SLEEP: Morning Sunlight & Mental Health

Most people know that they need to get enough sleep every night to promote overall health. In fact, “good sleep hygiene” has become a buzz word lately, namely referring to a list of good habits around sleeping, such as getting 8 hours of sleep, sleeping in a cool room, sleeping in total darkness, minimizing blue lights late at night, and avoiding caffeine past the afternoon. But did you know that there is another element that is critical to our sleep/wake cycles and overall health that is often left out of the good sleep hygiene equation? This is maintaining our circadian rhythm. In the simplest terms, our circadian rhythm is our body’s natural 24-hour cycle of sleep and wakefulness. But have you ever thought about how that actually happens?


It turns out that it is a very complicated series of chemical processes that happen on the cellular level in our body that control our ability to wake up in the morning and have energy throughout our day, as well as our ability to fall asleep and sleep deeply throughout the night. And it is all controlled by the SUN. As we evolved over millennia, our bodies needed a way to regulate this process. And we have special light-sensitive cells in the retinas of our eyes. They receive necessary information from the sun in the form of light waves to determine the time of day it is. As the sun is first rising in the sky in early morning, the wavelengths are a specific blend of blue, yellow, and red that our photic sensitive cells relay to the Suprachiasmatic Nucleus (SCN)— meaning our intrinsic “master clock” that sits in our hypothalamus in the brain. It is responsible for generating and synchronizing a host of bodily functions and rhythms, such as our peripheral organs, hormones, food intake, body temperature, motor activity, mood, memory, and other daily rhythms to an approximate 24-hour cycle. When our master clock gets this information from the cells in our eyes, it begins sending out a cascade of chemical signals to the rest of our body, such as for our adrenal glands to begin producing cortisol, which is what wakes us up and gives us energy to start our day, and also starting a timer in the pineal gland to begin producing melatonin later in the day, to help us wind down and fall asleep. The problem is that most of us don’t get the early morning sunlight we need to signal this bodily process, AND we get excess artificial light at night via our phones, tablets, and bright overhead lighting, etc. As the sun continues to rise in the sky, the blend of “colors” changes and no longer has the necessary yellow and red portions of the color spectrum that the receptors in our eyes are specifically designed to absorb in the early morning. So we miss this key window for regulating our circadian rhythm and delay our release of cortisol and subsequently melatonin gets produced later and later in the day. And as a society that constantly looks at primarily the blue waves of the light spectrum from all our electronics and fluorescent lights, we continue to signal to the brain that it is still mid-day (even at 11 pm). So we keep producing cortisol and suppressing the release of melatonin. It is an endless cycle. You might have heard of “blue-blockers” or specific glasses designed to be worn at night to block out the blue lights emitted from our devices. But that is only one part of the full equation. You need to expose your eyes to early morning sunlight for a minimum of 2 to 10 minutes every single day to regulate your circadian rhythm. And the more you do it, the more your body begins to expect this, and will even start proactively releasing the chemicals necessary for starting your day. You can literally shift your wake and sleep cycle to earlier in the day, even making night owls morning people. The earlier this process happens in the day, the earlier the melatonin production will begin in the evening. This is important for helping us prepare to rest and fall into a deep, restorative sleep. Any bright light at night (not just blue light) suppresses both melatonin production and dopamine. Dopamine plays a role in learning, memory, focus, and motivation, so damaged dopamine signaling at night creates addiction to screens and makes getting out of bed harder the following morning. It is also during our sleep that our brains are able to deal with experiences and emotions. And without proper deep sleep (which is often diminished due to excessive light exposure at night) we cannot fully process and integrate traumas and weaken the emotional ties to the memory of the event.


Decades of research has pointed to a connection between our phase of rhythms controlled by our master clock and mood. Several studies have shown that a disrupted circadian rhythm is connected to mood disorders, such as major depressive disorder, bipolar disorder, and seasonal affective disorder due to a delay or advance in hormonal rhythms. Since the SCN synchronizes many hormonal mechanisms, it can disrupt brain regions related to mood regulation. Current research states the necessity for people with mood disorders to seek early morning bright light to advance their timing and release of specific hormones in order to regulate their circadian clock and restore proper sleep.


Using blue blockers is a step in the right direction, as blue light can also lead to a condition called Digital Eye Strain and damage our mitochondria. BUT, they are NOT enough to protect against disruption of your sleep cycle if you are viewing bright lights at night in general. Indoor lighting has a very unnatural spectrum (heavy on the blue side) compared to that of natural light and it also never changes. This can wreak havoc on our body since we are essentially ruled by the continuously changing light frequencies from the sun to determine the exact time of day and what biological processes should be happening. The subsequent chaos leads to improper signaling of hormones and neurotransmitters, inflammation, and cellular dysfunction and damage. A good rule of thumb is to minimize all lights in the evening, especially bright lights, overhead lights, and blue lights. The orange and red end of the color spectrum emulates sunset and helps sync your body further to a 24-hour cycle. Candles, firelight, and specific red bulbs in lamps closer to the ground (since our eyes have evolved to most detect light from overhead—the sun) are the best types of light for nighttime. And always use blue blockers when using screens at night (or excessively during the day).


Author: Karen McKinney, LCMHCA



References:

  1. Jung, Christopher M., Khalsa, Sat Bir S., Scheer, Frank A. J. L., Cajochen, Christian, Lockley, Steven W., Czeisler, Charles, A., and Wright, Kenneth P. Acute Effects of Bright Light Exposure on Cortisol Levels. Journal of Biological Rhythms 25(3), (2010).

  2. Vadnie, Chelsea A. & McClung, Colleen A. Circadian Rhythm Disturbances in Mood Disorders: Insights into the Role of the Suprachiasmatic Nucleus. Neural Plasticity, (2017).

  3. Bedrosian, T. A., Nelson, R. J. Timing of Light Exposure Affects Mood and Brain Circuits. Translational Psychiatry 7 (2017).

  4. Hastings, Michael H., Maywood, Elizabeth S., Brancaccio, Marco. Generation of circadian rhythms in the suprachiasmatic nucleus. Nature 19, 453-469 (2018).

  5. Walker, W.H., Walton, J.C., DeVries, A.C. et al. Circadian rhythm disruption and mental health. TranslPsychiatry 10 (28), (2020).




Disclaimer: This information is generalized and intended for educational purposes only. Due to potential individual contraindications, please see your primary care provider before implementing any strategies in these posts.

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