“In lieu of what we know about how profoundly light can affect our brain and overall health, every time we light up a room, step outside to daylight, draw the curtain, or put our sunglasses on, we are sending either good or bad signal to our brain. Light truly is as powerful as any drug in its potential to affect our brain and overall health. If light is a drug, then we must figure out how much light and what kind of light (i.e., what color) should be consumed when to promote mental health and general well-being.” - Dr. Satchin Panda
Modern humans spend unprecedented amounts of time indoors. In this series, I argue that our indoor lifestyle puts us at odds with essential nature-based inputs that can lead to poor health. One vital input our indoor lifestyle disconnects us from is natural cycles of light and dark.
In a consumerist wellness landscape, light is a highly underrated health ally. Light is so omniscient that it’s essentially like the air we breathe––vital and influential but easy to take for granted. Or more cynically, one might argue that light’s health benefits receive far less air time due to its lack of obvious commercial viability.
As a result of these factors, many people neglect to examine their relationship with light in their wellness protocol.
Our broken relationship with light illustrates the thesis of this series. First, it’s an example of the symbiotic co-evolution between humans and natural environments and how this connection is built into our biology. Second, the potency of sunlight vs artificial light shows us that there are benefits, related to both finances and efficacy, to accessing inputs directly from the natural world.
The scientific community hasn’t yet fully uncovered all the symbiotic benefits between humans and nature so accessing these inputs from the natural world is ideal. Sure, there are benefits to using blue light blocking glasses and light-boxes but these substitutes aren't likely to replicate the full potency of viewing daylight at the appropriate times and creating a dark environment at night.
Let’s dive in.
Human biology thrives on contrast. For example, we need both stressors and periods of recovery to become resilient. One well understood example of this comes from exercise science. A bout of exercise is a stressor on the body but when followed by adequate rest and recovery, the body is able to build itself back more strongly, conferring health benefits to the entire system.
The same principle of contrast applies to our relationship with light. We need robust signals of both light and darkness in order to thrive. Instead, modern environments lead to too little of both. We exist in “dim light” (akin to biological winter) most of the time rather than experience the appropriate contrast our bodies evolved to expect. We thrive with bright days and dark nights.
We evolved in close proximity to the natural world, which meant being exposed to predictable and alternating periods of light-dark every 24 hours. As diurnal mammals we are supposed to be active during the day and to rest during the night. Our body evolved to “tell time” from environmental signals.These environmental signals are known as zeitgebers––environmental inputs that serve as “time keepers.” The most robust signal our bodies read is light. Other zeitgebers include timing of meals and physical activity.
In order to read these zeitgebers our brain evolved with a “master clock”, also known as the suprachiasmatic nucleus (SCN). Photosensitive nerve cells in our optic nerve (Melanopsin ganglion cells) read light energy (photons) and send information about the lighting environment to the SCN which then sends signals to all our cells that help the rest of our body “tell time.” In addition to the “master clock” in our brain, we also have peripheral clocks. Our peripheral clock consists of clock genes present in nearly every cell of our bodies. Our peripheral clocks create their circadian rhythm from a combination of the light-induced SCN signal and meal timing.
Ideally, your master clock lines up with the peripheral clocks and both are in sync with light-dark signals in your environment. The body translates this environmental input into hormonal and neurochemical signals that help our body function optimally.
Syncing our circadian rhythm with the natural light-dark cycles in nature establishes a foundation for health.
Circadian misalignment is rampant. Indoor living and light-emitting devices cause us to be “out of sync” with the light/dark cycles of the sun. In this modern environment we rarely get a clear signal as to whether or not it is day or night. This circadian misalignment can manifest in a variety of ways. Common forms of circadian misalignment, such as shift work and jet lag, have been well-studied and linked to multiple negative health outcomes. So much so that the World Health Organization's International Agency for Research on Cancer classified shift work as a potential carcinogen. Circadian impairment has been linked to psychiatric disorders, gut alterations, sleep and cognitive impairments and various types of cancers. But even if you aren't a shift worker, most of us have chronically disrupted circadian rhythms. Researchers now have names for these mundane forms of circadian disruption: social jetlag and digital jetlag.
One of the cheapest, most potent wellness tools is to optimize your circadian system by improving your light hygiene. This optimizes foundational aspects of your biology. Circadian alignment (when our internal clocks match natural light-dark signals) evokes powerful, ancient systems that lead to health.
THE HAZARDS OF VIEWING LIGHT AT NIGHT
For most of history, as the sun set we were no longer exposed to bright light. We currently have an evolutionary mismatch from what our bodies have evolved to expect and the modern environment. With the invention of the lightbulb in 1879 and the digital revolution, we have unprecedented inputs of light at night leading to chronic circadian disruption.
One of the commonly known risks of light at night is that it suppresses the release of the hormone melatonin. Due to the popularity of melatonin as a supplement, melatonin is well known for its sleep-supportive benefits. Luckily for those of us who don't want to spend money on supplements our body produces its own melatonin, in the perfect form and dose, when given the appropriate light signals.
In dim and dark environments, melatonin––which has been called "the hormone of darkness"–– is released by the pineal gland as a circadian signal of nighttime and a sleep initiator. Bright light, particularly light in the blue spectrum, blocks our brains from producing melatonin. The use of artificial light and devices after dark abnormally suppresses melatonin which reduces both the quality of sleep and the ability to fall asleep. This is problematic for reasons beyond melatonin’s impact on sleep quality. In addition to its role in supporting our circadian rhythm and sleep, melatonin has several other biological benefits.
Beyond its influence on sleep, melatonin is also a potent anti-inflammatory, antioxidant, immunomodulating and cancer-protective hormone. Melatonin is highly conserved across multiple species and is even found in primitive photosynthetic bacteria. According to one paper I read, the original and primary function of melatonin is as a free radical scavenger and antioxidant. Another article I found in the prestigious science journal Nature called melatonin, “master regulator of inflammation and cell death.”
There is a lot of buzz about antioxidants. Antioxidant refers to any compound that can counteract damage caused by “free radicals”––molecules which are missing an electron, thus highly reactive––which generate oxidative stress, which can damage DNA, cells, and potentially play a role in aging. We generate free radicals as a normal part of metabolism and certain lifestyle factors can increase them. While there is a lot of hype about antioxidant supplements, the best data indicate that getting a range of antioxidants present in a diverse, plant-forward diet is most effective. A potentially underrated antioxidant source we evolved with is melatonin.
The ability of melatonin to reduce oxidative stress via its free radical scavenging actions is directly related to its concentration. At higher concentrations, there are more molecules of the antioxidant available to quench free radicals thereby lowering oxidative damage and related diseases.
Melatonin is also being studied for its anti-depressant qualities likely due to its ability to reduce neuroinflammation, depressive-like behaviors, and oxidative stress. Melatonin is a highly conserved biological resource that helps us deal with inflammation and oxidative stress. This paints a much more fascinating picture than a prosaic sleep supplement found in the aisles of CVS.
In summary, If we are deficit in darkness, we are deficient in melatonin. This means you're short changing your body of a powerfully reparative hormone we evolved to have a certain dose of every day. So, rather than investing in expensive antioxidant supplements (that likely don't work), prioritize your daily dose of darkness instead.
THE IMPORTANCE OF VIEWING BRIGHT LIGHT DURING THE DAY
In our sleep-procrastinating, screen addicted era, we've all likely heard of the hazards of too much blue light at night. But what has been underrated is the importance of outdoor daylight exposure during the day. People generally know that less light during the winter can lead to Seasonal Affective Disorder, which is a seasonal bout of depression. But the reality is that most of us, as far as our light environment is concerned, are living in permanent winter. This is the result of modern environmental influences that lead us to spend 90% of our time indoors––a dim lighting environment––and also getting bright light signals at unnatural times.
Just as darkness signals our body to prepare for sleep, appropriately timed light exposure during the day tells our body to be alert and active. It also locks in our circadian timing so we are less impacted by some of the harmful impacts of exposure to light at night.
If you work in a bright office or have good natural light in your home, it may feel like you are getting adequate light exposure indoors. Yet, indoor light is inadequate to confer biological changes because it simply is not bright enough to have an effect. For example, the brightest lit office spaces are generally only around 500 lux whereas being outside on a cloudy day exposes you to about 10,000 lux (up to 30,000 lux on a sunny day). Additionally, our eyes are most sensitive to light at night and least sensitive to light early in the day. Therefore, we need a higher dose of photons in the early part of the day to set our circadian rhythm. Because indoor lighting is so much dimmer than outdoor light, this simply means we have to get outside. As usual, the indoor solution is inadequate. If you want to test this for yourself you can download a lux meter on your phone.https://apps.apple.com/us/app/myluxrecorder/id106955783.
Cortisol, generally maligned as a stress hormone, is also a key signal for the circadian system. Cortisol is an "awakening and alerting" hormone that helps us feel energized during the day. Ideally, it follows a daily 24-hour curve with the lowest concentrations at night and a peak right before we wake up. Additionally, there should be a sharp peak in concentration within the first hour after waking, which is known as the cortisol awakening response (CAR). One signature of depression (and circadian misalignment) appears to be a blunted cortisol awakening response . One way to induce an optimal cortisol awakening response is to view sunlight in the morning. This sets you up for appropriate cortisol and melatonin rhythms. In addition to all the other circadian-related benefits, this is a free tool for optimizing mood and energy. No supplements needed.
Additionally, Samar Hatter, a circadian biologist at Johns Hopkins, did a study that linked exposure to light at night with both depression and learning problems. This is likely due to the activation of cortisol at inappropriate times, leading to cognitive impairment.
Another benefit of viewing lots of light during the day is that it strengthens your circadian entrainment. What this means is that you are less impacted by the bright you do view at night. Studies have shown that viewing adequate daylight during the day minimizes the melatonin blunting effects of blue light at night. This gives you a little more wiggle room in terms of how strict you are with your nighttime light routine.
You can use light boxes or other high tech solutions to engage with more light during the day but none are as elegantly designed for your physiology as simple sunlight. In the words of renowned light scientist Mariana Figueiro during her awesome Ted Talk on Light and Health, “Daylight is the ideal light source for the circadian system––it goes on and off at the right time, and is the right color and right intensity”.
*It’s important to mention that wearing sunglasses can reduce your bright light exposure by 7-15 fold, so don’t wear them on your walks where light exposure is the priority.
PRACTICAL TIPS
So, what are the top, low-cost behavioral strategies for translating this intriguing science to your daily routine?
My favorite heuristic for optimizing circadian biology comes from circadian biologist, Dr. Satchin Panda:
"Get as much daylight during the day, as little light as possible at night, and no light during sleep."
Practically speaking this means going outside more and having a more intentional relationship with technology.
Let's talk about strategies for implementing each part of the equation.
How to get as much daylight during the day as possible.
Prioritize getting outside in the morning. Aim to get outside in the morning for at least 5-10 minutes. This could mean taking a walk around the block or drinking your coffee outdoors.
Schedule at least 3 outdoor breaks during your day. This can be as simple as taking a 5-10 minute walk in the morning, at lunch, and right after work.
Don't wear sunglasses when you are outdoors (or blue light blocking eyewear). Wearing sunglasses blocks the light signal from reaching your brain.
Consider swapping indoor exercise for outdoor exercise. Find year-long outdoor hobbies. Depending on where you live, invest in the clothing and gear that allows you to engage with the outdoors even in harsh weather conditions.
How to limit light at night:
Use blue-light blocking technology as a harm-reduction strategy when you need to view light at night. F.lux is a great plug-in for computers and tablets that filters out the blue light as the sun goes down. Most smartphones have similar settings you can enable. Consider using blue light blocking glasses at night, although the spectrum of light may matter less than intensity so this isn’t a foolproof solution.
Invest in warmer-toned bulbs and dimmers. Turn on these lights at night and only use the minimum amount of lights needed after the sun goes down. Task lighting (non overhead lighting) is best. Bonus, this tends to create cozier vibes anyway.
Create a “digital curfew” –– a time at night, ideally 30-60 minutes before you plan on going to bed––where you stop engaging with screens. To be successful with this you’ll need to replace the screen-based nighttime habits with equally rewarding non-screen based activities. See next tip.
Find some non-screen based nighttime hobbies that help you unwind. For many of us this essentially means considering finding some high-quality alternatives to Netflix. For me, this is reading books with some groovy music in the background, yoga, or drawing while listening to audio books.
How to sleep in total darkness:
Get an eye mask. In the absence of any other interior design changes, this takes care of most of the light exposure during sleep. I always travel with an eye mask as it allows for higher quality sleep in new environments you don't have control over. To take it to the next level, install blackout curtains in your bedroom.
Get the TV out of your bedroom. At the very least, pick a time to turn off the TV at night (ideally 30-60 minutes before bed) and consider covering the TV up when you're not watching it. This helps break the associative loop of seeing a TV and wanting to watch TV.
Charge your electronic devices in another room. The most common retort to this is, "I use my phone as an alarm clock." My response is to recommend buying a non-phone alarm clock. This is a one time change that seems to determine success or failure with breaking the habit of looking at your phone right before bed and first thing in the morning.
Like many topics, there are a lot of high tech, expensive ways to optimize sleep, energy, and moods. I argue that none are as potent and effective as intelligently using light-dark cycles to optimize your circadian rhythm.
Light is an ally we co-evolved with. If we use the right spectrum and brightness at the right time, it positively benefits every system of the body.
The best part is that it is free and democratically available as long as you have access to the outdoors and commit to some simple rules around how you engage with technology.
CITATIONS:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4282293/ https://www.nature.com/articles/s41419-019-1556-7
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5503661/
https://www.frontiersin.org/articles/10.3389/fnmol.2020.00096/full
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.456.9753&rep=rep1&type=pdf#page=107
https://www.sciencedirect.com/science/article/pii/S155041310500269X
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.456.9753&rep=rep1&type=pdf#page=107
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4437603/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7068538/
https://www.sciencedirect.com/science/article/abs/pii/030645309290078L