Adolescents who sit for much of the day have a greater risk of depression by the time they reach adulthood, a UK study has found.
Growing numbers of young people with depression and increased time spent sedentary could be two linked trends, researchers at University College London (UCL) believe.
They found that those who did an additional hour of light activity each day, such as walking or chores, saw a reduction in depressive symptoms when they reached 18.
They analysed data on 4,257 adolescents, who were taking part in the University of Bristol’s Children of the 90s cohort study.
The participants wore accelerometers to track their movement for at least 10 hours over at least three days, at ages 12, 14 and 16, except when washing or during water sports.
These devices showed whether the child was sedentary, engaging in light activity such as playing an instrument or moderate to physical activity such as running.
They also answered a questionnaire which measured depressive symptoms such as low mood, loss of pleasure and poor concentration.
Between ages 12 and 16, physical activity declined while sedentary behaviour increased, the study found.
Time spent on light activity decreased from an average of five-and-a-half hours to just over four hours.
Sedentary behaviour rose from an average of just over seven hours to eight hours 45 minutes.
For every additional hour of sedentary behaviour per day at age 12, 14 and 16, the participants’ depression score calculated from the questionnaire rose by 11.1%, 8% or 10.7%, respectively, by age 18.
Those who spent consistently high amounts of time sedentary at all three ages had 28.2% higher depression scores by age 18 than those who were rarely sedentary.
And depression scores were 19.6% lower in participants with consistently high levels of light activity.
Every additional hour of light physical activity per day at age 12, 14 and 16 was associated with depression scores at age 18 that were 9.6%, 7.8% and 11.1% lower, respectively.
At age 18, the questionnaire scores suggested 747 possible cases of depression.
Lead author and UCL Psychiatry PhD student Aaron Kandola said: “Our findings show that young people who are inactive for large proportions of the day throughout adolescence face a greater risk of depression by age 18.
“We found that it’s not just more intense forms of activity that are good for our mental health, but any degree of physical activity that can reduce the time we spend sitting down is likely to be beneficial.
“We should be encouraging people of all ages to move more, and to sit less, as it’s good for both our physical and mental health.”
He added: “Worryingly, the amount of time that young people spend inactive has been steadily rising for years, but there has been a surprising lack of high-quality research into how this could affect mental health.
“The number of young people with depression also appears to be growing and our study suggests that these two trends may be linked.”
The study also involved King’s College London and South London and Maudsley NHS Foundation Trust.
The authors say replacing sedentary behaviour with light activity could be an important public health intervention to reduce cases of depression.
The study’s senior author, Dr Joseph Hayes, from Camden and Islington NHS Foundation Trust, said: “Light activity could be particularly useful because it doesn’t require much effort and it’s easy to fit into the daily routines of most young people.
“Schools could integrate light activity into their pupils’ days, such as with standing or active lessons.”
The study is published in the journal Lancet Psychiatry.