Every extra walk to school, kickabout in the park or trip to the shops could be doing more for teenage mental health than first thought, according to new research tracking thousands of adolescents in the US.
The study, led by King's College London's Institute of Psychiatry, Psychology & Neuroscience, working with the University of Massachusetts Amherst, tracked 5,515 adolescents taking part in the US Adolescent Brain Cognitive Development Study.
Participants wore Fitbit devices for three weeks around age 11 to 12. A year later, researchers checked in on their mental health, using the Child Behaviour Checklist, a widely used questionnaire completed by the young people and their parents that measures symptoms such as anxiety, low mood and behavioural problems, and compared the results against how many steps each teenager had been taking.
The more adolescents walked, the fewer mental health problems they had a year later, and the benefit didn't level off at any point the researchers could measure. Teenagers who took under 5,000 steps a day had the most symptoms; those averaging around 8,000 had fewer; and those hitting 12,000 or more had the fewest of all.
Adolescents with the highest step counts also showed slightly thicker brain tissue in two areas involved in movement and in regulating emotion, and this difference helped explain part of the link to better mental health. There was no link found between step count and how well adolescents did at school.
Dr Divyangana Rakesh, Senior Lecturer in Neuroscience and Psychology, King's College London, and senior author of the study, said:
"This study gives us some of the clearest evidence yet that even an everyday, low-cost, accessible measures of physical activity like daily step count is tied to how adolescent brains and mental health develop. What's striking is that we don't see this benefit levelling off in the observed range, even among the most active young people in our sample."
Qingyang Li, lead author of the study, said:
"We're starting to understand parts of the brain that might be involved in the link between daily steps and young people's mental health. It's preliminary, but it gives us a clearer idea of where to look next."
The study used data from the Adolescent Brain Cognitive Development Study, the largest long-term study of brain development and child health in the US, run across 21 sites. Step counts were measured objectively through wearable devices rather than self-report, which has been suggested to be a more reliable way of capturing habitual activity than questionnaire-based assessments most previous research has relied on.
Dr Amanda Paluch, Associate Professor of Kinesiology, University of Massachusetts Amherst, said:
"Adolescence is a key period for brain development and mental health, so it's encouraging to see that physical activity's benefits extend to both.
"It is not an all-or-nothing situation. Adolescents don't need to be elite athletes to benefit. 1,000 to 2,000 higher daily step increments, from any starting point, was associated with better brain structure and mental health outcomes, and that beneficial association keeps building from there.
"The goal is finding realistic, sustainable ways to move more, through everyday opportunities like walking to school, active play, and activities kids actually enjoy, so these benefits are accessible wherever an adolescent is starting from."
This is an observational study, so it can't show that walking more directly improves mental health. The link held after the researchers took account of the adolescents' earlier mental health problems, though they say it's still possible that those with fewer problems were simply more active to begin with. The brain differences involved were small, and few adolescents in the sample took extremely high step counts, so it isn't yet clear whether the pattern continues beyond what was measured here.
