Our internal “biological” or circadian clock regulates many aspects of our physiological functions and behavior, including preferred sleep times, times of peak mental performance and the coordination of physiological processes, such as when blood pressure is highest or when the heart is most efficient.
A person’s chronotype, otherwise known as circadian preference, describes their inclination toward an earlier or later sleep schedule. Although there is significant genetic variation throughout the human population, people are often categorized into “morning people” or “larks” who prefer going to sleep and waking earlier, “evening people” or “night owls” who prefer a later bed- and rising time, as well as “intermediates” who are in between these two extremes. Age, gender, external light, and room temperature can all play a role; however, genetic variation is also an important contributor. Several twin and family studies have suggested that genetic factors explain up to 50% of the population variability in circadian timing. Wherever you fall on the morning-evening preference continuum is influenced by many genes, which is what defines this trait as polygenic. This means that whether you are an “early bird” or a “night owl” is not determined by a singular gene, but rather the interaction of several, along with external environmental and lifestyle factors.
Our biological clocks are composed of specific sets of proteins, which are found in cells and tissues throughout the body. Each cell in the human body maintains its own circadian rhythm, and the “master clock” found in the suprachiasmatic nucleus (SCN) of the hypothalamus in the brain maintains synchronization of these cellular clocks. For more context, the hypothalamus’ primary function is to keep the body in stable, constant condition (i.e. homeostasis); it responds to a variety of signals from the internal and external environment by putting changes in place to correct any imbalances.
The key controller of our biological clock is a protein called Period (PER); our cells use the rise and fall of the Period protein as an indicator of the time of day, and whether or not our bodies should be asleep or awake.
Circadian rhythms and genetics
Some recent findings published by Carrie Partch from the University of California, Santa Cruz, in the journal eLIFE, found that an enzyme known as CK1 (casein kinase 1) can adjust Period levels when it binds at different sites on the protein. This results in slower or faster breakdown of the protein.
Partch and her colleagues discovered that CK1 essentially acts as a “switch”. When CK1 binds to the Period protein as it should, the switch functions normally, which generates a near-perfect 24-hour cycle. This results in people being able to easily, and correctly align their internal clocks to the daily coming and going of daylight.
If CK1 binds to the protein in a manner that causes the switch to favor a faster breakdown, the daily cycle grows shorter and less bound to daylight; this may present itself in extreme early risers, leading them to operate on a daily cycle of roughly 20 hours instead of a full 24-hour circadian cycle. This is why morning larks are considered to have an early chronotype, otherwise known as an advanced sleep cycle. In opposition, if CK1 binds to the protein in a manner that favors a slower breakdown, this will lengthen the clock, thereby predisposing these individuals to be night owls. The exciting portion of this work is that it may lead to new treatments designed to reset the clock in people suffering from sleep disorders, jet lag or night-shift work.
In a separate study conducted at Rush University in Chicago, Andrew Lim, MD and his colleagues observed 1,200 healthy 65-year-olds to investigate why older people have trouble sleeping. The researchers compared the wake-sleep behavior of subjects with their genotypes. They discovered a single nucleotide (the building block of DNA) near “Period 1” that varied between the two groups who differed in their wake-sleep behavior. At this particular site in the genome, there is a 36% chance of having two nucleotide bases termed A (adenine), a 16% chance of having two nucleotide bases termed G (guanine), and a 48% chance of having a mixture of both A and G base pairs. It was discovered that people who have the A-A genotype wake up about an hour earlier than the people who have the G-G genotype, and the A-Gs wake up almost exactly in the middle of these two groups.
Image source: The Student Scientist
The role of our brains and light
Findings from a study that performed a meta-analysis on an expanded set of 697,828 individuals from 23andMe Inc. and UK Biobank increased the areas of the genome known to influence whether or not someone is an early riser from 24 to 351; the genomic regions identified included those that are central to our circadian rhythms, as well as additional genes expressed in the brain and retinal tissue. This may indicate that part of the reason why some people are morning larks, while others are night owls, is due to differences in how our brains react to external light signals (e.g. this may suggest that the retinas of night owls are less effective at detecting and communicating light levels, resulting in poorer regulation of their biological clock).
Why you may want to reconsider your late night habits:
Through data generated from the 23andMe Inc. and UK Biobank study mentioned above, it was discovered that “morningness” is negatively correlated with both depression and schizophrenia, and positively correlated with well-being. This means that early risers were found to have lower rates of mental illness and a higher sense of personal fulfillment and happiness.
It has been recently argued through behavioral, genetic and neurobiological research that an evening preference is often associated with mild, yet chronic circadian misalignment. This disruption is suggested to contribute to aggressive behavior, as circadian misalignment has been shown to induce similar changes in many of the same brain structures that mediate aggression. Additional research has also indicated that misalignment of circadian rhythm as a result of “social jetlag” (staying up later and rising later) may be a risk factor in developing depression.
In a 2015 study, it was found that people with a late chronotype were more likely to have depression and anxiety disorders, compared to those with an early chronotype. Late sleepers also reported more mood variation throughout the day and recently, researchers have suggested that night owls have a more difficult time regulating their emotions. This 2017 study found that night owls were more likely to suppress their feelings and less likely to actively practice cognitive reappraisal (the ability to alter the way one thinks about something; i.e. “thinking on the bright side”) than morning people.
Research led by the University of Birmingham found that individuals whose internal body clock predisposed them to go to bed and wake up later (with an average bedtime of 2:30am and wake-up time of 10:15am) had lower resting neuronal connectivity in several brain regions that are linked to the maintenance of consciousness. This lower connectivity was associated with poorer attention, slower reaction time and increased sleepiness all time points between 8am to 8pm. In a separate study that recruited 56 healthy individuals and asked them to perform a series of cognitive tasks, and a physical task to measure their maximum grip strength, it was demonstrated that night owls have a larger variation in peak performance throughout the day; i.e. a night owl competing against a morning lark at 8am was more impaired than a lark competing against a night owl at 8pm.
In a research study conducted at Germany’s Aachen University that observed a group of 59 men and women of different chronotypes (16 early risers, 20 intermediates and 23 night owls), it was discovered that compared to early risers and intermediates, night owls showed reduced integrity of white matter in several regions of the brain. White matter is the fatty tissue in the brain that facilitates proper nerve cell communication; diminished integrity of this tissue has been linked to depression and disruptions in cognitive function.
Evening people have demonstrated an increased frequency of obesity and type 2 diabetes independent of sleep disturbance. This stems from evidence produced at Northumbria University, revealing that people who go to bed later tend to have unhealthier diets, consuming more alcohol, sugar, caffeinated drinks and fast food than early risers; they also consistently display more erratic eating patterns as they tend to miss breakfast and eat later in the day. Night owls were more likely to consume fewer vegetables and grains, eat less often and have larger meals in contrary. Eating late in the day was found to be linked to an increased risk of type 2 diabetes because circadian rhythm influences the way that glucose is metabolized in the body. Glucose levels are meant to naturally decline throughout the day, reaching their lowest point at night. Night owls, who often eat shortly before bed, in turn cause their glucose levels to increase when they are about to go to sleep; this may negatively affect one’s metabolism by causing the body to work outside of its normal physiological process.
In a 2013 study from the journal Chronobiology International, researchers found that evening types were 30% more likely than morning types to have high blood pressure, even after controlling for their total amount of sleep and sleep quality.
According to a 2014 research abstract in the journal SLEEP, self-described night owls spend more time sitting than people who consider themselves to be early birds. They also reported having more difficulty finding the time to regularly exercise. In addition, night owls are more likely to accumulate sleep debt throughout the work week, and sleep in on the weekends; although this strategy may appear to “make up” for lost sleep during the week, a recent paper in Current Biology revealed that sleep is not forgiving of being moved around. Those who cut down on sleep during the week, but gained additional hours on the weekend, still paid a cost of excess caloric intake after dinner, reduced energy levels, increased weight and alterations in how the body used insulin.
Research shows that you can impact your chronotype with diligent behavior change:
While some popular resources have suggested that your sleep chronotype cannot be altered, people are in fact, not fully restricted by their genetics. There is academic evidence that points to the possibility of traditional night owls changing their chronotype to morning lark through the power of choice and commitment.
Researchers from the University of Birmingham, University of Surrey, and Australia’s Monash University teamed up to see if certain techniques could shift a person’s biological clock. They recruited a group of 21 extreme night owls, who had an average bedtime of 2:30am and woke up just after 10am. The group was told to stick to the following regimens for 3 weeks total: wake up between 2 to 3 hours earlier than normal, eat breakfast as soon as possible once awakening, have lots of outdoor light exposure during the morning, eat lunch at the same time every day, do not consume caffeine after 3pm, do not nap after 4pm, do not eat after 7pm, restrict light exposure in the evenings, go to sleep 2 to 3 hours earlier than normal, and go to bed and wake up at the same time daily.
The results, published in Sleep Medicine Journal, confirmed that night owls could shift their biological clocks by two hours, resulting in earlier sleep and wake times. The participants still slept for the same amount of time, but experienced less fatigue, lower levels of self-reported stress and depression, improved reaction time, and greater grip strength (physical performance) measures.
The point made above on sleeping for the same amount of time is especially important, since waking up earlier should not come at the cost of total sleep time; if you choose to wake up earlier, it is essential to push your bedtime back to an earlier hour. If you do not, you will face the negative effects of sleep deprivation. This is the primary negative argument against being an early bird, as some people who decide to wake up early do so at the expense of their sleep duration and quality.
How to shift your cycle:
Although this research presents promising and exciting results, this degree of lifestyle modification may seem daunting to take on all at once. If you’re a night owl looking to change your sleeping habits to align with an early bird schedule, here are some simple tips to get started:
Fortunately, it is possible to reprogram yourself to become a morning person, but you will have to commit to changing a few key lifestyle factors over the course of at least a few weeks. Use the Eight Sleep app to jumpstart your sleep tracking, and begin monitoring the impact of this new habit formation.
Caroline McMorrow is a contributing writer for Eight Sleep. Caroline is a recent graduate of the University of Southern California with a Bachelor’s degree in Health & Human Science, and two minors in Performance Science and Occupational Science and Therapy. While at USC, Caroline was a research assistant at the USC Brain and Creativity Institute, primarily focused on embodied cognition, the contextual effects of empathy and the gut-brain connection.