Have you ever wondered how our bodies know it’s time to wake up? Or how we get tired at around the same time each night, why jet lag takes such a toll on our bodies, or why we feel that afternoon slump around 3 in the afternoon? We can blame all of this on our body’s circadian rhythm, or internal biological clock. Running 24 hours, 365 days a year, our bodies are programmed through various hormones and environmental changes to keep a 24 hour routine. Changes such as jet lag, blue light, sunlight, and seasonal impacts (like that 4pm sunset in the winter) can have various effects on our body’s processing, in both good and bad ways! Keep reading to learn more about the science behind circadian rhythm and how you can tick-tock your own clock into working more effectively.
What is the Circadian Rhythm?
The circadian rhythm is defined as physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes, found all throughout nature, respond primarily to lightness and darkness. An easy example of this is the sleep-wake cycle; we sleep at night and are awake during the day. Our biological clocks are the timing devices that dictate most of our lives. From our behaviors and digestion to heart rate and fatigue, we are always on this 24-hour clock. In fact, the word circadian comes from the Latin phrase “circa diem”, which means “around a day.”
What is the Circadian Rhythm made of?
Our circadian rhythm is a physical structure, made of molecules, known as proteins, that interact with every cell in the body. Almost all body tissues and organs contain their own biological clocks, and all of these work in sync to help us throughout the day. The “Master Regulator” is in the region of the brain called the hypothalamus. It’s composed of 20,000 nerve cells (aka, neurons) and coordinates all of the smaller biological clocks. The hypothalamus receives direct input from the eyes; this would explain why those living in colder climates get tired so early in the wintertime. When our eyes sense darkness (or lack of light), our bodies become programmed to sleep way earlier than our normal bedtime. This would also explain why so many of us benefit from sunlight first thing in the morning–our eyes sense the light and our body’s clock is kicked into gear to get our body ready for the day ahead.While other cues, like exercise, eating, social activity, and temperature, can affect the master regulator, light is the most powerful influence on all circadian rhythms.
How do Circadian Rhythms affect our health?
Most of us know that a peaceful night’s sleep doesn’t happen every night. Whether we’re stressed, sick, mentally burnt out, or jet lagged, an interrupted or poor sleep can have significant impacts on our overall health. Without proper signaling from our body’s internal clock, we can have a hard time falling asleep, staying asleep, or waking up in the morning. Thus, our total sleep time is reduced and/or our sleep routine can be thrown off, leading to shallower, split and lower-quality sleep. Overall, a misaligned circadian rhythm can negatively affect sleep in so many ways. From an increased risk of insomnia to falling asleep at our desks at 3PM, getting enough high-quality sleep is imperative in ensuring we rest, digest, and wake up feeling refreshed. If you’re having trouble falling asleep, Calm by Arrae can help. Simply take 2 to 3 capsules before bedtime and drift off into a deep, restful sleep.
Hormones are tiny chemical messengers that impact our whole body. From serotonin (our feel-good hormone) to melatonin (the one that makes us sleepy) our body is in a constant flux of hormone regulation. Hormones like melatonin and cortisol increase and decrease alongside our circadian rhythm. While melatonin is released at night and suppressed during the day, Cortisol makes us more alert and helps our bodies to wake up in the morning. In case you’ve heard that Cortisol isn’t good for us, check out this blog post for some Cortisol myth-busting.
Eating Habits and Digestion
Other nutrient-sensitive hormones, like ghrelin and leptin are also impacted by our biological clocks. Ghrelin tells our bodies when we’re hungry; this is why some of us wake up wanting breakfast ASAP and get hungry for lunch and dinner around the same time each day. However, releasing ghrelin at night would be a bad thing–all of us would wake up in the middle of the night to eat! Leptin, on the contrary, tells us when we feel full; it’s released after meals to signal to our brains that we can stop eating. All in all, both of these hunger hormones are in control of our feeding cues and metabolic state.
Acetylcholine, one of our primary neurotransmitters, is released during wakefulness and diminished during sleep. It’s responsible for contraction of our muscles, dilation of blood vessels (to allow blood to reach our organs), increasing bodily secretions (think sweating during a workout) and slowing our heart rate. Acetylcholine is the main regulator of alertness, attention, learning, and memory, hence why its functioning is so crucial during the daytime.
Mood, Anxiety, and Depression
An irregular circadian rhythm can have various negative health effects, including decreased quality of both sleep and cognitive functioning. Furthermore, when our biological clocks aren’t working as they should be, mood disorders, especially anxiety and depression, are more likely to develop and be symptomatic. Studies that aim to find correlation and causation between sleep and our internal rhythms often focus on shift workers, whose sleep periods are often opposite the ‘norm’ due to sleeping during the day and working throughout the night.
In terms of anxiety, it’s unclear in the literature whether anxiety causes shifts in the circadian rhythm or vice versa. Researchers believe that a disrupted rhythm can cause a lack of or poorer quality of sleep, therefore affecting functioning the following day. A cycle occurs when a decline in functioning affects sleep, and so on. The basis of the research shows that having a regular sleep-wake cycle is key in keeping anxiety at bay.
A misaligned circadian rhythm is highly correlated to depression; one meta-analysis showed that night shift workers are 40% more likely to develop depression than daytime workers. Much like anxiety, the same situation occurs in depression: those with depression often have changes in their sleep patterns, hormonal rhythms, and body temperature control. It’s been found that, because those with depression more often experience severe symptoms first thing in the morning or right before bed, the severity of a person’s depression correlates directly with the degree of misalignment of his or her circadian rhythm.
These impacts show the importance of having solid morning and night routines. By working with, not against, our hormones, we are giving our bodies what they need to live optimally, and happily! Getting direct sunlight right upon waking, or using bright light therapy, have both been found to assist in the regulation of this rhythm and, as a result, a decrease in negative mental health symptoms.
It’s also worth mentioning that other factors, such as physical activity, stress and anxiety, lifestyle habits, and age play a role in the formation and maintenance of our circadian rhythms. Not to worry, creating and maintaining proper circadian rhythms can be done easily. As we’ve said before, it’s all about routine.
Follow a consistent sleep schedule: Try to sleep and wake up at or around the same time every day (yes, even on the weekends!). Our bodies struggle to maintain a sleep rhythm if one day we sleep at 9PM and the next at 1AM. Find a happy medium between your usuals and stick to it.
Get daily exercise: Any form of working out, even a walk to get your favorite coffee, helps support our daily clocks by releasing endorphins and making it easier to sleep at night.
Avoid caffeine: We hear you: coffee gets us up and out of bed each morning. However, curb your caffeine intake after noon; caffeine keeps us awake and throws off our natural cycles.
Limit light before bed: It may seem like this trend is popular, and that’s with good reason! Artificial light, or blue light, can trick our body’s into believing it’s daytime, hence decreasing our willingness to sleep. Experts recommend not using devices 30 minutes before bedtime, but if you absolutely must, invest in a good pair of blue light glasses.
Gnocchi, Davide, and Giovannella Bruscalupi. “Circadian Rhythms and Hormonal Homeostasis: Pathophysiological Implications.”MDPI, Multidisciplinary Digital Publishing Institute, 4 Feb. 2017, https://www.mdpi.com/2079-7737/6/1/10/htm.
Lawrence Epstein, MD, and MD Syed Moin Hassan. “Why Your Sleep and Wake Cycles Affect Your Mood.”Harvard Health, 13 May 2020, https://www.health.harvard.edu/blog/why-your-sleep-and-wake-cycles-affect-your-mood-2020051319792.
Silver, Natalie. “Circadian Rhythm: What It Is, How It Works, and More.”Healthline, Healthline Media, 30 Mar. 2022, https://www.healthline.com/health/healthy-sleep/circadian-rhythm#how-it-works.
“The Connection between a Disrupted Circadian Rhythm and Anxiety.”Chronobiology.com, 19 Feb. 2019, https://www.chronobiology.com/the-connection-between-a-disrupted-circadian-rhythm-and-anxiety/.