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Circadian Rhythms: an introduction
Life has evolved around the natural light-and-dark cycles. Plants and animals have developed internal biological clocks to stay in sync with these cycles.1 These clocks allow organisms to anticipate and prepare for regular environmental changes as well as regulate and coordinate internal metabolic processes.2
Your body’s circadian rhythms are 24-hour cycles of biological, hormonal, and behavioural patterns.3 These rhythms modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, and metabolism. Ultimately, these rhythms regulate your body weight, performance, mood, and susceptibility to disease.4 At least 50% of human gene expression is under circadian control.5 As such, circadian rhythmicity has profound implications for human wellbeing and longevity.
The master conductor of your circadian rhythm is a small bundle of nerves in the
The master conductor of your circadian rhythm is a small bundle of nerves in the hypothalamus region of the brain called the suprachiasmatic nucleus (SCN).6 The SCN is directly linked to your eye. Your organs, tissues, and cells have clock genes that regulate and coordinate their biochemical processes. These peripheral clocks need to be synchronised with your master clock in the SCN to do their job well. You might be surprised to find out that almost every cell in your body has a clock that is programmed to turn on and off thousands of genes at different times of the day and night.5,7
we can now say, emphatically, that the function of our entire metabolism is dependent on light
-Prof Dr Fritz-Albert Popp
Although circadian rhythms are internal, they are entrained to your local environment by external cues such as light and temperature.8 Peripheral clocks in your gut and liver, for example, are entrained by when you eat,9 whereas clocks in your muscles are entrained by when you move.10
If the trillions of clocks in your cells are playing in tune and follow their conductor (SCN), you have a wonderfully harmonious, intricate, and resonant concert. Provided your SCN is aligned with the natural light-and-dark cycles. If a bunch of clocks are playing to their own tune, dissonance and chaos are the result. This is equivalent to inflammation and eventually leads to disease.
Your daily activities and environment are either supporting internal harmony or internal chaos. Getting the right circadian cues (light/darkness, food, exercise, temperature) at the right time is non-negotiable for a healthy body, mind, and heart.11 Setting a daily schedule that reinforces your body’s natural rhythm is the most potent health habit you can adopt. Ideally, you are nourishing, moving, and resting your body in sync with nature. Are you ready to make some changes?
Circadian can help you create a life that is aligned and in tune with the natural cycles.12 Your lifestyle and your schedule can become the source of your vitality and longevity.13 It is a matter of putting your biological schedule first.
Did you know light at night is a major driver of the worldwide increase in obesity & metabolic syndrome?
Rybnikova, N A et al. “Does artificial light-at-night exposure contribute to the worldwide obesity pandemic?.” International journal of obesity (2005) vol. 40,5 (2016): 815-23. doi: 10.1038/ijo.2015.255
Did you know light regulates intestinal balance, gut defence, repair and fat metabolism?
Godinho-Silva, Cristina et al. “Light-entrained and brain-tuned circadian circuits regulate ILC3s and gut homeostasis.” Nature vol. 574,7777 (2019): 254-258. doi: 10.1038/s41586-019-1579-3
Did you know the amount of melatonin in your bloodstream can predict the level of your immune function?
Srinivasan, V et al. “Melatonin, immune function and aging.” Immunity & ageing : I & A vol. 2 17. 29 Nov. 2005, doi: 10.1186/1742-4933-2-17
Did you know you make serotonin under ultraviolet light, increasing feelings of well-being and happiness?
Sansone, Randy A, and Lori A Sansone. “Sunshine, serotonin, and skin: a partial explanation for seasonal patterns in psychopathology?.” Innovations in clinical neuroscience vol. 10,7-8 (2013): 20-4. ncbi.nlm.nih.gov/pmc/articles/PMC3779905/
Did you know you need long-wavelength red/infrared light to regenerate your retina? What is missing in modern light sources and screens?
Albarracin, Rizalyn et al. “Photobiomodulation protects the retina from light-induced photoreceptor degeneration.” Investigative ophthalmology & visual science vol. 52,6 3582-92. 1 Jun. 2011, doi: 10.1167/iovs.10-6664
Did you know light at night can suppress your melatonin levels by 80%?
Wright, H R, and L C Lack. “Effect of light wavelength on suppression and phase delay of the melatonin rhythm.” Chronobiology international vol. 18,5 (2001): 801-8. doi: 10.1081/cbi-100107515
Did you know grounding reduces pain and improves sleep?
Ghaly, Maurice, and Dale Teplitz. “The biologic effects of grounding the human body during sleep as measured by cortisol levels and subjective reporting of sleep, pain, and stress.” Journal of alternative and complementary medicine (New York, N.Y.) vol. 10,5 (2004): 767-76. doi: 10.1089/acm.2004.10.767
Did you know ageing is associated with desynchronisation and decreased expression of circadian rhythms?
Lax, Pedro et al. Photosensitive Melanopsin-Containing Retinal Ganglion Cells in Health and Disease: Implications for Circadian Rhythms. International Journal of Molecular Sciences vol. 20,13 (2019): 3164. doi.org/10.3390/ijms20133164