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Light activity may improve mental health for teenagers

Wednesday 12 February 2020

"Teenagers who sit for hours a day are more likely to get depression at 18," reports the Mail Online.

It's been known for some time that children's activity levels go down as they get older, and this seems to be happening more in recent years. The numbers of teenagers with depression have also been rising.

Researchers tracked the activity levels of 4,257 teenagers aged 12, 14 and 16. They then tested them for symptoms of depression at age 18. During the study, average levels of light activity, such as slow walking, fell. Time spent sitting or lying down increased. More time spent doing light activity at age 12 to 16 was linked to lower depression scores at age 18, while more time spent sitting still was linked to higher depression scores.

Only 1.5% of those in the study were meeting government recommendations for people aged 5 to 18 to do an hour of moderate intensity activity each day.

The researchers say it might be easier for teenagers to do more light activity than to increase the amount of moderate-to-vigorous activity they do. Even the relatively small decreases in depression scores seen in the study could have an important impact on the mental health of some young people.

Find out more about recommended physical activity levels for children and young people.

Where did the story come from?

The researchers who carried out the study were from University College London and King's College London. The study was funded by the Medical Research Council, the Wellcome Trust and the University of Bristol. It was published in the peer-reviewed medical journal Lancet Psychiatry, on an open-access basis, so it is free to read online.

The study is reported with reasonable accuracy and balance by the UK media, although the limitations of the study and possible alternative explanations for the results are not explained.

What kind of research was this?

This was a cohort study. Cohort studies, like other observational studies, are good ways to look at links between risk factors (such as levels of physical activity) and outcomes (such as depression symptoms). But they cannot show that one directly causes another. There may be other factors involved.

What did the research involve?

Researchers in Bristol recruited pregnant women in 1991 to take part in a long-running study (the Avon Longitudinal Study of Parents and Children). The children born as a result of those pregnancies were followed up regularly with health checks and questionnaires.

In this study, researchers looked at groups of teenagers who had at least 1 measure of physical activity taken by a device called an accelerometer at age 12 (2,486 teens), 14 (1,938 teens) or 16 (1,220 teens), and had been tested for symptoms of depression at age 18 (4,257 teens) using the CIS-R depression score computer assessment. They analysed the results for links between depression symptom scores and:

  • total physical activity at age 12, 14, or 16
  • sedentary time (time spent sitting or lying down)
  • light activity (such as slow walking)
  • moderate to vigorous activity (such as running or sports)

They took account of factors including their sex, ethnic background, social class, signs of depression at age 12, IQ, any history of serious mental illness in the parents and parental education level. They also adjusted figures for the amount of time the teenagers wore the accelerometer.

What were the basic results?

The researchers found teenagers spent about an hour and a half (93 minutes) longer each day sitting still or lying down at age 16 compared to age 12. They spent an hour and 20 minutes (81 minutes) less time each day doing light physical activity at age 16 compared with age 12. Time spent doing moderate to vigorous physical activity remained about the same, although it was at a low level (around 20 minutes) from the start.

About 17% to 18% of teenagers had symptom scores that might mean they had depression at age 18.

When researchers looked at time spent sitting still or lying down, they found teenagers who spent more time sitting down had higher depression scores, while teenagers who spent more time doing light activity had lower scores:

  • each additional hour per day spent sitting still at age 12 to 16 was linked to an 11% to 8% increase in depression symptom score at age 18 (incidence rate ratio (IRR) age 12: 1.11, 95% confidence interval (CI) 1.05 to 1.18; IRR age 14: 1.08, 95% CI 1.01 to 1.15; IRR age 16: 1.11, 95% CI 1.02 to 1.21)
  • each additional hour per day spent doing light activity at age 12 to 16 was linked to an 11% to 8% decrease in depression symptom score at age 18 (IRR age 12: 0.90, 95% CI 0.85 to 0.96; IRR age 14: 0.92, 95% CI 0.86 to 0.99; IRR age 16: 0.89, 95% CI 0.81 to 0.97)

The teenagers' moderate-to-vigorous physical activity levels did not seem strongly linked to depression scores. This could be because too few of them were doing sufficient moderate-to-vigorous physical activity to make an impression on the results.

Spending more time, overall, doing physical activity was also linked to lower depression scores.

How did the researchers interpret the results?

The researchers said: "The displacement of sedentary behaviour with light activity in young people warrants more direct and specific consideration in physical activity guidelines and public health interventions aimed at reducing the prevalence of depression." They called for schools to encourage "standing lessons, increasing active travel time between classes, or promoting lightly active hobbies such as playing an instrument and painting."


The link between physical activity and mental health has been investigated for some time. But this is the first study to have looked at accelerometer-measured activity – including light activity – in teenagers and the link to mental health.

Physical activity, whether that's doing household chores or training to run a marathon, has consistently been shown to benefit physical and mental health. A study that shows even light activity may benefit teenager's mental health is therefore welcome.

However, there are some limitations to the study. Physical activity and mental health may both be linked to other factors, such as the environment in which children live, their physical health, social support and the amount of time they spend using a screen. For example, a child who does not have a safe space to be active outdoors may be more likely to spend a lot of time indoors, sitting or lying down, and may also have poorer mental health. It is difficult to say which of these factors is most important.

Teenagers in the study also tended to drop out of physical activity monitoring as the study progressed, meaning there were more records of activity at age 12 than at age 16. This could explain why the links between depression scores and activity levels at age 12 seem stronger than at age 16. There were only 1,220 records of activity at age 16, compared with 2,486 at age 12.

Despite the limits of the study, the message that teenagers should be encouraged to be more active for the sake of their mental health is an important one. Symptoms of depression often emerge for the first time during adolescence. Efforts to stop and reverse the increasing inactivity of children and young people could have important effects on future mental health.

Find out more about signs of depression in young people, and how to get help.

Analysis by Bazian
Edited by NHS Website