Developed over millennia, complex metabolic, photonic, and endocrine factors have become synchronized with environmental cues. This has occured among eukaryotes including hominids, and many invertebrates, fungi, and plants. It is the evolution of our planet that has forever linked all the animals to the seasonal and daily sun cycles, along with foraging, feeding, and most predominantly, sleeping. 
Over the past one-hundred years, humans have made it possible to disrupt the synchrony between sleep-wake cycles and our environment. Electric lights, shift work, and the constant viewing of TV or computer screens always subvert our normal rhythm. Obesity, coronary artery disease, insulin resistance, and type 2 diabetes have been partially attributed to the circadian arrhythmia arising from these technologies and lifestyle changes. 
To understand how the sun’s daily and seasonal cycles impact health and chronic diseases, we must first take note that modern bio-sciences and especially photobiology, have actually learned a great deal about the circadian mechanisms in virtually all living things. In animals and plants, cryptochromes are flavoproteins that respond to blue light by the allosteric binding of effector molecules. Humans have two such proteins, CRY1 and CRY2 which are encoded by genes of the same name, and function as circadian regulators. 
This mechanism in mammals is the period and the cryptochrome genes Per 1, 2, and 3, and Cry 1 and 2. Their transcribed protein products of those clocks inhibit their own promoters via an intricate negative feedback loop. In this way, these clocks oscillate throughout the circadian cycle, some active in the light half and some active in the dark cycle. Those transitions control important hormone secretions, such as melatonin and its mirror hormone, cortisol. The stress hormone cortisol, should be triggered by morning sunlight to start our CAR, also known as the cortisol awakening response. 
Visible light exerts powerful effects on human health because that light exposure via the retinas and, to a lesser degree, the skin, alters our circadian synchrony. Circadian rhythm is defined as changes in animals’ behavior and physiology during a 24-hour period, and the term comes from the latin words, circa dies which translates to “approximately a day.” 
The picture below explains why man-made lights, such as LEDs, are described as blue-enriched; the range of the visible blue spectrum from roughly 400 to 500 nm is clearly at a much higher amplitude than in sunlight. This would also be true of any screens used on mobile devices, computer monitors, and flat-screen televisions. 
Due to the atmosphere and the changing angle of incidence, the sun’s spectrum is modulated throughout the day: sunrise to noon contains higher intensities of “circadian” blue in the 400 – 500 nm range, and it is roughly 470 to 480 nm that initiates our cortisol awakening response in the morning. By late afternoon, the short wavelengths in blue light are scattered and the range from 600 – 700 nm predominates until sunset. This is why the later afternoon sun before sundown appears more orange and red. 
The circadian cycle can be somewhat modified by feeding, via intestinal motor neurons that are wired to the vagus nerve. Temperature also has a modest influence but the most important external phase reference for synchronizing our endogenous clock, is the sun. When our internal oscillator is “free-wheeling,” or running without its phase reference, the period of our internal cycle is roughly 24.2 hours, plus or minus some drift. When the internal oscillator or master clock, located in the hypothalamus is running in phase-lock, then the period becomes the exact sunrise to sunrise, or 24 hours each day. 
This presumes the human knows to look at the sunrise each morning, then look towards the sun throughout the day periodically, and also to watch the sunset. This prevents the oscillator from drifting as the body receives these clock “updates.” This is quite important because we have peripheral clocks derived from that master clock in the suprachiasmatic nucleus (SCN) and those local clocks control the heart, lungs, GI tract, liver, and kidneys, for example. 
This is why modern humans that live an indoor existence, or fail to see any real sunlight, and are now largely bathed in artificial lighting and blue-enriched screens all day and night, can develop chronic diseases in many different organs over time. In the last decade, there have been more research papers dedicated to making the connections between obesity, diabetes, and metabolic syndrome and circadian arrythmia caused by chronic artificial light at night, aka ALAN. 
Practicing good light hygiene, especially after dark is important because poor sleep affects health in so many ways, particularly when autophagic sleep is destroyed . In addition to avoiding ALAN, getting adequate sun exposure at the right time of year for your location creates vitamin D from good hydration and sulfated cholesterol in the skin.
Gazing at the sunrise with naked eyes, and getting sunlight on retinas and skin before 10am allows the endocrine system to receive UV regulators. UV light is a key determinant of life on Earth and mammals like us come into contact with UV via mostly skin and somewhat, via the eyes. The beneficial effect of UVB light for vitamin D levels is well known but why don’t more nutrition professionals recognize sunshine for the essential nutrient that it clearly is?
Did you know that caffeine and nicotine have carbon rings that capture some frequencies contained in morning sunlight? Those of us addicted to those two alkaloids are likely sunlight deficient and, this can be a major cause of depression, since sun exposure in the morning normally upregulates the production of dopamine in the pre-frontal cortex.
The recent discovery that the human brain also possesses vitamin D receptors (VDR), indicates that mood and depressive disorders might be influenced by vitamin D deficiency as well. The electromagnetic energy of solar radiation reaching Earth’s surface encompasses infrared, aka heat, at 700 to 1,000 nm, visible light from 400 to 700 nm, and UVR from 280 to 400 nm. All of these bands exert their controlling influences on our endocrine and neuroendocrine systems.
When exposed to sunlight, our mitochondria can make more ATP photoelectrically and our skin can produce growth hormone, nitric oxide, peptides, thyroid hormone, serotonin, and melatonin, along with the aforementioned dopamine.
To maintain proper balance for good endocrine health, it really is necessary to expose the eyes and skin to full spectrum sunlight but, if you are not a chronic sunbather, simply take your sunlight in small, frequent doses until you become acclimated to the morning and afternoon summer sun. With sufficient exposure, vitamin D binding protein (VDB) will store this hormone for the winter to maintain adequate levels all year long.
16. Karlsson, B., et al. (2005). “Total mortality and cause-specific mortality of Swedish shift- and dayworkers in the pulp and paper industry in 1952-2001,” retrieved Nov. 24, 2019 from: https://www.ncbi.nlm.nih.gov/pubmed/15751616
17. Kimball, John (2020). “Circadian Rhythms in Drosophila and Mammals,” retrieved June 26, 2020 from: https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Biology_(Kimball)/15%3A_The_Anatomy_and_Physiology_of_Animals/15.11%3A_Behavior/ 15.11.08%3A_Circadian_Rhythms_in_Drosophila_and_Mammals
41. Roberts, Joan E. (July 27, 2010). “Circadian Rhythm and Human Health,” retrieved June 27, 2020 from: http://photobiology.info/Roberts-CR.html
43. Sridhar & Sanjana (2016). “Sleep, Circadian Dysrhythmia, Obesity and Diabetes,” retrieved June 26, 2020 from: https://pubmed.ncbi.nlm.nih.gov/27895820/
About Richard Hammond
Hello, my name is Rick Hammond and I grew up in a suburb of Rochester, NY and have lived in New Jersey for thirty years. In the 70s and 80s, I was a part-time saxophonist, jazz composer and arranger while later teaching audio engineering and recording studio maintenance.
I ended up working as a free-lance engineer for fifteen years in NYC, having worked on various occasions with Rupert Holmes, The Moments, Steve Jordan, Julio Fernandez (Spyro Gyra), Bob Cunningham, and The Michael Hill Blues Band featuring Wayne Cobham and Roger Byam on horns.
In 1995 I taught electronics and the A+ Cert prep course at Computer Learning Center. Then in 2000, I became a training engineer for JVC America on their DVD, audio, and projection TV products. During this time I also began a personal chef service on weekends, cooking weekly meals, sit-down dinner parties, and outdoor dinner parties for up to 100 guests.
I also sold packaged Mexican, Italian, and American meals, salsas, and sauces from my friend’s specialty food store. However, eating what my customers ate was becoming very bad for my health so finally, I gave up my Chef for the Night and The Oniontree Cafe businesses. I now follow a high-seafood paleo-type diet that is higher in carbs during the summer but, much lower in carbs from the first frost to the spring thaw.
I had always been interested in food, health and nutrition since 1970. I began reading Adele Davis and Robert Atkins but, my health advice today is based on our evolutionary biology and seeks first to mitigate the adverse effects of our modern lifestyle and environment.
I received my Master’s Degree in holistic nutrition from HU in November of 2020. I enrolled at HU in 2013 after taking Anatomy and Physiology and Intro to Biochem at the University of Western States in 2012 to get my feet wet. In addition to seeing a few clients, I plan to write a book on quantum biology during retirement. For exercise, I still practice the Liu Seong Royal Gung-fu system which includes both Shaolin & White Crane Boxing, Ba-Gwa circle boxing, combat T’ai Ch’i, and many Indonesian fighting arts such as Kuntao-Silat.
My ancestral health and wellness website can be found at www.evolution4life.com and after my wife Susan retires from Nuance Communications, we will relocate to Rehoboth Beach in Delaware. Sue will continue writing her Rom-Com thrillers as Stella Marie Alden and I will begin writing blogs, educational articles and books on health at the subatomic level of our biochemistry, emphasizing epigenetic causes along with the Mitochondrial Theory of Modern Chronic Diseases.