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Late Night Blues

This is the first in a series of articles I wrote for my final year portfolio. It is about the effects on sleep cycles of using phones late at night, and is aimed at the scientifically literate general public.

Date : 05/05/2017

Author Information

William

Uploaded by : William
Uploaded on : 05/05/2017
Subject : Medicine

Late Night Blues could your phone be keeping you up?

We ve all done it. Its midnight, and you have to wake up early in the morning. You re just drifting off to sleep and your phone buzzes. You re awake again, the light from the screen casting a blue light over your tired eyes. Once you ve turned it off, you feel restless, and in the morning are tired after a poor night s sleep.

Sleep, Light and the Brain

But why was it so hard to fall back asleep? In order to find out, we must explore how sleep occurs in the first place.
The retina is a sheet of cells at the back of the eye that is responsible for receiving light. It translates light into electrical impulses that transmit signals in the form of action potentials to the brain along the optic nerve. At the rear of the retina are the cells that receive light, then in front of them the wiring that links the retina to the optic nerve.
There are several kinds of light- sensitive retinal cell, called photoreceptors, in humans. Rod and cone cells are used to see objects rods handle dim light conditions, and cones bright light and colours. There is a third class of cell, however, which has only recently been discovered. These were named Intrinsically Photoreceptive Retinal Ganglion cells (ipRGCs). All of these cells possess light sensitive proteins called opsins in their membranes which are used to translate light into changes in membrane potential.
These cells are different in structure to the ordinary photoreceptors. Unlike the other cells, which are all at the back of the retina, they are found further towards the front of the retina, in the ganglion cell layer. In actual fact, they are modified nerve cells, which led to their name. The opsin they express is named melanopsin, and is most sensitive to blue light of 480 nanometres in wavelength (this will become important later). All of the functions of ipRGCs are not clear, however the most important to us is that they are involved in telling the brain what time it is based on the light environment. When blue light strikes them, action potentials are sent along the optic nerve into the brain.
Signals from the retina - and in particular, ipRGCs, travel up the optic nerve. They end up in an area of the brain which is responsible for timing - the suprachiasmatic nucleus (SCN). This input tells the brain what time it is outside , and establishes the rhythm of days and nights, and causes activity to change. This activity is higher during the day and lower at night. The change is reflected at the genetic level. Genes known as clock genes switch their activity on and off according to a regular pattern, and so allow the whole area to tick like a clock . The interactions of all these genes produce a rhythm of around 24 -26 hours, and so give our bodies a biological interpretation of the time of day by allowing brain activity of the area to decrease at night and increase as we wake up in the morning.

The Rhythm of Life

These rhythms are known as circadian rhythms, from the Latin circa (about) and diem(day). Critical for the survival of most organisms, they allow the body to react appropriately to different conditions during day and night. Circadian rhythms affect many different aspects of human biology however one of the most critical is our sleep cycle.
Given that it is dark at night and light in the day, information from the retina will affect this rhythm. When action potentials arrive at the brain, the pattern of activity changes so that the timing of circadian rhythms keeps pace with the different light conditions - information about what time it is literally re-sets the clock every morning. This is important, as it allows us to keep our biological rhythms appropriate to the time of day.
For example, jet lag: when it is half past in the afternoon in London, it is half past ten in the morning in New York. If you fly from London to New York, you would initially feel sleepy at about 6pm because in London it is approaching 11 at night. However, you adapt to the new cycle of days and nights, and after a few days, you adapt and soon you feel no different in New York than in London.
The last stop on the pathway to sleep is the hormone melatonin, a supremely important molecule in making one feel sleepy. It was discovered largely by accident in 1958 by the scientist Aaron Lerner, who observed that it lightened skin colour in frogs and so hoped to find a cure for an unpleasant (if harmless) condition known as vitiligo where the skin develops dark patches. He didn`t cure vitiligo, but he did observe that injecting melatonin made him sleepy. More than 50 years later, we have uncovered a significant role for melatonin in sleep - its concentration peaks at around 3:00 am, corresponding to our deepest sleep, and suppressing melatonin release with drugs causes sleep to happen later. Scientists are unsure whether melatonin simply puts the brain to sleep, like an anaesthetic, or have a more complicated role however it is important and so can be measured to give us an idea of the state of sleep.

Is There a Problem?

It s been known for some time that sleep quality has been declining in the general population, but especially in young people. The average sleep time in the 1950 s was eight and a half hours in 2011, it was six and a half. Most people between the ages of 16 and 25 now go to sleep late at night, and rise early in order to get to school or university, and then attempt to make up the lack of sleep by lying in on weekends and days off. At the same time, most young people own at least one electronic device - in one study, 97% of American teenagers reported that they kept some sort of phone or computer in the bedroom. This increase in ownership has seen a subsequent increase in social media use, with 8 out of 10 people under the age of 20 using social media regularly. It may not come as a surprise, then, that these two phenomena appear to be linked. Over the last ten years, the case for electronics disturbing sleep has been growing late night TV has been associated with poorer sleep and daytime feelings of tiredness likewise computer, smartphone and social media use. But what about electronic media causes this?

The answer may lie in the blue light that is emitted by the screen. Most smartphones and computer screens emit large quantities of blue light in the 450 - 80 nanometres range. This happens to fall within the receptive range of those specialised retina cells that assist in setting circadian rhythms. Therefore, we have a tempting theory to test - is blue light from the screens of mobile devices stimulating the part of the retina that tells us when it is appropriate to fall asleep?
This is where melatonin comes in. As we discussed, this molecule reflects the sleep state of the organism it is released in. Therefore, we should expect to see some sort of change in melatonin levels if the light from screens affects sleep. And so we do - exposure to a backlit screen for just 2 hours will push melatonin down by 22%, a similar decrease to that which happens in daylight. However, the time one is exposed is significant using the screen for only one hour had no effect.
Another study went a step further - the scientists here gave 3 groups of people different sets of goggles orange-tinted lenses which blocked out blue light, blue tinted lenses which allowed blue light through, and clear lenses that had no effect. The test subjects were then asked to use tablets for various lengths of time, with varying brightness on their screen. The findings of this study were very similar to the first using a screen for two hours had an effect on the patient`s melatonin concentration, but decreasing the time exposed reduced the impact. Interestingly, the blue tinted goggles were significantly more damaging to melatonin levels that both the orange and clear lenses - this points to blue light as a culprit in damaged sleep.

This is all very well, but one might argue that it was the fact that we are concentrating on something interesting that causes us to stay awake. After all, most people using social media are at least vaguely aware and interested in what is happening, and so may be kept awake simply by higher overall brain activity suppressing feelings of tiredness. This mode of sleep - suppression was tested in by scientists who made a group of teenagers play violent, exciting computer games ( like Call of Duty) at night, and compared their heart rates and sleep length to a group who played a more sedate game like Tetris. The group who played the more exciting game suffered both poorer and shorter sleep, even when the screens were adjusted to emit less blue light. However, these findings were contradicted by yet another team, who observed that people who read a book - something that clearly does not emit blue light - slept longer and felt more refreshed than those who read an e-reader. Both groups were concentrating, so the team concluded that the light being emitted must have caused the problems e-book users had experienced.

Beat the Blues

So what can we conclude from all these studies? Clearly one of the causes of our sleep problems are linked to our use of electronic devices and using them late at night is undoubtedly a bad idea. There appears to be a link between the light emitted and how we sleep, but because of the difficulty of studying humans, it is tricky to say for sure whether this alone or a combination of factors, that stops us sleeping well.
But we can come up with some practical solutions to technological insomnia. First of all, using something with a bright screen in the hour or so before sleeping is inadvisable - either the light will wake you up, or the act of using a device at all will. It also helps to get more sleep - the simplest way to solve a lack of sleep is, after all, to get more by going to bed earlier. However, if you can t let go of your online life, it may be possible to dodge the worst side effects of light exposure. Turning the brightness down can help, but better are apps such as Bluelight or f.Lux reduce the proportion of blue light and increases the orange and yellow balance, making late night browsing safer and more pleasant. So if science is right about the link to blue light, we might not have to ditch the late night texting after all.

Further Reading:

Circadian Rhythms: https://www.sciencedaily.com/terms/circadian_rhythm.htm

Light Exposure at Night: https://www.newscientist.com/article/mg21028111-400-blue-alert-the-dark-side-of-night-light/

This resource was uploaded by: William