Sleep is a vital component of our health and body fat levels, yet many people long for a good night's sleep. A big factor behind achieving quality sleep is a stable circadian rhythm. One hundred years ago, it would have been nearly impossible to have a disrupted circadian rhythm simply because our light sources were restricted past sunset.
Today we stare at a brightly lit screen, held inches away from our face, well past sundown. Is our phone really affecting our health to such an extent that we're becoming fatter, sicker, and chronically fatigued? And if a small phone has such an effect on our health, what about the TV's and computer screens in every home? Could something as simple as blocking blue light solve an obesity crisis?
Humans need sleep. We die if we don’t sleep for 10 days. Studies have shown that a third of American adults are chronically sleep deprived (1). Lack of sleep negatively affects memory, creativity, the immune system, muscle repair, inflammation, hormone levels, and even our body fat levels.
Lack of sleep (or lack of quality sleep) is linked to higher fat levels, obesity, and higher cortisol hormones. Excess cortisol often leads to accumulation of excessive belly fat. However, it's not simply poor sleep that is the cause of fat gain; hormonal disruption also plays a huge role.
A lot of us have trouble falling asleep or have poor, interrupted sleep, leaving us feeling drained in the morning.
If you are a poor sleeper, you’ve probably tried all sorts of methods such as herbal teas, meditation, or sleep supplements. Unfortunately, some people even rely on drugs to achieve their nightly state of Zen.
This shouldn’t be the case. Our bodies desire sleep.
So what’s causing all these sleep issues? Is it the high amounts of caffeine? Or the stress of work that keeping us up all night? These could both be factors, but there’s something bigger than stimulants or stress. It plays a vital role in our lives, regulating far more than just our sleep. In fact, it affects every cell in our body, our immune system, our mood, and our hormones. What holds such power?
When one thinks of light, they generally imagine the visible light which allows us to see. When we switch a light bulb on, this produces light (and other forms of energy such as heat). But there is a lot more to light than the colours of the rainbow. Visible light is only a small part of the electromagnetic spectrum.
This spectrum is a range of frequencies or varying wavelengths of energy. Visible light makes up a very small part of the electromagnetic spectrum
There is a lot more to light than meets the eye, or should I say, appears to meet the eye.
For the purposes of this article, we are going to focus on the visible light spectrum ranging from about 390nm to 700nm. With changing wavelengths we see different colours. Pretty, sure, but these varying wavelengths cause different effects on the body.
How does light affect mood, hormones, and more importantly, sleep? It’s all about your circadian rhythm.
The term circadian rhythm comes from the Latin words circa (meaning approximately) and diem (day). The most obvious circadian rhythm is the sleep-wake cycle, though other circadian rhythms exist such as rhythms in body temperature, hormones release, and even gene expression (2).
Everyone has slightly different circadian rhythms, but on average, the length is 24 and a quarter hours (3). Night owls will have slightly longer circadian rhythms, while early birds have shorter ones.
Source - http://cdn.zmescience.com/
As mentioned before, circadian rhythms do more than simply tell the body when to be asleep or awake; they also influence the hormones released in the body.
Hormones are powerful things. If your circadian rhythm is out of whack your body could be releasing cortisol late at night instead of first thing in your morning, which would leave you feeling groggy in the morning and wide-awake late at night. Sound familiar?
So how do the body and circadian rhythm keep track of time? The same way humans do - by using clocks! Scientists have found that nearly every cell in the body keeps track of time.
Venice Greenwood from Quanta Magazine explains it like this:
“Every 24 hours, responding to a biochemical bugle call, a handful of proteins assembles in the cell’s nucleus. When they bind to each other on the genome, they become a team of unrivaled impact: Under their influence, thousands of genes are transcribed into proteins. The gears of the cell jolt into motion, the tissue comes alive, and on the level of the organism, you open your eyes and feel a little hungry for breakfast.”
These cell clocks, appropriately known as circadian clocks work by responding to light and darkness cues from the suprachiasmatic nucleus located in the hypothalamus. Functions that are regularly carried about in the body can be traced back to the cell’s circadian clocks.
Hair cells, for example, divide at a particular time every evening. The liver releases enzymes to assist digestion at meal time (which is why I recommend eating at consistent times every day), and the body prepares for sleep in the evening - that is, assuming these clocks are working properly!
Now that we understand how our body keeps track of time, it’s easier to understand how the circadian rhythm impacts our hormones, how we feel and how we perform. The body likes and expects routine. Can you see now why you feel so horrible after travelling across multiple time zones?
The body runs on cycles. Some functions happen at night, others during the day. When one is healthy, the clocks are in sync and the body's activities properly coordinated.
A disruption of this coordination not only leads to a feeling of perpetual jet lagged, but also:
Along with these health issues, misfiring circadian rhythms are linked to memory and learning inhibition (4). This is why resetting your circadian rhythm can be the most effective way of improving not only your sleep but also your health.
Most of us have experienced how long haul flights can disrupt our circadian rhythm, but there is a multitude of other factors that can mess with our circadian rhythm. A study published earlier this month in Science Translational Medicine found that “caffeine at night delays the human circadian clock” (5).
Researchers found that 200mg of caffeine (equivalent to a double espresso) 3 hours before bedtime created a 40minute phase delay in the test subjects’ biological clocks. They showed that caffeine had a direct effect on the internal clocks in human cells.
Drinking coffee at night affects sleep. No surprises there. This same study, however, had an interesting finding that was overlooked by the media.
The researchers not only tested how caffeine affected circadian rhythm, but they also looked at the light. The outcome – bright light delays one’s circadian rhythm more than of a double espresso does. A lot more, in fact.
Stone Hearth Newsletters reported the following on these findings:
"Bright light alone [...] induced circadian phase delays in the test subjects of about 85 minutes.” Double that of the caffeine-drinking group.
Yes, you read that right. Bright light delayed the circadian rhythm by twice as long as a double espresso.
Our body is constantly receiving signals from our environment. One of the most important, yet often overlooked, signals is that of light or the lack thereof. If we go back to the year 1878, before Thomas Edison had invented the light bulb, our light sources were limited to fire (candles) and the moon once the sun went down.
There were no TVs, no smart phones, no digital alarm clocks, and not even a blinking LED from a smoke detector! The body’s exposure to light past sundown was extremely low.
If we think about the hundreds of thousands of years of human evolution and adaptation to our environment, 150 years is nothing. Our bodies lived in light and dark cycles. When it was dark, we were restricted to low-light activities such as reading, writing, talking, having sex, and obviously, sleeping. When the sun was up we fished, hunted, made shelters, played, and worked.
Our bodies and circadian rhythm evolved based on this light-dark cycle. Today, 138 years after the invention of the light bulb, our bodies are still programmed to function in this light-dark cycle.
For example, it has been shown that morning exposure to bright sunlight helps reset our circadian rhythm, especially if it has been disrupted (6). If you travel, you should get morning sun light exposure when you arrive at your destination, or if you are a night owl with poor sleep habits, morning sunlight exposure will help address your sleep issues. You can learn more about this in my article, "How to Improve Sleep With Morning Sunlight."
Along with morning sun exposure, you should also expose yourself to sunlight during the day, although the best time is definitely the morning. Jack Kruse understands this topic better than anyone I know. I highly recommend reading his work for more on morning sunlight.
If you’re thinking that instead of going outside every morning you’ll just turn the lights on in your room, I need to point something out: it’s not the same. It’s all about lux. Lux is a measure of light brightness as seen by the human eye.
For comparison purposes, moonlight is about 1 lux. A brightly lit office is about 400 lux. An overcast day is about 2,000 lux. A spring day is about 40,000 - 60,000 lux. Bright summer sunlight is about 120,000 lux! (7). Can you see why getting outside is so important? Not to mention the beneficial effects of UV exposure on the skin.
You can actually test this for yourself. Download a lux meter on your phone and take some readings. I don’t know how accurate these apps are, but it should provide some insight into brightness levels.
Finally, I need to point out that the body senses light not only through the eyes but through the skin as well (2). In fact, vitamin D is synthesized in the liver and kidneys through the skin’s exposure to UV-B light. So when you’re outside, be sure to expose as much skin as possible.
Takeaway: Morning sun exposure is vital for optimal circadian rhythm functioning. If you work indoors, aim to go outside for brief spells during the day.
Light itself is the most important factor in setting our circadian rhythm. There are different colours in the visible light spectrum, and different colours have different wavelengths. Different wavelengths of energy cause different biological effects on our body. For example, it has been shown that a specific wavelength of red light can regrow tooth dentine and infrared saunas have been shown to have health beneficial detoxifying effects.
When it comes to looking at the wavelength of light which impacts circadian rhythms, studies have shown that blue and UV lights have the most impact. From an evolutionary perspective this makes perfect sense - blue light comes from the sun, with the highest levels of blue light reaching Earth around midday. As the sun starts to go down, the light becomes orange and red in colour. If you have watched a sunset (or even a sun rise), you have noticed how the colour was very red when compared to a white midday sun.
If we travel back to the 1800s again, the only time we were exposed to blue light (or UV light) would have been during the day. Come sundown, light sources would have been restricted to candles and fire. If you look at the image below, you can see how the candle puts out primarily orange and red light with very little blue and UV wavelength light.
Source - http://spie.org/
Understanding the difference between light colours is important if you want to optimize your circadian rhythm, sleep, and health.
I should also point out that when I talk about blue light it doesn’t have to be solely blue light. White light (from a fluorescent bulb or midday sun for example) is comprised of blue light.
The following image does a great job of showing the colour frequencies that make up various light sources:
You will notice how modern LED and fluorescent light bulbs actually put out a lot more blue and green light than a traditional candle or even an incandescent light bulb.
Takeaway: Sunlight, which is up to 100 times more powerful than room light in the blue and UV spectrum, is the best type of light for setting circadian rhythms.
What is the connection between light, circadian rhythm, and sleep? The answer is melatonin.
Melatonin is a hormone secreted by the pineal gland in response to darkness. It is commonly referred to as "the sleep hormone," but it also plays a vital role in controlling inflammation levels in our body while aiding our immune system (this is why, if you have a few nights of insufficient sleep, you’ll often catch a bug or become run down). It achieves this through its antioxidant properties. When people ask me what antioxidant supplements they should take I tell them to save their money and get their sleep back on track first.
Melatonin is generated after about 4 hours of darkness (the kind where you can’t see your hand in front of your face ) and generally peaks around 2am.
It runs opposite to cortisol: when melatonin is high, cortisol is low in this state, you should be sleepy. When melatonin is low, cortisol is high, you should feel alert and energized for the day. A good picture of this relationship can be seen here:
Source - http://en.licht.de
Melatonin is also the link between sleep and fat loss, as melatonin causes leptin to be released during sleep. Leptin (the hormone that causes you to feel full after a meal) enters the hypothalamus, your thyroid is up-regulated, your metabolism increases, growth hormone is released, and the body burns fat.
Circadian dysfunction is linked to obesity and it appears that leptin is the key. Researchers are finding that circadian clock deficiency or chronic jet lag leads to leptin resistance, and leptin resistance creates hormonal irregularity and fat gain. This is the body fat that, no matter how hard you train or how strict your diet, just won't go away. Hormonal cycles are crucial not only for sleep but for maintaining a healthy weight.
As we outlined above, light, and blue light in particular affects our circadian rhythm. Light influences melatonin secretion, with blue light having a far greater impact than red light.
The Harvard Health Publication sums it up nicely: "While light of any kind can suppress the secretion of melatonin, blue light does so more powerfully. Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to exposure to green light of comparable brightness. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours)" ("Blue Light Has a Dark Side").
Modern technology is the worst source of blue light in today’s environment. A study appearing in The Proceedings of the National Academy of Sciences titled, “Evening use of light-emitting eReaders Negatively Affects Sleep, Circadian Timing And Next Morning Alertness” found that "The use of light-emitting electronic devices [...] before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses [...] melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning" (8).
This study on fruit flies found that a single pulse of light to the brain was enough to disrupt circadian rhythm by 2 hours!
If you’re still not convinced that artificial light at night can impact circadian rhythm, melatonin secretion, and sleep, then here are a few more studies to prove my point:
A paper in The Journal of Clinical Endocrinology & Metabolism titled “Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans” found that, "Compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min. Also, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50% in most (85%) trials" (9).
In another study, dim light exposure at night was shown to disrupt circadian rhythms and lead to an increase in bodyweight (10). The study used a light source emitting 5 luxes of light. Remember, moonlight is about 1 lux. So that green charging light glowing on your bedside table could be impacting your sleep.
Finally, if you have light-coloured eyes you need to be even more careful about night time light, as it has been shown that your eye colour can affect melatonin secretion (11). Researchers found that people with light-coloured eyes are more sensitive to melatonin light suppression than those with darker eyes.
So which sources of artificial light emit blue light? Let’s look again at that chart from earlier:
We can see that modern LED and fluorescent lights contain high amounts of blue light. The researchers who created this chart also tested how each light sources affected melatonin, and found that high levels of blue light had the greatest effect on melatonin suppression. Brightness was also a determining factor.
There’s an excellent site called fluxometer that shows you the light output of various devices, ranging from the iPhone to streetlights. I recommend heading over there and playing around. It will also show how bright the light from a device is compared to daylight, and the resulting circadian rhythm phase shift. Here's a screenshot from the iPhone 6 report.
Takeaway: Light exposure at night shuts down melatonin production with blue light having a huge impact compared to red light. Blue light sources include modern light bulbs, computer screens, cell phones, and TVs.
From an evolutionary perspective, blue light impacting melatonin makes perfect sense. Prior to 1878 the only time we were exposed to blue light would have been during the day. We are diurnal (daytime) creatures, programmed to be outdoors when the sun is shining and home in bed when it is not. Nighttime = darkness, and darkness = sleep.
However, we don’t live in the 1800s. Light is available 24 hours a day. We all carry light-emitting devices such as the phones in our pockets. If it’s the middle of winter and the days are short, we play God and turn on energy-efficient ultra-white light bulbs, which give off more blue light than older incandescent bulbs. We then watch TV or work at our LED backlit laptops with screens that emit more white light than older technology displays.
If that’s not enough of a light assault on our body, we get into bed and hold a screen inches from our face. The icing on the cake is the blue LED blinking right next to us as our array of devices charges while light from the LED streetlamp outside seeps in through the curtains! Jack Kruse sums it up nicely:
“Every time we look at our phone, we send a signal to the brain that the sun is up.”
If you think all of this is crazy, take a look at astronauts who become susceptible to a wide range of diseases due to being in space. When in orbit, astronauts experience 19 sunrises and sunsets in a 24-hour period. This is what happens when you take something out of the environment it was designed to live in.
People understand this in the context of space and illness, yet every night here on planet Earth, we flash signals to the brain that the sun is rising. We then blame our health and sleep woes on uncomfortable mattresses or a stressful day.
The solution to improving our sleep is simple: eliminate artificial light at night. A 2013 study even found that one week of camping with no artificial lights (not even flashlights), synchronized the circadian clocks of the eight study subjects with the timing of sunrise and sunset (12).
So let’s summarize what we have learnt so far. We know that:
How can you achieve all of this? One option is to escape from the grid and move into the bush without any electricity. That would work.
But for those of us who enjoy the world we live in with all its marvellous technology, we can still control the kind of light we expose ourselves to.
You can probably guess how. In a nutshell, it involves:
Who would have thought? Expose yourself to the sun when the sun is up and avoid light (artificial light) when the sun is down!
Let’s look at some practical steps to help us make this a reality.
Every time we move away from our natural environment, we disrupt our body’s cycles and therefore our health. Light has a massive impact on both of these things yet many are blind to its power, especially when it comes to sleep. Artificial light has changed dramatically over the past 150 years and more so over the past 10-15 years, with the popularity of white light energy efficient bulbs and screens. Today we are flooded with artificial blue light 24/7.
This 'new light' is not only disrupting natural hormone cycles, but it's causing leptin resistance, obesity, and health issues. Artificial light at night is making us fat.
Though the ideal solution would be living a ‘caveman’ lifestyle, this is impractical for most. Fortunately, there are solutions and workarounds that enable us to live in a modern, technology-based society without disrupting our circadian rhythm.
Cut screen time in the hours prior to bed, use candles for light after sundown, and wear blue-blocking glasses when you must use a screen. If you're really struggling with your sleep, be sure to check out my Sound Asleep Program that covers everything you need to optimise your sleep quality.
There we go: a simple candle really can make you lose weight and bring back high-quality sleep!
How does light impact your sleep? Do you read articles on your phone while in bed? Maybe you're reading this article on a bright screen at night right now! Would you consider reading books by candle light?
2. Castro, R, Angus, DC & Rosengart, MR. The effect of light on critical illness. Crit Care (2011). at http://www.biomedcentral.com/
4. Fernandez, F, Lu, D, Ha, P, Costacurta, P & Chavez, R. Dysrhythmia in the suprachiasmatic nucleus inhibits memory processing. Science (2014). at http://www.sciencemag.org/
5. Burke, T. M. et al. Effects of caffeine on the human circadian clock in vivo and in vitro. Sci Transl Med 7, 305ra146 (2015).
6. Bechtold, DA, Gibbs, JE & Loudon, A. Circadian dysfunction in disease. Trends in pharmacological sciences (2010). at http://www.sciencedirect.com/
7. Theories of Light: From Descartes to Newton.
8. Chang, A.-M. M., Aeschbach, D., Duffy, J. F. & Czeisler, C. A. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc. Natl. Acad. Sci. U.S.A. 112, 1232–7 (2015).
9. Gooley, J. J. et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J. Clin. Endocrinol. Metab. 96, E463–72 (2011).
10. Fonken, LK & Aubrecht, TG. Dim light at night disrupts molecular circadian rhythms and increases body weight. Journal of biological … (2013). at http://jbr.sagepub.com/
11. Higuchi, S, Motohashi, Y & Ishibashi, K. Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light. American Journal of … (2007). doi:10.1152/ajpregu.00355.2006
12. Wright, KP, McHill, AW, Birks, BR & Griffin, BR. Entrainment of the human circadian clock to the natural light-dark cycle. (2013).
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