What is Your Circadian Rhythm (And How Does it Impact Your Health)?

Key takeaways:

• Circadian rhythms are physical, mental, and behavioral changes the body undergoes within a 24-hour cycle.
• Your sleep-wake cycle is a circadian rhythm that is influenced by external factors, including light.
• A circadian rhythm disruption can affect your sleep, focus, and health, but there are ways to get it back on track.

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We all run on a clock. Maybe you rely on an alarm clock to wake up in the morning. Or you use the clock as a cue for meals or bedtime, hitting the pillow when it strikes 11 pm. But even if you never look at the time again, your body will know to rise with the sun and get sleepy when it sets. Why? The answer lies in the body’s internal clock or circadian rhythms, which are physical, mental, and behavioral changes the body experiences in a 24-hour cycle. Circadian rhythms dictate your sleep schedule, body temperature, appetite, and hormone levels.

Circadian rhythms are ruled by a master clock in the suprachiasmatic nucleus (SCN), a structure located in the hypothalamus in the brain. The SCN regulates various circadian rhythms in your body. Clock genes in the SCN signal processes to occur throughout the day, including the most well-known one: the sleep-wake cycle. 

Factors that Influence Circadian Rhythms

Your circadian rhythm is an internal clock controlled by genes and hormones, but external factors can also affect it. Those are:

• Light: The SCN is influenced by exposure to sunlight, which is why our sleep/wake cycle is aligned with darkness and daylight. While sunlight is the major regulator of your circadian clock, research suggests that artificial blue light, such as those emitted by tablets and smartphones, may also influence your circadian rhythm. The extent of their impact, however, remains unclear. We do know that late night technology-related behaviors, such as gaming, computer or phone use, increase brain alertness and delay sleep, and thus, may have a greater impact on our circadian clock than the light emitted by the devices.
• Meals: The hormone insulin, which helps move glucose into the bloodstream for energy, follows a circadian rhythm, peaking during the daytime and hitting its lowest point in the early morning. Eating off-schedule (say, a late-night snack) can affect this circadian rhythm.
• Exercise: Research has shown that exercise can help regulate circadian rhythms. A review in Frontiers in Pharmacology suggested that circadian rhythm is influenced not only by the timing of exercise but also by duration, intensity, and volume. The researchers found that two hours of moderate exercise in the afternoon or night delayed the onset of melatonin, but the melatonin peak time was unchanged by those who exercised in the morning. 
• Stress: Cortisol, a.k.a. the stress hormone, peaks in the morning when we wake because it helps us feel more alert. It decreases during the day and gradually increases while we sleep. Chronic stress can cause spikes in cortisol that disrupt this natural rhythm.
• Your daily routine: Work (especially shift work), school, and even your social interactions can all affect your natural rhythm depending on the time of day (or night) they’re scheduled. 

What Happens When Your Circadian Rhythm is Disrupted

When your circadian rhythm is out of sync, you can experience symptoms ranging from fatigue to health issues. According to the National Heart, Blood, & Lung Institute, these disruptions may be short-term and caused by factors such as jet lag from travel or a new work schedule. Or, they could be long-term circadian rhythm disorders caused by aging, genetics, and certain medications.

If your circadian rhythm is out of whack, you may experience:

• Sleep issues: When your circadian rhythm is not aligned, you may experience delays in falling asleep, frequent wake-ups, insomnia, and poor-quality sleep overall.
• Cognitive performance problems: Sleep-related issues can lead to trouble focusing, memory issues, and difficulty staying on task.
• Fatigue or lack of energy
• Mood changes: A misaligned circadian rhythm and lack of quality sleep can lead to stress and depression.
• Weight gain: Research in Nature Reviews Endocrinology revealed that poor sleep and a misaligned circadian rhythm are metabolic stressors associated with weight gain and obesity.
• Health issues: Circadian rhythm disorders have been linked to several health conditions, including diabetes, obesity, high blood pressure, heart, and gastrointestinal problems.

How to Realign Your Circadian Rhythm

If your circadian rhythm is disrupted, there are several things you can do to get it back on track.

• Be strategic with light exposure: Light is a key regulator of the circadian clock and can help adjust your circadian rhythm. Exposure to bright sunlight in the early morning can help advance your circadian clock, making you sleepy earlier in the evening and waking up earlier in the morning. Bright evening light, on the other hand, will delay the clock, causing you to become sleepy later and waking up later.
• Set a sleep schedule: Sticking to a consistent bedtime and wake-up time can help, especially if you’re a shift worker with an unavoidable circadian rhythm disruption. You can use a schedule to get back to normal after jet lag, incrementally adjusting your wake or bedtime.  
• Understand your natural circadian rhythm: Try sleeping without an alarm clock for a few days to see when you naturally wake up.
• Reduce caffeine and alcohol: Both can delay bedtime or affect sleep quality, especially when consumed in the evening.
• Create a healthy sleep environment: A cool room with dim light and no devices can help foster a good night’s sleep. 

See your physician if you’re experiencing prolonged sleep issues, severe fatigue, and other health symptoms.

Help Elysium Understand the Science of Sleep

Introducing the Translational Initiative to Map Epigenetics in Sleep (TIME-ZZZ), a new study designed with sleep expert Russell Foster, Ph.D., to help us better understand the connection between sleep quality, chronotype, mental health, and biological aging. 

If you’ve ever taken an Index test registered through Elysium Health, you can participate by answering a series of short questionnaires (called activities) covering topics on sleep quality and mental health benefits. Participants receive study insights, including their chronotype, and contribute to advancing clinically validated interventions and health monitoring tools for longevity.

Sign up for TIME-ZZZ here and find additional study details on clinicaltrials.gov under the identifier NCT06333301.