Why Do Tablets Disrupt Sleeping Patterns?

By Christian Nordqvist, CEO, Medical News Today — September 03, 2012

Communication devices and tablet computers with self-luminous backlit displays can cause melatonin levels to drop, making it much harder to fall asleep, researchers at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, Troy, NY, explained. The authors of the report explained that if you have not yet gone to bed when exposed to a luminous screen for long enough, you will probably delay your bedtime.

Their study has been published in Applied Ergonomics and is titled "Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression."

Melatonin, a hormone, is involved in regulating our circadian rhythm or “body clock.” Fluctuations in melatonin levels influence on our desire to stay awake or go to sleep. During evolution, sunlight exposure determined what our melatonin levels were. Our bodies still respond to melatonin in the same way they did thousands of years ago. The difference today is that we now have other sources of light, which can upset our body clocks.

Studies have shown that disturbances in our circadian rhythm may lead to brain cell changes, and cause sleep problems in aging. Researchers at the University of Southern California found that circadian rhythm is much more important to life than had previously been suspected.

Research head, associate professor, Mariana Figuiero and team set out to determine what the effects of self-luminous tablets might be on melatonin suppression. They observed and gathered data on 13 volunteers who used the devices to watch films, play games and read documents.

"Our study shows that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent,” Figueiro says. “Stimulating the human circadian system to this level may affect sleep in those using the devices prior to bedtime."

Two-hour exposure to tablet computers before bedtime could be making us go to bed later. The melatonin suppression that occurred after exposure to the luminous tablet screen was similar to what one would expect after being exposed to normal sunlight, the researchers explained. In other words, the screen light makes the human's body clock regress from nighttime-sleepy to daytime-alert mode.

Figueiro says, "Based on these results, display manufacturers can use our model to determine how their products could affect circadian system regulation."

The team says the findings should be used to encourage gadget, tablet, mobile phone and screen manufacturers to create more circadian-friendly products which could follow our sleep-awake patterns, rather than work against them.

Perhaps manufacturers could design tablets to help people with certain conditions and illnesses linked to lack of sunlight exposure, such as seasonal affective disorder (SAD), and sleep problems commonly experienced by seniors.

Users could be receiving therapy for their condition while watching a movie, playing games, writing letters, or reading texts - much more fun that simply sitting in front of a light box, which SAD patients typically do each day for one or two hours.

Melatonin is a "The Hormone of Darkness"
Melatonin, or N-acetyl-5-methoxytryptamine, is a hormone and antioxidant which occurs naturally in all animals, plants and microbes. In animals, including humans, levels of melatonin fluctuate during the daily cycle. It is a "timing messenger" which regulates our waking and sleeping cycles. Doctors sometimes prescribe melatonin for people who find it hard to get to sleep.


Melatonin is secreted when it is dark, which is why it is sometimes called the "hormone of darkness." Our highest melatonin levels usually occur during bedtime.

Technology Robbing Us of Natural Darkness
Prehistoric humans, before they knew how to make fire, would go to sleep as soon as it was dark because their melatonin levels would shoot up after sunset. High melatonin levels make us want to go to sleep. After we knew how to make fire, we no longer lived in total darkness during the night. Then came candles, gaslights and the electric light bulb.

Technology today means that we can be exposed to intense light at any time of day and night.

"Technology developments have led to bigger and brighter televisions, computer screens and cell phones,” says co-author Brittany Wood. “To produce white light, these electronic devices must emit light at short wavelengths, which makes them potential sources for suppressing or delaying the onset of melatonin in the evening, reducing sleep duration and disrupting sleep. This is particularly worrisome in populations such as young adults and adolescents, who already tend to be night owls."

Wood and team divided the volunteers into three groups:

Clear goggles: Members of this group looked at their tablets through a pair of clear goggles. The goggles were fitted with 470-nm (blue) light from LEDs (light emitting diodes). Blue light is known to suppress melatonin. This was the "true positive condition."

Orange-tinted glasses: The tinted glass can filter out short-wavelength radiation which suppresses melatonin. This was the "dark control" condition.

No goggles: This group wore no glasses or goggles. Their tablets were set to maximum brightness.

Each participant wore a Dimesimeter near the eye. A Dimesimeter is a device that monitors and records circadian light and levels of activity. It was developed at the Lighting Research Center.

The team found that exposure duration and the distance from their eye to the tablet screen had a significant impact on melatonin levels. The impact on melatonin suppression was insignificant after 60 minute exposure, but was considerable after 120 minutes.

Figuiero says, "We recommended dimming these devices at night as much as possible in order to minimize melatonin suppression, and limiting the amount of time spent using these devices prior to bedtime."

*Mobile Enterprise Editor's note. This article originally appeared on www.medicalnewstoday.com here and is reposted with permission from the author. 

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