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 Following more than 4,000 young people from age 12 to age 18,
researchers found physical activity levels declined as kids got
older. But those who were the most sedentary at ages 12 through 16
were the most likely to have symptoms of depression at 18.
Conversely, kids who maintained or increased light physical activity
across the years had the lowest depression risk at 18.
"Our results suggest young people should aim to reduce their
sedentary behavior and increase their light activity during
adolescence, a time when the opposite tends to occur," said lead
study author Aaron Kandola of University College London in the UK.
"This could reduce the risk of depression in the future."
"Most children should have no trouble finding 60 minutes a day for
activity, whatever form it takes," Kandola said.
The structure of the school day is a major source of inactivity and
sedentary behavior, Kandola said by email.
"Simple changes could be tried to address this, such as
active/interactive classes, active homework, activity breaks in the
middle of lessons, increasing the walking distance between classes,
implementing standing desks for some lessons," Kandola said.
While previous studies have linked exercise to improved physical and
mental health, much of this research has focused on adults and
failed to objectively measure exercise levels, Kandola and his
colleagues note in The Lancet Psychiatry.
For the study, the researchers analyzed data on 4,257 young people
who wore accelerometers for a week when they were 12, 14 and 16
years old. Participants also completed questionnaires designed to
identify any symptoms of depression or other mental health disorders
at age 18.
Accelerometers objectively measured when participants engaged in
light activity like walking or more intense exercise like running or
cycling. The devices also recorded periods when teens were
sedentary, doing things like homework or playing video games.
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Between ages 12 and 16, participants' average daily sedentary time
increased from about seven hours to almost nine hours. Over this
same period, their average daily time devoted to light activity like
walking or doing chores dropped from about five hours to around two
hours.
Each additional hour of sedentary time at ages 12 and 14 was
associated with an 8% to 11% higher risk of depression symptoms by
age 18, the study found. The reverse was also true, with each
additional 60 minutes per day of light physical activity lowering
the odds of depression at age 18 by 8% to 11%.
Even though the study wasn't designed to prove whether or how
sedentary time might compromise mood, or how activity might make
mental health problems less likely, the findings are in line with
past research in adults, the authors note.
It's possible activity improves self-esteem, reduces inflammation or
stimulates the growth of new neurons in the brain, they write.
"Exercise has been linked to neurogenesis (the forming of new brain
cells) and neuroplasticity (ability for the brain to rewire and make
new connections), which can be protective for mental health," said
Karmel Choi, a researcher at Massachusetts General Hospital and the
Harvard T.H. Chan School of Public Health in Boston who coauthored a
commentary accompanying the study.
"When people are getting more physical activity, their bodies also
tend to be less reactive to stress and show lower levels of
inflammation, a risk factor for depression," Choi said by email.
SOURCE: https://bit.ly/324vOcR and https://bit.ly/2HCsNad The Lancet
Psychiatry, online February 11, 2020.
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