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Adolescents who spend too much time sitting still and engaging in sedentary behaviour are at an increased risk of depressive symptoms.

A study published in The Lancet Psychiatry found that even an additional 60 minutes of light activity like walking or doing chores at the age of 12 was associated with a 10 per cent reduction in symptoms of depression by the age of 18.

“We found that throughout adolescence, sedentary behaviour (sitting down with minimal movement) increased throughout adolescence and light activity, anything from gentle housework to walking at a casual pace, decreased. We found that the increases in daily sedentary behaviour during adolescence were associated with a greater risk of depression by 18, while higher light activity were associated with a lower risk of depression at 18,” Aaron Kandola, lead author of the study and a PhD student at UCL Psychiatry told Theravive. 

In undertaking the research, Kandola and colleagues examined data from the University of Bristol’s Children of the 90s cohort study. They focused on data from 4257 adolescents who wore accelerometers to track their movements 10 hours a day for at least three days, across the ages of 12, 14 and 16. 

The accelerometers indicated if the child was engaging in light or moderate physical activity, or if they were sedentary. Light activity could be playing an instrument or painting, moderate to physical activity could be things like running or cycling.

To measure depressive symptoms like loss of pleasure, poor concentration and low mood, the participants completed a questionnaire.

The researchers found that between ages 12 and 16, the amount of total physical activity undertaken by the participants declined. Light activity declined from around five and half hours on average to around four hours.  Sedentary behaviour increased from an average of seven hours and 10 minutes to eight hours and 43 minutes.

Every additional 60 minutes spent being sedentary every day was associated with an increase in depression score of 11.1 per cent at aged 12, 8 per cent at age 14 and 10.5 per cent at age 16. Those who were consistently spending high amounts of time being sedentary across the three ages had depressions scores that were 28.2 per cent higher by age 18.

In contrast, every extra hour of light physical activity per day was associated with a depression score that was 9.6 per cent lower at aged 12, 7.8 per cent lower at age 14 and 11.1 per cent lower at age 16.

“Physical activity can stimulate changes in the brain that improve the way it functions - many of these changes occur in regions of the brain that are related to depression. Physical activity also reduces inflammation, which is another factor that looks to be involved in some cases of depression. There are psychological factors too, it may help with self-esteem or self-efficacy,” Kandola said. 

The researches found moderate to vigorous activity at an early age was associated with reduced depressive symptoms, however the data on this is weaker due to low levels of activity of this kind among the cohort studied.  

Kandola says the research emphasises more needs to be done to get young people and adults alike moving more.

“Developing interventions that help to reduce sedentary behaviour and increase light activity in both young people and adults is a logical next step,” he said.

“The more we learn about the importance of activity the more we have to look at the school system for change. Increasing activity can be done through simple changes that start at school… active classes, active breaks during classes, active homework, increasing the distance between classes, standing desks. We should shape the environment around young people to increase their activity, taking the onus away from parents and young people themselves - it doesn't need to be an individual responsibility.”