If you’ve ever wondered why you can pop out of bed in the morning no problem while your partner or friend can sleep until noon, there’s actually science behind this. Meet your chronotype.
Have trouble getting out of bed in the morning? Can’t seem to get your creative juices going before afternoon? It’s probably a sign that your biological clock, also known as your chronotype—a fancy word to describe the behavioral manifestation of underlying circadian-governed biological processes—naturally starts later in the day.
“As it relates to sleep/wake cycles, a chronotype is a person’s genetic propensity to sleep at a certain time of day—independent of environmental factors—and corresponds to our circadian rhythm—our internal 24-hour biological clock,” explains Christina Kang, a certified health coach at Parsley Health San Francisco. The good news is that you shouldn’t work against or try to change your chronotype. In fact, you should lean into it. Because when you align your chronotype with your lifestyle, including your work, you’re able to sleep better at night and be more productive during the day.
What are the different chronotypes, and what do they mean?
As you might have guessed, chronotypes fall on a spectrum with morning larks and night owls on the extreme ends, Kang says. While some people have no problem waking up early in the morning and are most productive during earlier parts of the day (characterized as morning chronotypes), there are those who tend to sleep in during the morning and thrive in the afternoon and evening (called evening chronotypes.) “Some evidence suggests that morning chronotypes are associated with shorter circadian rhythm periods—less than 24 hours—while evening chronotypes may have circadian periods longer than 24.2 hours,” Kang says. (Yes, that means not everyone’s body naturally follows a 24 hour cycle.)
According to a November 2009 study in Nature and Science of Sleep, the sleep onset, body temperature, and melatonin markers for sleep are two to three hours later for evening chronotypes than morning chronotypes. Because of their delayed alertness and sleepiness rhythms, evening chronotypes can stay up later. The study also suggests that morning chronotypes often start to experience sleepiness in the middle of the day while evening chronotypes start feeling sleepy around nine hours later in the evening.
Then, there are intermediate chronotypes, which fall somewhere in between morning and evening types. These people aren’t exactly morning warriors, but they are able to wake up and go to bed earlier than evening chronotypes. To depict a comparison among chronotypes, Kang refers to Michael J. Breus, PhD, clinical psychologist and sleep doctor, who wrote a book called The Power of When, in which he describes chronotypes as animals:
- Dolphins are light sleepers and tend to have trouble staying asleep at night. Their peak productivity hours are in the mid-morning to early afternoon.
- Lions wake up early and have their peak productivity hours in the morning. They tend to get tired in the early evening.
- Bears have energy cycles that rise and fall with the sun and are most productive in the daytime.
- Wolves stay up and sleep later. They tend to start falling asleep when lions are starting to wake up.
Can your environment and lifestyle influence your chronotype?
As mentioned earlier, your chronotype is mostly determined by your genes. Kang says the human circadian rhythm is controlled by these circadian genes: period genes (PER1, PER2 and PER3) which determine your sleep drive; cryptochrome (CRY1 and CRY2); casein kinase (CK1 ε and CK1δ); circadian locomotor output cycles kaput protein (CLOCK); brain and muscle ARNT-like protein (BMAL1 and BMAL2); and neuronal PAS domain protein (NPAS1 and NPAS2).
“Twin and family studies have shown that chronotype is a heritable gene, so all of these genes are inherited. However, these genes are expressed in different ways via SNPs (single nucleotide polymorphisms), which affect your chronotype,” Kang explains. Epigenetics—turning genes on or off due to environmental factors—can contribute to your chronotype too, Kang says, but it’s still an area of research that needs more study. “For example, we know that chronotype does change with age, even though your genes don’t change. Older adults trend towards morningness,” Kang says. Children tend to be morning chronotypes too, and teenagers and young adults trend toward evening. This is due to epigenetic changes to their circadian rhythms which are closely tied to chronotypes.
That said, age, social cues and where you live can also influence your chronotype, Kang says. For example, urban dwellers are exposed to bright outdoor light for only a few hours each day, a June 2019 study in the Yale Journal of Biology and Medicine found. “In contrast, rural dwellers from pre-industrial societies are exposed to bright outdoor light during practically all hours of sunlight,” Kang says. “Light and darkness are the most powerful zeitgebers, or time givers, which are environmental cues to entrain our body’s circadian rhythm,” she explains.
A May 2018 study in The Journal of Biological and Medical Rhythm Research, which looked at the chronotype of young adults between 17 and 26 years old, suggests that having a later chronotype is associated with spending more time outside later in the day, waking up after sunrise and living further from the equator. The study also found that a later light onset and offset is associated with a later melatonin onset, hence an evening chronotype. However, it’s important to note that the study followed younger adults in school, so their light exposure differs greatly from other adults with different work schedules, which can affect circadian rhythm. Some studies also show that the seasons and the type of season at your birth can affect your chronotype. However, Kang says that due to the strong genetic component, a person’s chronotype can only be adjusted by 30 to 45 minutes based on lifestyle and environment.
How your chronotype can affect your health and sleep
Because your chronotype determines when you’re most alert or when you’re starting to feel sleepy, your lifestyle and health are significantly affected. “For example, if you don’t have time to exercise during your peak energy periods, you may not be motivated to exercise at all,” Kang says. Midday or evening chronotypes might find it particularly challenging to work out early in the morning and aren’t able to squeeze in a workout later in the day because they’re busy at work or school. This could put them at higher risk for heart disease and diabetes, among other health conditions.
Evening chronotypes are associated with a higher risk of poor cardiovascular health than morning or intermediate chronotypes, according to a February 2020 study in The Journal of Biological and Medical Rhythm Research. An older study from the same journal also found that evening chronotypes have more than double the risk for type 2 diabetes and 1.3 more times the risk for hypertension compared to morning chronotypes.
Unfortunately, many of society’s structures around work and school favor morning chronotypes over evening. “Our professional and academic culture is architected against the evening chronotype, therefore, evening types may be negatively impacted in terms of performance,” Kang says. As a result, many evening chronotypes tend to struggle with adapting to a work environment that calls for earlier hours.
“Evening chronotypes seem to have greater propensity for mental illness and tendency towards depression, bipolar disorder, and anxiety,” Kang says. Research has shown some evidence of this: A large cohort February 2017 study in The Journal of Biological and Medical Rhythm Research, which included 1,227 people diagnosed with clinical depression, suggests that depression and anxiety are more prevalent in evening chronotypes than morning chronotypes. Why? The study suggests that late chronotypes were more likely to be younger, unemployed, current smokers and have greater alcohol use than other chronotypes. In contrast, research has shown that morning chronotypes tend to have more feelings of optimism and happiness than evening chronotypes.
If you’re an evening chronotype, these studies might raise some red flags, but it’s important to understand that they don’t show an entirely accurate picture. While these studies have shown links between evening chronotypes and negative health outcomes, Kang says there are many other variables that also come into play. For instance, many of these studies don’t consider socioeconomic and health factors that can influence these negative associations.
“Trying to control for all of these variables is a herculean challenge, so the studies should be interpreted with caution,” she says. “Chronotype is not synonymous with circadian rhythm, but they are closely connected. Studies have shown that disrupted circadian rhythms are associated with negative outcomes, so that’s another variable you have to consider when you see any study correlating chronotypes with health outcomes,” Kang explains. There’s also an unhealthy user bias with evening chronotypes.
If you’re having trouble finding your ideal sleep window or syncing your behavior up to your chronotype, a health coach, like those at Parsley Health, can help you adjust your lifestyle to take advantage of your chronotype. Here, Kang shares her tips.
How to be more productive and get enough sleep based on your chronotype
Identify your chronotype
The first step in getting better quality sleep is to figure out what your chronotype is. You can do this by identifying your natural rise time and when you feel the most alert. You can also try taking this chronotype quiz, designed by the sleep doctor, Dr. Breus.
Embrace your chronotype
Once you figure out your chronotype, Kang says to embrace and own it. Then, try to sync your behavior and lifestyle with your chronotype. “For night owls, this may mean starting their work day later in the morning to maximize their sleep potential,” Kang says. She also advises scheduling important meetings and social gatherings during your peak hours.
Practice good sleep hygiene
Most importantly, you want to ensure you’re getting enough quality sleep and it starts with practicing good habits. This means avoiding electronics, such as your smartphone and the TV, one to two hours before bed to prevent impairing the onset of melatonin. “When you want to do a movie night or need to work late, consider buying blue light-blocking glasses,” Kang says. In the morning, Kang says to get direct daylight within 30 minutes of waking up by going for a walk. “And try to get that daylight signal again during the day by scheduling time into your calendar if you have to,” Kang says.
Lastly, eating a healthy diet and practicing stress management, like meditating, journaling and exercising, can help you feel more energized during the day and support quality sleep. “You’re going to be more motivated to do these things and more adept at doing them if you synchronize those activities with your chronotype too,” Kang says.
Work with your partner
If you have a partner who has a different chronotype as you, Kang recommends considering using ear plugs, a white noise machine and an eye mask to prevent disrupting sleep. “Have the incoming partner use a low-luminescent, amber-colored lamp. Casper Glow is what I use and it’s less disruptive to someone else in a dark room,” Kang says. She also says there’s no harm in adjusting your sleep time a little.
“There may be a little wiggle room with your sleep time and still be able to stay within your genetically primed window, so you can find that happy medium between two partners,” she says. And if these techniques don’t work, it doesn’t hurt to try a sleep divorce, which just means sleeping in different rooms. “This doesn’t have to be an all-or-nothing approach. Try a few nights and see how it goes. Couples tend to have a better relationship because they’re getting better sleep,” Kang says.