When was the last time you saw the sun rise or set? Think back to the last time you were in nature. How did you feel? Today we are seeing an enormous amount of emerging research on the benefits of being outdoors and specifically the importance of light on our circadian rhythms.
Did you know your circadian clock is an actual part of your body? And not just a single part of your body, but part of a system tied to nearly every cell and bodily function.
Biological Clocks
Composed of genes and proteins, your biological clock constitutes an intricate series of interacting molecular pathways throughout your body that operate in a feedback loop.1 Each unique gene and protein regulates specific functions in almost every single cell in your body.2 These clocks are found in nearly every tissue and organ. And not just in your body, biological clocks exist in almost all organisms including plants, fungi and bacteria.3
There are a three main types of biological clocks:4
- Circadian Rhythms: the term circadian comes from Latin. The Circa meaning “around” and Diem meaning “day.” That’s because circadian clocks and rhythms refer to cycles that operate daily on a nearly 24-hour loop such as sleep-wake cycle.
- Ultradian Rhythms: cycles with shorter loops such as blinking, heart rate and bowel activity.
- Infradian Rhythms: cycles that last longer than 24 hours. Examples are menstruation in humans, vernalization in plants and hibernation or migration in animals.5
The Master Clock
Located in both the right and left hypothalamus (found in the brain and behind your eyes) is your master clock. Here we find a pair of distinct cell groups of roughly 20,000 nerve cells (neurons) called the suprachiasmatic nucleus (SCN).6 This is the body’s central clock and it resynchronizes itself daily with stimuli such as light via the optic nerve. The SCN orchestrates all the circadian rhythms in an organism, keeping your body in harmony.
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Circadian Rhythms
Our biological or circadian clocks work in tandem with our master circadian clock to coordinate what we call circadian rhythms. Circadian rhythms are physical, mental and behavioral changes that flow in a daily sequence. These rhythms include the wake-sleep cycle, hormone production, hunger and digestion, temperature, brain wave activity, mood, stress, heart function, cell regeneration and immunity.7 Two key determinants of circadian rhythms are that they are endogenous (self-sustained) and entrained (adjusted) by external stimuli called zeitgebers (German for time giver). Some zeitgebers include temperature, exercise, food, and light.
While biological clock refers to a variety of both short and long cycles, circadian refers to daily cycles that occur within a 24-hour period. In fact, two studies released this year have established that some circadian rhythms occur at specific times of day. New research from McGill University shows that T cells (white blood cells; key players of the immune systems) are more likely to activate at specific times of day.8 While another study went a step further and established that the time an influenza infection occurred directly correlates to the molecular response and outcome of the illness.9 This knowledge is currently being applied towards drug efficacy, since many drugs, including chemotherapy, function optimally when administered at a specific time of day.10
Circadian Dysfunction
Two studies from the University of California, Irvine in collaboration with Institute for Research in Biomedicine in Barcelona, Spain were released this past May. In these studies, researchers shut down the entire circadian system of mice (including the brain), except for two distinct clocks in the liver and the skin. The results showed that the liver’s circadian clock could detect light from skin alone. Only when subjected to total darkness did the liver’s clock stop functioning. Late night artificial light could activate the liver’s circadian clock, throwing rhythms out of balance.
The senior author of these studies Paolo Sassone-Corsi has also conducted earlier studies revealing that sleep deprivation, artificial light, exercise and diet can all rewire our circadian clocks leading to health concerns including depression, allergies, premature aging, and cancer.
We are just beginning to establish a powerful connection between sunlight, artificial light and the function of our circadian clocks. A variety of studies have now clearly established that blue light can disrupt sleep cycles.11 Just earlier this year, two separate murine studies also established the impact of blue light on aging12 as well as blood sugar levels.13 Clock dysfunction is now being connected with a variety of diseases and disorders including seasonal affective disorder, insomnia, diabetes, depression, bipolar disorder, and obesity to name a few. Which shouldn’t be all that surprising considering that these cogs in the clocks of our human body regulate so many crucial components of daily life.
Emerging research is also demonstrating the power that sunlight14 and being in nature15 can have on health. A 2017 study of women demonstrated that participants who spent time outdoors in the morning not only slept better, but also had more consistent daily routines and more optimally functioning circadian systems.16
With daylight savings behind us and winter ahead of us many of us regress into a pattern of snuggling up indoors and hibernating. But, it’s important to remember the value of fresh air and sunshine. Not only does sunlight play an important role in your circadian health but even as little as 15 minutes of sun can boost your vitamin D levels.17 A short 15-minute walk outside can improve concentration, reduce stress18 and improve cognitive functioning.19 Plus, physical activity releases endorphins which boosts energy and lifts mood.20 Yes, we know it's cold outside. But bundle up. Go stand in the sunshine. Breathe in fresh air. Get outside and adventure in nature. It’s good for your health.
1 https://earthsky.org/human-world/cool-facts-about-your-biological-clock
2 https://www.sciencealert.com/your-body-has-trillions-of-clocks-in-its-cells
3 https://phys.org/news/2012-05-group-circadian-clock-common-life.html
4 https://www.healthline.com/health/biological-rhythms
5 https://learn.genetics.utah.edu/content/basics/clockgenes/
6 https://www.biointeractive.org/classroom-resources/human-suprachiasmatic-nucleus
8 https://www.phillyvoice.com/circadian-rhythms-immune-system-study-body-clock-t-cells/
9 https://www.nature.com/articles/s41467-019-11400-9
10 https://www.nature.com/articles/d41586-018-04600-8
11 https://www.ncbi.nlm.nih.gov/pubmed/30311830
12 https://www.sciencedaily.com/releases/2019/10/191017101253.htm
13 https://www.sciencedaily.com/releases/2019/07/190709091120.htm
14 https://www.healthline.com/health/depression/benefits-sunlight#benefits
16 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5587264/
17 https://www.healthline.com/health/depression/benefits-sunlight#mental-health
18 https://www.advancedneurotherapy.com/blog/2015/09/10/walking-outside-brain
19 https://www.huffpost.com/entry/tk-ways-fresh-air-impacts_0_n_5648164
20 https://www.health.harvard.edu/mind-and-mood/sour-mood-getting-you-down-get-back-to-nature