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 But the time it took to fall asleep and time spent sleeping were
similar under both conditions.
“Since light has an alerting effect, we predicted a lower sleepiness
in the iPad condition at bedtime compared to the book condition,”
said lead author Janne Gronli of the University of Bergen in Norway.
But it was surprising that the iPad light did not delay sleep
initiation, she said.
However, "we found a delay of 30 minutes in the generation of the
restorative slow waves during sleep in the iPad condition,” Gronli
told Reuters Health by email.
The study included 16 nonsmokers ages 22 to 33 who were familiar
with tablets and had no sleep, medical or psychiatric disorders. For
a week before the study began, they were instructed to keep to a
regular sleep-wake schedule and to stay in bed at least as long as
they needed to sleep.
During the study, in which participants slept in their own beds, the
researchers took polysomnographic recordings for three nights of
sleep: one to collect a baseline of how each person slept, one night
of reading from an iPad for 30 minutes before turning out the light
and one night of reading from a book for the same amount of time.
On the night they read from a book, the participants used ordinary
reading light in their bedrooms.
The polysomnographic recordings, including electroencephalograms to
measure brain electrical activity, collected data on total sleep
time, sleep efficiency, percentage of time spent in each sleep
stage, and other aspects of sleep quality during the time between
lights off and sleep onset as well as the time between sleep onset
and first period of REM (rapid eye movement) sleep.
A light meter measured illumination at eye level while the
participants were reading in each condition. Illumination was about
twice as high while reading from the iPad compared to the book, and
the iPad emitted a high level of blue light, the researchers note.
Bedtime and the time at which people got up from bed were similar in
both conditions, with an average sleep duration of slightly less
than eight hours on both days.
Participants said they felt sleepier when reading the physical book,
as reported in Sleep Medicine. After reading from an iPad, EEG
readings showed delayed and reduced slow wave activity, representing
deep sleep, in the brain after sleep onset compared to when the
participants had been reading from a book.
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The eye absorbs short wavelength blue light and signals to the brain
that it is daytime by triggering waking and alerting active brain
areas, Gronli said.
“Slow wave sleep EEG activity is important for the restorative
effect of our sleep,” she said.
The brain’s ability to synchronize cortical activity and generate
slow waves with high amplitude when we sleep improves memory and
cognitive performance, she said.
“The effects are not completely huge,” Samer Hattar of Johns Hopkins
University in Baltimore told Reuters Health.
And since the researchers only measured illumination, they could not
compare the “structure” of the iPad light to regular bedroom light,
Hattar said. Some indoor light bulbs also emit a great deal of blue
light while others do not.
“We only examined one night using an iPad,” Gronli said. “It is
tempting to speculate that daily use of an iPad, and other blue
light emitting electronic devices, before bedtime may have
consequences for human sleep and cognitive performance.”
“To avoid increased activation before bedtime the bedroom should be
used to sleep in, not for work or being on social media,” she said.
A new Apple OS update includes a nighttime mode, which takes into
account the effects of too much blue light in the late evening by
filtering it out, said Christian Cajochen, head of the Center for
Chronobiology at the University of Basel in Switzerland who was not
part of the new study.
“There is also an app called f.lux which does exactly the same,”
Cajochen told Reuters Health by email.
SOURCE: http://bit.ly/1nwuKIj Sleep Medicine, online March 1, 2016.
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reserved.] Copyright 2016 Reuters. All rights reserved. This material may not be published,
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