Sleep plays a critical role in supporting both mental and physical health. [1,2] When it comes to promoting optimal health and longevity, achieving adequate, high-quality sleep is an important factor.
But does it matter when you sleep? Humans vary in their chronotype—the tendency to wake up earlier in the morning or stay awake later into the evening. Some identify as more of an “early bird” and others more “night owl.” Is one healthier than another? Read on to find out.
Key takeaways:
Circadian rhythms are the physical, behavioral and psychological changes that occur in the body over a 24-hour cycle, corresponding with the 24 hours of lightness and darkness on Earth. In humans, the circadian rhythm is directed by the suprachiasmatic nucleus, or SCN. The SCN is considered the body’s “master clock” and is housed in the “control center” part of the brain called the hypothalamus. It receives input from the environment (ie. exposure to light) and the body (ie. food intake or physical exertion) to coordinate hormone production, metabolism, and body temperature throughout the day. [3]
While all humans share a similar circadian rhythm (none of us are truly nocturnal, for instance), there are measurable differences between those who prefer waking earlier or staying up later into the evening. [4]
Chronotype refers to this preference. Research suggests that while there are some people who have strong “morningness” or “eveningness” tendencies, most people fall somewhere in the middle. [5]
Chronotypes that align with the circadian rhythm are associated with better health outcomes and reduced risk for metabolic disease. [6] Alternatively, a wake and sleep pattern that is out of sync with biological circadian cues—so called “chronodisruption”—is implicated in increased rates of chronic disease. [7]
Here are a few specific examples of how chronotype can affect your health:
Individuals with a preference for staying up later into the evening are more likely to report poor sleep quality, inadequate sleep time, and irregular sleep patterns than those with morning or intermediate chronotypes. [8] Evening chronotypes may consequently be more vulnerable to depressed mood, increased anxiety and increased perceived stress. [9]
Compared to those who prefer waking and eating earlier in the morning, evening types are more likely to skip breakfast, eat later into the day, choose less nutrient-dense foods (people often eat more packaged snack foods than whole grains and veggies late at night) and tend to have higher BMIs. [10,11,12]
In general, research suggests that those with a stronger preference for “morningness” tend to have better metabolic outcomes than those who prefer to stay awake later into the evening. [12]
Your chronotype may impact your athletic performance. Morning types tend to perform better in the morning, while evening types need to be awake for a longer period of time in order to reach their peak performance. One study of athletes found that evening types needed 5.5 more hours of awake time than morning types in order to perform their best. [13]
Even for non-athletes, the optimal time to exercise depends on chronotype, too. One study found that evening exercise was more likely to disrupt the circadian rhythm in morning types (though it had a positive effect for evening types). [14] This study also found that exercising in the morning had a positive impact on both evening and morning chronotypes.
Those with evening chronotypes are more likely to experience something researchers call social jetlag. Social jetlag occurs when individuals dramatically shift their sleep/wake cycles on work or school days compared to their work-free days – like waking up at 6:00 am Monday through Friday, then sleeping in until 12:00 pm on the weekends to make up for lost sleep. [15] The phenomenon also occurs when morning or intermediate chronotypes work night shifts. Social jetlag is associated with impaired academic or work performance, poor mental health, and unhealthy lifestyle behaviors. [16]
One study found suggested (but not statistically significant) hormonal differences between morning and evening chronotypes, with morning types experiencing a slightly earlier rise in estrogen and later chronotypes experiencing a later surge in luteinizing hormone. [17] Another study of women with PCOS found that having an evening chronotype predicted more severe insulin resistance. [18] And in a population of post-adolescent males, one study found chronotype may be influenced by testosterone and that high testosterone led to stronger eveningness. [19]
Chronotype is at least partially hereditary, and corresponds to genetic differences in circadian regulation. There are currently over 300 identified genetic markers that affect someone’s potential to be a morning person. [20] One of those markers is the DNA marker Per3 – studies have found that this gene marker predicts a 10% increased likelihood of being a morning chronotype. [21]
Most research looking into chronotype differences use validated questionnaires, like the Morningness-Eveningness Questionnaire (MEQ). This questionnaire asks hypothetical questions about your preferred time to wake, perform activities of daily living, exercise, and sleep. Depending on your responses, you will be sorted into one of five chronotypes: “definite evening,” “moderate evening,” “intermediate,” “moderate morning,” or “definite morning.”
Other websites offer similar quizzes to sort you into a chronotype category similar to a personality test. Clinical psychologist and author Michael J Breus, PhD is cited with creating the animal-based chronotype categories: Lion, Bear, Wolf and Dolphin. [22]
Emerging technology can also provide individualized information about your chronotype. Wearable devices like the Oura Ring offer insights into your actual sleep length, quality and timing. Genetic analysis, like Inside Tracker’s genetic potential score, can even identify markers in your DNA that predict morningness and eveningness traits.
Even though a predisposition for a certain chronotype is encoded in your DNA, it doesn’t appear to be an unmodifiable trait.
For one thing, chronotype changes throughout the lifespan. Adolescents trend toward eveningness, while older adults trend more toward morningness. [23,24] Chronotype may also be influenced by latitude and exposure to light, so where you live can play a role. [25]
Some research suggests that targeting light exposure, meal times, caffeine intake and exercise may help to shift “night owls” toward an earlier wake and sleep cycle, improving perceived mental health, stress, cognition and physical performance during typically “suboptimal” morning hours. [26]
Much of the existing research suggests that people who wake up earlier in the morning have better health. This is likely because their wake and sleep pattern aligns with their innate circadian rhythm. Folks who wake up earlier in the morning tend to have a more biologically-appropriate exposure to light, eat a healthier, more balanced diet at consistent intervals, and enjoy higher quality, sufficient sleep. [27]
Understanding your chronotype can help you identify which of these behaviors to focus on in order to feel your best:
Research suggests that exposure to blue-enriched light in the morning or upon waking can help support circadian alignment and boost alertness throughout the day. [28] On the other side of the same coin, reducing exposure to blue light and instead using dim, orange to red-tinted light supports melatonin production and improves sleep quality at night. [29]
In research, evening chronotypes tend to engage in more unhealthy behaviors like smoking, drinking alcohol, skipping meals, and eating late at night. [9,30] These are all common ways that individuals may attempt to cope with feelings of stress and anxiety. Healthier coping mechanisms—like exercise, social connection, and therapy—can help to reduce the risk of chronic disease. [31]
The circadian rhythm is responsible for coordinating digestion and function of the gastrointestinal system. [32] Eating to support your circadian rhythm means eating within two hours of waking, and then at consistent intervals—about every three hours—thereafter, or in response to your body’s hunger signals. Research indicates that getting the majority of energy and nutrition from food before 3pm is associated with improved markers of metabolic health including: [33]
Regardless of chronotype, quality sleep remains an important predictor of overall health and wellbeing. Bedtime and wake times that align with your circadian rhythm are more likely to lead to better quality sleep, and better health. [34] When worn at night, wearable technology like the Oura Ring can track your sleep and give you personalized data about sleep duration, sleep disruptions, sleep cycles, and resting heart rate, so you can learn what bedtime and wake time works best for your body.
Your chronotype can have health implications, and knowing your predisposition can help you determine whether to consider prioritizing lifestyle habits to optimize your sleep and metabolism.
InsideTracker’s genetic analysis provides insight on your genetic potential for morningness—though multiple factors including lifestyle, work schedule, and preferences all help influence your actual chronotype. Combining data from genetics with blood biomarkers and wearable devices that you can sync through InsideTracker’s app (including Apple Watch, Garmin, Oura Ring, and Fitbit), you can take scientifically-supported targeted approaches to optimize your healthspan.
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