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 Plenty of previous research has linked reading on tiny screens to
disrupted or abbreviated sleep, especially when people use tablets
and smartphones right before bed.
But after 6.5 hours of constant bright light exposure during the
day, there were no differences in sleep between the 14 participants
in the current experiment, whether they read a traditional book or
on a tablet for two hours before bedtime.
“One plausible explanation for these discrepant results across
experiments, in our view, is that bright light exposure during
daytime – similar to that employed in the present study has
previously been shown to attenuate the suppressive properties of
evening light exposure on melatonin levels,” said lead study author
Frida Rangtell, a neuroscience researcher at Uppsala University in
Sweden.
Melatonin is a hormone that helps control the body’s sleep and wake
cycles, and bluish light emitted by tablets and other electronics is
thought to disrupt sleep by lowering melatonin levels.
“Our results could therefore suggest that light exposure during the
day, e.g. by means of outdoor activities or light interventions in
offices, may help combat sleep disturbances associated with (light
from electronic devices),” Rangtell said by email.
For the experiment, Rangtell and colleagues assessed participants’
sleepiness before bed and after waking up and measured
concentrations of melatonin in saliva each night.
Starting in the afternoons, participants were exposed for six and a
half hours to a constant level of light about equivalent to that
indoors next to the window on a sunny day.
Each person in the study started either by reading a book or a
tablet before bed, and then repeated the experiment a week later by
using the opposite format to read.
Researchers didn’t find any significant differences in sleep or
melatonin levels before bedtime between tablet and book reading, the
authors report in the journal Sleep Medicine.
The experiment may not have included enough participants, however,
to detect statistically meaningful differences between reading
tablets and books, the authors note. They also lacked data on light
exposure prior to the start of the experiment, which might have
influenced the results.
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“There is a lot of research in both human and animal models that
shows the timing and intensity of prior light exposure can cause a
sort of ‘lighting history’ after-effect on the brain clock,” said
Ilia Karatsoreos, a neuroscience researcher at Washington State
University in Pullman who wasn’t involved in the study. “Thus,
previous exposures to different lighting cycles, and light
intensity, can change the way this clock works.”
Because the current study looked at just one night of bedtime
reading with a tablet and one with a book, and had participants sit
at a desk to read, it’s possible the results would look quite
different in a real-world setting where people might read most
nights in bed before going to sleep, Karatsoreos added by email.
“As most of us know, reading on tablets, checking emails on phones,
or watching late night TV are a chronic issue, and unfortunately
become part of our pre-sleep habits,” Karatsoreos said. “So while
this study seems to argue a single exposure to a tablet does not
have a major effect on sleep if one was also exposed to bright light
beforehand, it doesn’t really address what has become a common
ritual for so many of us.”
SOURCE: http://bit.ly/2bh7ON2 Sleep Medicine, online July 25, 2016.
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