It is from the invention of the light bulb that we no longer depend on the natural light of the Sun for our main activities.
Today, more than ever, many people spend a large part of the day not only in artificially lit rooms, but also in front of a display (smartphone, PC, TV). Recently, there are several studies expressing concerns that looking at bright screens in the evening can upset our circadian rhythm, the internal clock that regulates our sleep-wake cycle.
This means that watching a display before bed makes it harder to fall asleep.
There are many products that filter out blue light on displays, promising to improve the quality of the sonno. Do they really work?
Is it really that simple? If screen light changes our circadian rhythm, just filter it to solve the problem? Things are more complicated than that.
How does the circadian rhythm work?
The circadian rhythm is an innate "biological clock" found in many forms of life, including plants, fungi and animals. In humans, the biological clock is found in the hypothalamus.
The hypothalamus releases a hormone called melatonin. Melatonin is often referred to as the "sleep hormone" as its levels are high at night but drop just before waking up in the morning. The watch has an inherent rhythm, but it can also be adjusted in response to light.
Is technology changing our circadian rhythm?
Professor John Axelsson, sleep research expert at the Karolinska Institute, explains: “Our internal clock follows an intrinsic circadian rhythm of nearly 24 hours. It is very sensitive to light around dusk and dawn, and this allows our systems to be dynamic and adapt to seasonal changes in the length of day and night. "
Many aspects of modern technology, from the basic light bulb to the brand new touchscreen phone, emit light. Professor Jamie Zeitzer of Stanford University says: “Light does two things mainly to the clock. Set the clock time and change the amplitude or strength of the clock ”.
As our circadian rhythm changes melatonin levels, we can look at the levels of this "sleep hormone" to see what is upsetting our biological clock.
And what we see is not clear. Several studies have shown that intense and artificial light suppresses the production of melatonin in humans.
Good light and bad light for the circadian rhythm
Interestingly, very bright artificial light is actually used for phototherapy as well, which helps people with a lot out of biological clock to wake up and fall asleep earlier.
The intensity of the light used for phototherapy is much higher than that emitted by any screens or light bulbs we use.
A study (from 2014) looked at a more realistic scenario: comparing melatonin levels and sleep quality of people who read a regular book or ebook before bed. They found that the participants with the ebook had reduced melatonin levels.
Doctor Cele Richardson of Western Australia University says, "There is evidence that 1,5 hours (or more) of display use reduces the natural nighttime rise in melatonin, and this effect is aggravated over multiple nights."
It is important to point out that "however, this does not seem to translate into a time required to fall asleep".
What does this mean for our sleep patterns?
Although we know that melatonin has many effects on the body and is associated with the circadian rhythm, we don't know exactly how and how much reduced melatonin affects our sleep quality.
There are many studies looking at the use of technology and the quality of sleep or the time it takes to fall asleep. Many of these find a correlation between screen time and sleep, but these are weak correlations. They don't show that increasing screen time causes sleep problems.
The 2014 study I cited found that on average paper book readers fell asleep 10 minutes earlier than ebook readers. Other studies have compared people who use display filters to regular users. Here the difference noted is only 3-4 minutes in the time it takes to fall asleep.
So many variables
Since sleep is affected by many factors, it is often difficult to make sure that it is just the effect of time spent in front of a display.
A two-way relationship between technology and sleep is also likely. Yes, the use of technology can affect sleep over time, but technology can also be the effect of sleep problems. People who have trouble sleeping can later increase their use of technology.
A summary, at the moment, is lapidary:
technology, especially that involving artificial light, changes our circadian rhythm.
We know this because there are definitely differences in melatonin levels after using the display.