitely have their place.
On the flip side, how concerned should we be about blue light from our electronics?
To some degree, certain things can be overblown. The overhead lights in your apartment are probably having a bigger impact on you, especially compared to a TV. Because at that distance, that blue light coming from the TV is probably minimal if you're not right up against it. If you have an iPhone, if you dim it, it's not probably producing that much harmful light. The consensus among scientists is that blue light can have an impact on our sleep, on our rhythms. The extent of that impact is still up for debate. It can't hurt to try to limit that, but to a point. You don't want to cut out all your pleasure in your life. If you're watching something that's calming, that helps turn down your brain a little bit to help you sleep at night, the benefits may outweigh the risks.
Are there 'ideal' times of day to be doing certain tasks based on our circadian rhythms, like exercise in the afternoon, or thinking hard in the morning?
There are certain times a day, depending on your personal chronotype or how your circadian rhythms run, when you are going to be at your best for thinking, for solving a problem, for running faster, for lifting more weight, for being creative. On average, the science suggests that late morning hours are usually the best as far as your alertness. For me, I do fall into that category. Since I've learned that, I do try to use those hours to tackle my more challenging mental tasks. Then as far as physical performance, on average, most of us are at our best in the late afternoon or early evening. That's when most world records are broken for swimming, for example. It is personal, so you have to get a sense of your own rhythms to be able to time these activities.
On average, the science suggests that late morning hours are usually the best as far as your alertness.
How can we figure out when we might be better suited to certain tasks, short of locking ourselves in a bunker?
The best thing to do is when you're on vacation, let your body tick as it will. Go to bed when you're tired, get up without an alarm, when your body naturally wakes up. Then just pay attention. When am I feeling most on ? When is that dip in the day? A lot of us have that afternoon dip and that's part of the circadian rhythm, but that might fall at a different time for different people. When do you have a spring in your step and feel like running? Try to see if you have some wiggle room to allow yourself to to follow your body's schedule as closely as you can.
What practical takeaways would you give people as far as how to make sure that their systems are running efficiently?
There are three key things. The first I talked about was contrast: trying to get those bright days, those dark nights.
The second thing is what I call constrict. That has to do with eating, as well as caffeine and alcohol. Try to consolidate the hours during the day that you eat and concentrate your calories earlier in the day. Late morning, early afternoon, for most of us, is when our bodies are most able to handle incoming calories. It's the opposite of what modern society does. We tend to have our biggest meal in the evening. Try to get calories earlier, and try to cut off calories two, three hours before bed, ideally. With alcohol, if you're having a drink, have it more at happy hour than post-dinner.
Finally, consistency — trying to go to bed and get up at the same time every day. There's been more research that's come out saying the consistency of the times you go to bed and get up in the morning, seven days a week, can be more important than how long you sleep. See More: Advice
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