Morning and evening sleep chronotypes are often referred to as being an early bird or night owl, but according to research, larger fluctuations in circadian rhythm across people may warrant a classification for two others: the afternoon type and the napper type.
In general, differentiations between sleep chronotypes come down to when you naturally feel alert or sleepy throughout a day during which you aren’t sleep-deprived. “The word ‘circadian’ comes from the Latin ‘circa diem’ or ‘about a day.’ And the rhythm affects when you feel awake or sleepy over the course of 24 hours, as the result of hormones released in the body,” says clinical psychologist and sleep specialist Joshua Tal, PhD.
Specifically, a release of the wakefulness-promoting hormone cortisol makes you feel alert, while a spike in the wakefulness-cancelling hormone melatonin makes you feel less alert (and, in turn, more sleepy). While the presence of more natural light during the day typically drives the former and darkness at night drives the latter, both hormones may still fluctuate at different times among different people. Exactly when they do their thing is what drives a person's dominant sleep chronotype. And while that stems largely from genetics, it also varies with age and environmental factors, making an understanding of all four chronotypes that much more important.
The four sleep chronotypes
If you tend to open your eyes naturally before the buzz of your alarm, wake up early on weekends, or find it easy to transition into work mode early in the morning, you’re most likely a morning type. This means your cortisol-melatonin schedule happens earlier than average in the day: The wakefulness-promoting hormone is released sooner in the day, and the wakefulness-canceling hormone comes sooner at night, too.
This is just the opposite of the above: People who fall into this camp are frequent pressers of the snooze button and tend to struggle with grogginess in the morning; come nighttime, they usually feel more alert and stay that way for several hours after it gets dark. As you might guess, their cortisol-melatonin schedule is delayed, compared to the average: The wakefulness-promoting hormone is released later into the day, and the wakefulness-canceling hormone arrives later into the night, as well.
While the above two sleep chronotypes are pretty widely established, a 2019 study surveying more than 1,300 people about their levels of wakefulness and sleepiness at random times throughout a day identified a potential “afternoon” type, reflecting someone who is most alert in the afternoon. Like the evening types, they generally feel pretty groggy throughout the morning, but instead of a steadily rising alertness level, they have an alertness peak in the afternoon, and then get tired again around 5 p.m. and onward.
The 2019 study also pinpointed a fourth distinct sleep chronotype among people who feel sleepy at two different times throughout the 24-hour cycle—around 2 to 3 p.m., and again, around 10 p.m.—with two opposing chunks of high alertness (in the morning and in the later evening).
According to Dr. Tal, however, there’s a slight caveat: Everyone will typically feel some sort of energy slump in the mid-afternoon, reflecting a general tendency for cortisol levels to dip around that time—so, if you feel just a bit less alert then, you might not jump to the conclusion quite yet that you’re a napper type. The notable distinction here is that napper types tend to feel even sleepier in the afternoon than in the morning or the evening.
How to figure out your chronotype
Although your sleep chronotype is, again, influenced by genetics, it’s worth noting that it’s far from set in stone, says Dr. Tal. Factors like your job, lifestyle, and diet, alongside elements of your sleep hygiene can easily shift it one way or the other. In fact, a recent study analyzing sleep patterns among 3,787 people during the COVID-19 lockdown showed that when people had more flexibility to self-select their sleep timing, most turned out to be evening types—which differs significantly from previous research showing that most people (in non-lockdown conditions) are morning types.
That said, if you’d like to identify your general sleep chronotype, it’s essential to track your levels of sleepiness and wakefulness during a time in which you aren’t sleep-deprived, says clinical psychologist and sleep specialist Shelby Harris, PsyD, author of The Women’s Guide to Overcoming Insomnia. “A good way to determine your ‘sleep need’ is to do so on vacation, or whenever you don’t have specific demands, like work, impacting your sleep-wake schedule,” she says. Then, she suggests following these three steps to see if any sleep pattern emerges that may fit into one of the above chronotypes:
- Make sure there’s nothing major getting in the way of obtaining quality sleep by brushing up on your sleep hygiene (that is, limiting blue-light exposure at night, minimizing caffeine intake late in the day, dropping the temperature in your bedroom, and so on).
- Use a sleep diary to record the time you naturally go to bed and wake up each day for a week, as well as your energy level throughout the day, ranking it from zero (extremely sleepy) to 10 (high energy) each hour.
- Calculate the average total time asleep for days four to seven (as the first few days might reflect some deprivation you’re making up for). If you feel well-rested, this is your total ideal sleep need; if not, take note of particular times during the day when you felt more fatigued throughout the week, based on your diary entries.
“Even people who routinely get a good night’s sleep still have dips in fatigue and alertness throughout the day,” says Dr. Harris. “But if you have more significant periods of sleepiness that correspond to one of the chronotypes listed, you could very well fall in that camp.”
How to align your schedule with your chronotype
Once you’ve identified your chronotype, if you have some flexibility at work, you can aim to structure meetings and any blocks of time where you need to be ultra-productive around the time frames in which you know you’re most alert, says Dr. Tal. And if you can manage it, a 20-minute power nap just before an anticipated episode of sleepiness is an ideal way to thwart it, says Dr. Harris, with the caveat that it’s best to stick to just one nap a day, if possible, to avoid disrupting nighttime sleep.
If a nap isn’t doable and you need to boost alertness during a time when you're usually tired, both doctors suggest getting exposure to natural light. “And if you can throw in some gentle movement, too, with a 20- to 30-minute walk in bright sunlight, that’s even better,” says Dr. Harris.
If you’re still struggling to match your chronotype to the demands of your work or social schedule, sticking to a specific sleep pattern—that is, going to bed at the same time each night and waking up at the same time each morning, without exception—is always a helpful circadian strategy, says Dr. Tal. After all, it isn’t called a circadian rhythm for nothing.
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