Too much time sitting down may trigger depression in teenagers, research suggests.
Scientists from University College London had more than 4,200 adolescents aged 12, 14 or 16 wear fitness trackers for at least 10 hours over three days.
They found that for every additional hour of “sedentary behaviour” a day, the teenager’s risk of depression at 18 rose by up to 11%.
“Worryingly, the amount of time 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”, said lead author Aaron Kandola.
“The number of young people with depression also appears to be growing and our study suggests these two trends may be linked.
“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.”
Mental health among young people is increasingly emerging as a serious issue.
One in nine children aged five-to-15 in the UK battled some mental-health disorder in 2017.
In the US, 3.2% (1.9 million) of children between three and 17 have been diagnosed with depression alone.
The NHS recognises the important of exercise in relieving depression, with work outs releasing “feel-good” endorphins.
To learn more, the scientists looked at teenagers aged 12, 14 or 16 when they took part in the University of Bristol’s Children of the 90s study.
Fitness trackers recorded whether the youngsters took part in light activity - like walking or painting - or moderate-to-physical activity - such as running or cycling.
Questionnaires uncovered any depressive symptoms, like low mood or poor concentration.
Results, published in The Lancet, revealed the teenagers became less active between the ages of 12 and 16.
During this time, light activity went down from an average of five hours, 26 minutes a day to four hours, five minutes.
Sedentary behaviour also increased from seven hours, 10 minutes to eight hours, 43 minutes.
For every additional hour of sedentary behaviour at 12, 14 and 16, depression scores at 18 rose by 11.1%, 8% and 10.5%, respectively.
The participants with consistently high sedentary behaviours from 12-to-16 had a 28.2% greater score at 18.
In contrast, every extra hour of light activity at 12, 14 and 16 reduced a participant’s depression score at 18 by 9.6%, 7.8% and 11.1%, respectively.
The results remained true after the scientists adjusted for socioeconomic factors, parental mental health and wellbeing at the start of the study.
Low levels of moderate-to-physical activity overall left the scientists unable to gauge its effects on mood down the line.
“A lot of initiatives promote exercise in young people, but our findings suggest that light activity should be given more attention as well,” said study author Dr Joseph Hayes.
“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.
“Small changes to our environments could make it easier for all of us to be a little bit less sedentary.”