Blue Light And Your Circadian Rhythm
July 02, 2020
July 02, 2020
Whether we realize it or not, all life is inherently organized around the daily and seasonal rhythms of natural light. These predictable and consistent cycles create order, meaning, and most importantly energy, allowing for complex life to thrive throughout the natural world.
Humans, in particular, are profoundly impacted by the presence or absence of light. Our bodies are programmed to use the sun’s dynamic electromagnetic spectrum as a barcode for critical behavioral and physiological processes—these daily changes are referred to as our Circadian Rhythm. Almost every process is tied to the circadian mechanism at some level, making proper alignment with nature critical to optimal health.
The challenge in the modern world, however, is the widespread use of non-native, artificial blue light in our homes, workplaces and technology. While it certainly makes our lives more convenient and productive, our constant exposure disrupts our circadian rhythm, altering critical functions throughout the body. The result is dysfunction and chronic disease, which have become unfortunate norms.
What Is The Circadian Rhythm?
The term circadian rhythm was first coined by Franz Halberg to describe the cycle of biological processes lasting roughly 24 hours1. The presence of a circadian mechanism is an important feature of most organisms, allowing them to adapt physiologic functions to environmental signals for optimal energy production and expenditure2. Processes like metabolism, glucose, body temperature, cognitive performance, hormonal balance, and mitochondrial activity are all tied to our circadian rhythm and must be aligned with nature to function optimally.
How Does It Work?
The circadian clock does not keep perfect time on its own, relying on environmental light stimulus to coordinate biologic activity. In mammals, this process is controlled predominantly by the Suprachiasmatic Nucleus (SCN), which is located in the hypothalamus and also drives peripheral clocks throughout the body.
Perception of light occurs through photoreceptor cells located in the retina that communicate directly with the brain—these include rods, cones and intrinsically photosensitive retinal ganglion cells (ipRGCs). Rods and cones are responsible for visual image forming, while ipRGCs modulate non-visual responses to light, most importantly circadian entrainment2. What is unique about ipRGCs is the presence of a photopigment known as Melanopsin, which is particularly sensitive to blue light in the range of 440–480 nm3. Melanopsin has also been found to be present in the skin and subcutaneous fat, which means skin exposure to blue light matters as well.
When Melanopsin becomes excited by the presence of short wavelength blue light, the message is passed to the SCN which stimulates a cascade of physiologic action. One of the most important actions resulting from this process is the synthesis and suppression of melatonin2.
Melatonin is found almost universally in all living organisms. As a hormone, its primary goal is to affect action throughout the body. Although most commonly associated with sleep/wake, the story goes far deeper. In fact, melatonin is a powerful antioxidant responsible for critical mitochondrial function and protection, cell death and repair, metabolic processes, immune system modulation and much more. As such, melatonin levels are one of the most critical aspects of avoiding disease and creating optimal health4.
Melatonin synthesis occurs in the pineal gland and is modulated by cues from the light environment received by Melanopsin and projected to the SCN. In the morning, the presence of visible blue light suppresses Melatonin synthesis and increases production of cortisol, serotonin, and dopamine—this helps you feel alert and energized. As the day progresses and the sun’s spectrum becomes absent of blue, melatonin synthesis and secretion is stimulated—this allows for quality sleep and cellular repair. Peak levels of melatonin occur around the middle of the night, after several hours of total darkness. Levels again begin to fall as it becomes time to wake up and the process repeats, creating a predictable, efficient rhythm of physiologic function5. But, what happens when blue light is present all day?
Enter Artificial Blue Light
Use of artificial light has become nearly ubiquitous throughout our lives. There are two sides to the story of non-native, artificial light as it relates to circadian alignment—chronic disruption and the promotion of an indoor existence.
First, modern lighting and technology peaks in the blue range, unbalanced by the remainder of the spectrum and unchanging as the sun would be naturally. Blue light has the greatest effect on circadian entrainment and constant exposure to artifical light signals daytime to the SCN, desynchronizing the circadian clock. While artificial light exposure is never good, use of it at night is the most disruptive to the circadian mechanism, resulting in the suppression of melatonin. The downstream effects are poor sleep quality, altered metabolism, inability to conduct cellular repair and growth and decreased cognitive function. For many, lifestyle choices make circadian misalignment a chronic state, resulting in chronic conditions6.
Additionally, the use of artificial light has enabled an indoor existence with 24/7 access to food, work, and leisure. For the majority of human evolution, the sun was the predominant source of light—when the sun was absent, the only options were to make a fire or go to sleep. Food was also tied directly to its photosynthetic origins and seasonality determined availability. However, proliferation of artificial light has enabled us to trade alignment with nature for convenience. Today, we no longer depend on the sun and instead spend our days and nights indoors, surrounded by artificial light with unlimited access to food7.
Chronic circadian disruption and an indoor lifestyle have serious consequences for health and aligns with the increase in modern day dysfunctions like:
What’s The Solution?
Mitigating and eliminating the presence of artificial blue, especially at night, is critical to optimal health. Here are some strategies for optimizing your light environment: