Here we see an early bird and a night owl in their natural habitats. The early bird rises with the sun, springing out of bed abuzz with energy. As the day goes on, they slowly get more and more exhausted until finally crashing around sunset. Meanwhile, the night owl rises long after the sun, stumbling groggily from their bed. After about 30 minutes— or a cup of coffee— they begin to come to life. But they don’t really hit their stride until later in the day, at which point they comfortably coast past sunset, only heading to bed in the early hours of the morning. For many, this is a familiar story, and one that’s easy to cast yourself in. But how many people are truly night owls or early birds? And are our natural sleep schedules predetermined at birth, or can we change them?
The truth is there’s a lot of space between these extremes, and most people fall somewhere in the middle. These behaviors are determined by our circadian system— which is anchored by a pair of nerve cell clusters located in the anterior hypothalamus. These nerve cells respond to light exposure coming in through your eyes to track the day-night cycle that dictates your body’s internal clock, or circadian rhythm. That steady rhythm helps determine the body’s flow of hormones, with the broader circadian system acting like a conductor that keeps your organs functioning in time with one another. And a major part of that performance is managing the body’s transitions between being awake and being asleep.
Now, your circadian system can't just decide its bedtime and knock you out. However, by tracking how much light you typically get and when in your waking hours you usually get it, the system can make predictions about when you’re likely to need sleep and prepare your body accordingly. For example, if you consistently go to sleep around 10 pm, your circadian system will start producing sleep-inducing melatonin around two hours before then to tell your body it’s time for bed.
So if this rhythm is molded by our sleep habits, can we change it just by sticking to a strict schedule? To a degree. Everyone’s bodies are unique, so even two people with the same sleep schedule might have different experiences based on their circadian system’s hormonal quirks. For example, where early birds generally flood with cortisol just before waking up, night owls often have their cortisol peak roughly 30 minutes after getting up. Hormonal differences like these determine how you experience your circadian rhythm. And while these factors can shift with age, you’re unlikely to grow out of your body’s preferred sleep schedule.
That said, you can cultivate habits to help or hinder your circadian rhythm. Keeping consistent sleeping hours helps your body accurately predict when to send out hormones, making it easier to stick to your schedule. Conversely, research in sleep deprived college students has found their unpredictable sleeping habits weaken their entire circadian system. Compromised circadian rhythms are less effective at coordinating organ functioning and can incur health risks like metabolic disorders and vulnerable immune systems. But perhaps just as important as sleep hygiene is light hygiene. Getting sufficient contrast between bright daylight and dimmer nighttime light is essential for synchronizing your circadian rhythm, and nothing establishes this contrast better than sunlight. Even on overcast days, sunlight is much brighter than standard indoor lighting. So if you're typically awake during the day, try getting outside as soon as possible to teach your body when to be active and alert.
It’s difficult to maintain a sleep schedule that pushes against your body’s preferences. And even if you succeed for months, it only takes one bad night to send your circadian system back to baseline. But whether you’re an early bird, night owl, or somewhere in between, it’s important to remember that as long as you’re consistent, there’s no wrong time to wake up or go to sleep. What matters most is getting enough rest for the day ahead.
