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 Researchers asked 18 adolescents who regularly got 5 to 7 hours of
rest a night to go to bed early and get an extra 1.5 hours of sleep
on school nights for two weeks and wear activity trackers during the
day. During a separate two-week period, researchers tracked the
teens' activity levels when they stuck to their habitual bedtimes
and got their regular amount of sleep.
When they had to get extra rest, teens averaged 71 more minutes of
sleep on school nights than they did before they started the
experiment.
With this extra sleep, teens spent an average of 52 fewer minutes of
the day being sedentary than they did when they were asked to follow
their usual sleep schedules. But the amount of time they devoted to
light or vigorous physical activity didn't change much based on how
much rest they got, according to the results in Sleep Medicine.
"When teens sleep less, they spend more time awake, and we knew that
something had to occupy that 'extra' time," said lead study author
Tori Van Dyk of Cincinnati Children's Hospital Medical Center.
"It turns out that extra time awake is almost all just sitting
around - it has no health benefits," Van Dyk said by email. "In
contrast, when teens sleep more, they replace sedentary behavior
with sleep, which we know is helpful for thinking skills, physical
health, safety and mood."
Ideally, teens should get 8 to 10 hours of sleep each night,
according to the U.S. Centers for Disease Control and Prevention
(CDC). They should also get an hour a day of moderate to vigorous
intensity aerobic exercise.
Teens in the study didn't measure up very well against these
recommendations. Some of them didn't get enough rest to begin with
for the extra 1.5 hours to be sufficient.
And whether or not they got extra rest, they still came up far short
of the meeting the CDC exercise targets. When the teens got their
typical amount of sleep, they averaged a total of about 245 minutes
of light and vigorous exercise over five weekdays, when they should
have had 300 minutes of moderate to intense activity. With extra
sleep, they averaged about 225 minutes of light and vigorous
exercise.
The difference in exercise with the two different sleep schedules
wasn't big enough to rule out the possibility that it was due to
chance.
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One drawback of the experiment, however, is that it only had 18
participants and it's possible that a larger group might have
highlighted meaningful differences in exercise based on the amount
of sleep they got. Many teens also failed to follow the directions
for their sleep routines during the study.
"The study shows that although teenagers can be stubborn it appears
possible to modify their sleeping habits," said Dr. Paul Collings of
the Bradford Institute for Health Research in the UK.
"This is reassuring - but we must bear in mind that the study lasted
only a few weeks and involved a small and select group of
teenagers," Collings, who wasn't involved in the study, said by
email.
It's still encouraging that teens in the study didn't appear to
sacrifice exercise to get more sleep, said Michelle Garrison of the
University of Washington and Seattle Children's Research Institute.
"This is great news, since sometimes improving one aspect of health
can come at the cost of slipping in other areas, and so it's
wonderful to see that improving sleep doesn't affect physical
activity in teens this age," Garrison, who wasn't involved in the
study, said by email.
While parents can't always control all the things that get in the
way of a good nights' sleep for their teens - whether it's the
demands of jobs or sports or the early start of the school day -
they can still help support good sleep habits, said Jonathan
Mitchell, a researcher at the University of Pennsylvania and the
Children's Hospital of Philadelphia.
"Parents do oversee the environment where the vast majority of sleep
periods occur," Mitchell, who wasn't involved in the study, said by
email. "Removing screens from their bedrooms and enforcing strict
bedtime routines have been consistently shown to be associated with
more sufficient sleep among children."
SOURCE: https://bit.ly/2r21jmi Sleep Medicine, online March 29,
2018.
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