It’s easy to hate clocks. Their relentless forward march wakes us up and shames us for running late. They are a constant reminder that every enjoyable moment, just like life itself, is fleeting. But even if we gathered all our time-telling devices and buried them deep in the earth, we could never escape clocks. Because we are one.
We don’t need to understand the details of circadian rhythms to know we get hungry at certain times, that the mid-afternoon slump is real, and that partying until 4 a.m. makes it hard to sleep eight hours afterward—our body clock has no sympathy for hangovers. But to better understand this all-encompassing daily cycle is to truly know our animal selves.
Most of us are awake for 16–17 hours each day, during which we never stop changing biologically. Every minute, says Debra Skene, a professor of chronobiology at the University of Surrey, “our bodies are different.” She is referring not just to our chemical makeup, bodily functions, and energy levels, but also our motivations, behavior, mood, and alertness. “At every point in time, we have rhythms that are either rising or falling. Some are at their peak, some are at their midpoint. It’s a dynamic system.”
Some of us are early-rising larks and others are night owls, because our internal clocks are unique. These different chronotypes, as they are known, are normal genetic variations, says Skene. Some people run a little fast, others a little slow; left unchecked, they would drift further ahead or behind.
“Over time, you’d be completely out of sync with life on Earth,” she says, “so the role of light and dark is critical to resetting your clock to 24 hours each day.” The light-dark cycle “is the strongest, most consistent signal that all animals have evolved to respond to.” This is why we’re becoming increasingly aware of the negative effects of too much artificial light at night: it confuses our systems, just as it does for migrating birds and sea-turtle hatchlings.
While we’re all kept more or less in line by the same 24-hour light cycle, our different chronotypes mean some of us prefer to wake up and go to bed earlier or later than others. Skene’s team found that even if a night owl trains their body clock to run two hours earlier by strictly adhering to regular waking, bedtime, breakfast, and lunch times, when they stop that training, “they might drift back to being late types,” in accordance with their internal clocks.
The circadian clock is designed to ensure survival. To do this, it needs to anticipate what is going to happen. It doesn’t respond to you waking up; it has been secretly preparing your body to wake up an hour or two before it happens. “Your cortisol hormone, which is directly driven by the master clock in your hypothalamus, is beginning to rise, so by the time you wake up, it is nearly at its peak,” says Skene. “And you need cortisol because it provides a source of glucose and gives you the courage to get up and face the world.”
Any fundamental change in your behavior as you move through the day, says Robert Lucas, director of the Centre for Biological Timing at the University of Manchester, “has to involve coordination across many different aspects of your body. So, let’s say there’s a time of day when you are likely to be hungry and looking forward to a big meal. That’s a motivational change in your brain, but you also need a coordinated change in your digestive system and your liver to predict that food is going to arrive.”
It’s your biological clock that keeps track of time and ensures everything happens when you need it. If you keep chopping and changing your routine, Lucas says: “This coordination breaks down.”Things can fall apart, and your body’s ability to predict events doesn’t work very well. We can experience this to a minor extent even when the clocks change, but definitely with jet lag. Skene’s team at the University of Surrey found that if you eat at midnight, your food won’t be metabolized the same way it would if you ate at midday, leading to higher levels of triglycerides (fat) circulating in your blood.
There’s also a whole system of alertness at play, and the battle to maintain it becomes harder the longer we’re awake. “Even if you’ve had a good night’s sleep,” says Skene, “you’ve got something counting the hours of being awake, like an hourglass. Your sleep pressure builds up all day.” But with such a long day, we need an extra boost to get us safely through the last part. So in the late afternoon or early evening, we experience a secondary peak in energy and cognitive function. “That’s our circadian rhythm in alertness,” says Skene, helping you stay awake until bedtime.
If light regulates our master clocks, wouldn’t seasonal swings in daylight hours change our behavior? Skene says: “When dawn and dusk are changing, we’ve got a bit of flexibility in the system. Animals like sheep and deer change their reproductive capacity, skin color, and body weight based on seasons. The big question we are still trying to answer is: how seasonal are humans?” It’s tricky to study, she says, because “we’ve so changed our environment, our body doesn’t know it’s dark winter out there, since we’ve got lights and heating on. So we think we’ve got the capacity to be seasonal, but the way we’ve changed our world now makes it hard to detect.”
The more holistic biologists’ understanding of the body becomes, the more juicy clues to the true complexity of our body clocks emerge. For example, the gut microbiome has its own circadian rhythm. Its daily routines interact with ours as it carries out tasks like helping to digest and extract nutrients after we’ve eaten, and making neurotransmitters such as serotonin. Even our mitochondria, the energy sources within our cells, have their own circadian rhythms, according to researchers at University College London (UCL).
Their 2019 paper, A Day in the Life of Mitochondria, showed that they “kick in really hard early in the mornings,” says Glen Jeffery, a professor of neuroscience at UCL. “They know dawn is coming when we’re still asleep.” That’s when they start generating energy, “so they’re getting you ready. This probably goes back to our evolutionary state—when you wake up early in the morning, you’re really vulnerable. Something could have been watching you during the night. You want to get up and you want to be very functional.”
Jeffery suspects mitochondria perform many other crucial bodily tasks we have yet to pin down, but we do know they have a big say in aging and death, so they’re pretty fundamental. The energy they produce comes in the form of ATP (adenosine triphosphate), a chemical present in your cells. ATP is constantly being produced and burned up. “You make your body weight in it every day,” says Jeffery. “It’s a vast process—you do not do anything in this world without ATP.” As ATP starts peaking in the morning, so does our metabolism. “Your metabolism is in a very fast state,” says Jeffery. “You may not feel like it when you crawl out of bed, but it is.”
Around midday, the mitochondria start slowing down, producing less energy, and by the evening they are much less active. Jeffery says this is why muscles can ache more after evening exercise. At night, when mitochondria-produced ATP is low, your body can produce ATP energy a second way; but, says Jeffery, it uses “this bad pathway, which is called glycolysis. Glycolysis…”This is terribly inefficient. When you go for a run late in the day and push yourself hard, leaving your muscles aching, that’s due to glycolysis. Glycolysis is like an old Ford Cortina—it gets you moving, but it produces a lot of waste. By “waste,” he means pro-inflammatory substances.
Just like our circadian rhythms, our mitochondrial body clocks are guided by sunlight. “They constantly monitor light,” says Jeffery. “What’s fascinating is that they communicate with each other. So if I interfere with the mitochondria in your toe, by the next morning, mitochondria throughout the rest of your body will know exactly what happened.”
Jeffery began his career in the Arctic, studying how animals adapt to light and darkness. He observed that during periods of constant darkness, his colleagues would not only turn on lights but also enjoyed building fires. A fire emits the same wavelength of light as the sun.
“Mitochondria act like a battery,” he explains. “You could measure their electrical charge. When that charge drops too low, they signal cell death. If enough mitochondria send this signal, the organism dies.” Sunlight helps recharge these batteries.
Earlier this year, his team published a paper showing that “if I take you outside into normal sunlight, face you toward the sun, and place a spectrometer and radiometer against your back, I can measure long wavelengths of light passing through your body, improving your mitochondrial function.” Even on a cloudy day, it might seem like there’s no sunlight, but Jeffery disagrees. In fact, he says, “The long wavelengths of light that mitochondria need are scattered by the clouds, so a cloudy day doesn’t make much difference.”
Meanwhile, Lucas’s team at Manchester is exploring the importance of daytime light and whether getting outside to maximize exposure can help counteract the confusing effects that artificial evening light has on our daily bodily rhythms.
“There’s an understanding that exposure to light in the evening and at night can disrupt these biological clocks,” he says. “But another issue is that, due to electric lighting, we now spend most of our days indoors, missing out on the bright natural light we would have experienced throughout our evolutionary history. For most people, adjusting daytime light exposure is more manageable than changing their evening and nighttime habits.” In other words, it’s easier to encourage someone to take a walk outside during the day than to convince them to give up TV or social media in the evening.
It all comes down to routine—which, Lucas notes, is highly personal, making it difficult to generalize about precise biological patterns throughout the day. “As soon as you say, ‘People sleep best at night,’ someone will reply, ‘Actually, I prefer staying awake until four.’ There are significant individual differences.” He has noticed his own routines shifting with age. “Now I’m reliably awake by six in the morning. When I was 18, I wasn’t. So these rhythms are definitely flexible.”
But the universal truth, Lucas says, “is that everyone experiences these rhythmic changes in nearly every aspect of their body.” To stay in tune with ourselves, it helps to remember the complex, body-wide changes happening beyond just our sleep patterns.What we feel in any given moment is just the surface. “You might experience sleepiness,” Lucas explains, “but beneath that, your body is preparing for many things. The same is true when you’re hungry, frisky, or feeling any of those other urges.”
Frequently Asked Questions
FAQs Unlocking Your Body Clock Syncing with Natural Rhythms
Basics Definitions
What exactly is my body clock
Your body clock or circadian rhythm is your bodys internal 24hour cycle that regulates sleep energy hormone release and other essential functions Its like a builtin schedule your body tries to follow
Is this the same as a sleep schedule
Not exactly Your sleep schedule is one part of it Your body clock influences not just when you feel sleepy but also your digestion mental focus body temperature and mood throughout the entire day
What does it mean to sync with my natural rhythms
It means aligning your daily habitslike when you eat sleep work and exercisewith the natural peaks and dips in your energy and biological functions that your body clock creates
Benefits Importance
Why should I bother syncing with my body clock Whats in it for me
Syncing can lead to better sleep more stable energy improved mood sharper focus better digestion and even support for longterm health like metabolism and immune function
Can this help if Im always tired
Yes absolutely Chronic tiredness is often a sign of being out of sync By aligning with your natural rhythms you can tap into your bodys natural energy reserves more effectively
Will this improve my sleep
Its one of the most powerful ways to improve sleep quality Going to bed and waking up at consistent times that match your bodys melatonin cycle leads to deeper more restorative sleep
Common Problems Challenges
Im a night owl Is my body clock just broken
No its not broken You may have a naturally later chronotype The goal isnt to force yourself to be a morning person but to find a consistent rhythm that works for you and minimize habits that push it even later
What throws my body clock out of sync
The biggest disruptors are irregular sleep schedules bright blue light from screens at night eating late meals lack of morning sunlight caffeine late in the day and social jet lag
