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Sleep Chronotypes 101: How Your Genes Decide the Ultimate Bedtime

Life is organized in circadian rhythms according to your internal 24-hour biological clock, which means that many physiological processes have a clear diurnal (daytime) rhythm which is innate in humans and other animals. To put it simply, we do some things at night and some during the day. This is reversed in species said to be nocturnal – who get moving when the sun goes down.

A sleep chronotype is your genetic propensity to sleep at a certain time of day and corresponds to your circadian rhythm1. Natural variation exists amongst the human population regarding each chronotype, but generally, individuals are often separated into:

  • Morning people (“larks”) who prefer going to bed and waking earlier
  • Evening people (“owls”) who prefer a later bedtime and later rising time
  • Intermediates who are between the two extremes

Interestingly, your chronotype also influences appetite, exercise, health, and core body temperature. We report on sleep chronotype as part of our custom nutrition plans.

Do our chronotypes change over time?

Generally, most children have an early chronotype, which is why it’s so hard to sleep in as a new parent! However, beginning in adolescence, the chronotype becomes later which has led to the assumption that teenagers are lazy because have difficulty waking up in the mornings, when in fact, it’s a change in their biological clock that is occurring.

The chronotype then gradually starts to shift earlier beginning from the age of 20. Most middle-aged American adults report a bedtime between 11 pm and 12 am, and a wake-up time between 7 am and 8 am. As the individual ages further, the chronotype shifts even earlier2.

What is your chronotype?

The Sleep Doctor, Michael Breus, has broken down the chronotypes even further and claims that if you determine your chronotype, you’ll become more energetic and less tired during the day. He claims that if you experience fatigue and find it difficult to wake up in the morning, you probably don’t follow the daily schedule of your chronotype.

He divides the chronotypes into four main categories:

  • Dolphins – light sleepers and tend to have trouble staying asleep at night. Their peak productivity hours are 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 – energy cycles that rise and fall with the sun and are most productive in the daytime, found in about 55% of the population.
  • Wolves – stay up late and sleep late. They tend to start falling asleep when lions are starting to wake up. They make up approximately 15% of the population.

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 as well as the time of day when you feel the most alert.

Your chronotype has a genetic component

Research shows that chronotypes have a strong genetic component. Although multiple factors play a role, having a specific allele on the PER3 circadian clock gene3 has been tied to being an early riser.

It has been suggested that the reason there are variations in chronotype may date back to the hunter-gatherer era and served as a survival technique. The theory is that by taking turns sleeping, there would always be someone awake to keep watch around the clock.

Different chronotypes are associated with certain personality traits

Emerging evidence suggests that certain chronotypes possess personality traits that are dependent on whether you’re a morning or evening person.

This came to light in a study that found an association between the extraverted personality factor and the PER3 clock gene. This gene is a major regulator of your circadian rhythm and determines how long you sleep. Researchers took this a step further to determine whether there is in fact a link between chronotypes and personality characteristics.

In a study that assessed 2,492 individuals, extraversion, agreeableness, and conscientiousness were related to being an early riser, whereas being open to experiences and neuroticism were related to night owls 5.

Chronotypes and dietary habits

The association of chronotypes with other factors has gained traction and has shown that your chronotype may also affect your eating habits.

In a study done in adolescents, the researchers found that later bed and rise times were associated with the tendency to drink caffeinated drinks, eat fast food but consume fewer dairy products. They concluded that morning-oriented pupils exhibit a healthier and more regular lifestyle6.

Chronotypes and exercise timing

Exercise has been prescribed as a non-pharmacological, low-cost treatment option for disturbed sleep. However, some researchers have raised concerns regarding the timing of exercise; finding that late-night exercise results in sleep-inhibiting conditions.

A study assessing 909 college students found that evening exercisers had later bedtimes, poorer sleep quality, and lower sleep efficiency compared to morning exercisers. They are also reported greater daytime dysfunction compared to morning chronotypes7.

So, if you’re an evening chronotype, it’s probably best to avoid exercising in the evening as this may worsen your functioning during the day.

Lockdown affected our chronotypes during the COVID-19 pandemic

The lockdown implemented by many countries during the COVID pandemic left us spending day after day indoors.

Researchers hypothesized that this reduced our sunlight exposure significantly and disrupted our daily social schedules which affected our circadian rhythm.

A study looking at 1021 subjects found that participants slept longer and later during lockdown weekdays and had lower levels of social jet lag. While this may seem to have been an overall improvement in sleep conditions, the chronotype was also delayed among these individuals8.

They found that younger subjects experienced larger changes in sleep and chronotype than older subjects. Also, subjects who began to work from home, or those who stopped working slept more and exhibited later chronotypes compared to those who continued working outside during lockdown.

A different study showed that when people had more flexibility to self-select their sleep times, most turned out to be evening types—which differs significantly from research conducted before lockdown showing that most people are morning types10.

Chronotype and Health Outcomes

The assessment of chronotype and its relation to overall health has gained attention since a growing body of evidence has highlighted the health hazards that are related to shift work, especially night shift work 9.

Health hazards have been more common among the “night owls” than among the “early birds,” such as:

  • mood disorders
  • anxiety disorder
  • substance use disorders
  • personality disorder
  • insomnia
  • arterial hypertension
  • type 2 diabetes
  • infertility

Alarmingly, current data suggest that “night owls” tend to die younger than “early birds”. These associations are so common that the routine assessment of chronotype as part of health status examinations in healthcare settings has been suggested in order to limit or curb the effect that possessing this chronotype has on overall health.

While the science behind chronotype is often confusing and complex, if you’re struggling to determine your chronotype, the best strategy is to keep a routine of waking up and going to sleep around the same time every evening. Remember that being a Wolf or a Dolphin isn’t the same as experiencing chronic insomnia and if you’re experiencing symptoms of insomnia, it’s a good idea to see a doctor and discuss potential external causes for your sleep problems.

Dr. Gina Leisching

Dr. Gina Leisching holds a BSc in Functional Human Biology, and Honours degree in Physiological Sciences, as well as a doctorate in human physiology from Stellenbosch University, South Africa. At Gene Food, Dr. Gina uses her expertise to provide evidence-pieces that readers may find helpful and informative.

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