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, our 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 we 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 Figeuiro 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.
Prof. Figueiro said:
"Our study shows that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent. 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
Figueiro said "Based on these results, display manufacturers can use our model to determine how their products could affect circadian system regulation."
The team says their 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. (SAD treatment involves sitting in front of a light box each day for one or two hours).
Melatonin is a "the hormone of darkness"Melatonin, or N-acetyl-5-methoxytryptamine is a hormone, also an antioxidant, which occurs naturally in all animals, plants and microbes. In animals (this includes 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.
In humans and other mammals melatonin is secreted by the pineal gland.
Melatonin is secreted when it is dark, that is why it is sometimes called the "hormone of darkness". Our highest melatonin levels usually occur during bedtime.
Technology is robbing us of natural darknessPrehistoric 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.
Co-author, Brittany Wood, said:
"Technology developments have led to bigger and brighter televisions, computer screens, and cell phones. 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 group - they 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 group - The tinted glass can filter out short-wavelength radiation which suppresses melatonin. This was the "dark control" condition.
- No goggles group - they wore no glasses or goggles. Their tablets were set to maximum brightness.
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, and considerable after 120 minutes.
Prof Figuiero said:
"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."