Adolescents who took more daily steps had fewer mental health problems a year later, in a US study of 5,515

Eleven- and twelve-year-olds who took more steps each day reported fewer mental health problems a year later, according to a study that put step counters on 5,515 American adolescents and scanned their brains. The more they walked, the lower their scores, and the researchers saw no level beyond which the link disappeared.

The study found something in the scans as well. Young people who moved more had slightly thicker tissue in two small regions of the brain’s outer layer. It found nothing in the classroom: step count had no relationship with school grades.

The work was published on October 1 in JAMA Network Open by researchers at King’s College London and the University of Massachusetts Amherst. It is an observational study, and the links it reports are small.

How adolescents’ steps and mental health were measured

The data come from a long-running American project, the Adolescent Brain Cognitive Development (ABCD) Study, which has followed thousands of children since they were 9 or 10 with questionnaires, tests and brain scans. The ABCD Study was conducted across 21 sites across the US.

At about age 11 to 12, the young people were given step counters. Participants wore Fitbit Charge 2 devices on the wrist for 3 weeks to monitor daily step counts. This study included 5515 adolescent participants, and their average was 9,595 steps a day.

That makes the measurement stronger than in most earlier research, which asked young people how active they had been. The university’s summary notes that step counts were measured objectively through wearable devices rather than self-report.

One year later the participants filled in a questionnaire about themselves. It was a 19-item measure of internalizing, externalizing, and attention symptoms. Internalizing means problems turned inward, such as anxiety and low mood. Externalizing means problems turned outward, such as aggression and rule-breaking. School performance was measured using the average of parent- and youth-reported school grades.

What the step counts showed about mental health

Higher step count was associated with lower total mental health problems. The size of the link, in the standardized units the paper uses, was minus 0.080, with a plausible range of minus 0.109 to minus 0.052. On that scale minus 1 would mean problem scores fell in exact step as step counts rose, and 0 would mean no relationship.

The researchers checked the obvious objection, that children who were already struggling might walk less. The link held after the researchers took account of the adolescents’ earlier mental health problems, the release says. They also adjusted for family income and for neighborhood conditions such as disadvantage and access to green space.

They then split the group by step count to see whether the link leveled off. They report that it did not: each higher step category was associated with fewer mental health problems compared with the under 5000 steps group.

That differs from the pattern for physical health. The authors point to previous studies suggesting a plateau in physical health benefits for children and young-to-middle-aged adults around 8000 steps.

Amanda Paluch of the University of Massachusetts Amherst, a co-author who studies step counts, put the result this way. “It is not an all-or-nothing situation. Adolescents don’t need to be elite athletes to benefit,” Paluch said.

What the brain scans of active adolescents showed

The cortex is the folded outer layer of the brain, a few millimeters thick, where most of its processing happens. Cortical thickness, meaning how thick that layer is at a given spot, is one of the things a scan can measure.

Across the brain as a whole there was no difference. Higher step count was not associated with average cortical thickness, total surface area, or total cortical volume. Deeper structures that the team had expected to be larger in active children were not.

Two specific regions did differ. Greater daily step count was also associated with higher cortical thickness in the paracentral and rostral anterior cingulate. Their functions fit the story loosely. The paracentral lobule acts as a medial sensorimotor hub for lower-limb motor control and somatosensory processing, which is to say it handles movement and sensation in the legs. The rostral anterior cingulate cortex is involved in response conflict during information processing, the work of choosing between competing responses.

Thicker is not simply better at this age. The cortex normally thins as children grow up. Cortical thickness typically decreases during normative development, the authors note, normative meaning typical. The authors suggest that thicker tissue in more active children may reflect a slower pace of that thinning, and they add that only repeated scans over time could show it.

The team then asked whether the brain difference could account for the mental health difference. In their model, paracentral thickness statistically mediated the association between higher daily step count and fewer mental health problems 1 year later. Mediated means that part of the link between steps and mental health ran through the brain measure in the statistics. It does not show that walking thickened the cortex or that a thicker cortex protected anyone.

Lead author Qingyang Li was measured about it. “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,” Li said.

When the brain result was examined by step category, it weakened. Only the most active group, at 12,000 steps or more, differed clearly from the least active, and the authors note the absence of consistent stepwise differences across intermediate categories.

No link between steps and school grades

The team had expected more active children to do better at school, as earlier studies suggested. The children did not. Higher step count was associated with fewer mental health problems but not academic performance 1 year later.

The authors offer an explanation without testing it. Schoolwork draws on mental skills that earlier research ties to harder exercise. This may suggest that improvements in academic outcomes require higher-intensity physical activity rather than daily movement alone, they write. Grades also depend on teaching, testing and much else that a step counter does not see.

Where this fits: physical activity and adolescent mental health

A study that watches cannot say what would happen if teenagers were made to move more. Trials can, and some exist. A 2023 analysis pooled them: twenty-one studies involving 2441 participants, with an average age of 14. Physical activity interventions were associated with a reduction in symptoms of depression compared with the control condition. The effect was modest, and it may not last. Analysis of the follow-up outcomes in 4 studies revealed no differences between the physical activity and control groups.

Those trials tested organized programs, mostly several sessions a week of exercise. The new study concerns something more ordinary, the total movement in a child’s day.

Most teenagers move less than health agencies advise. The World Health Organization’s 2020 guidelines state that among children and adolescents, an average of 60 min/day of moderate-to-vigorous intensity aerobic physical activity across the week provides health benefits. That is an hour a day of activity that raises the heart rate. The same guidelines stress that some physical activity is better than none.

An analysis led from that agency measured how many meet the mark. The researchers used data from 298 school-based surveys from 146 countries, territories, and areas. In 2016, 81% of students aged 11 to 17 were insufficiently physically active, 78% of boys and 85% of girls.

Step counts tell a similar story across the teenage years. A review of studies using pedometers, as step counters are known, concluded that daily steps fall steadily through adolescence until approximately 8,000-9,000 steps/day are observed in 18-year olds. It estimated that for adolescents, 10,000 to 11,700 may be associated with 60 minutes of moderate-to-vigorous activity, the guideline amount. The average in the new study, about 9,600, sits just under that range.

What remains open after the adolescent step study

It cannot show cause. The authors say so directly: this is an observational study and causal conclusions cannot be drawn; residual confounding and bidirectional associations remain possible. Residual confounding means other influences the study could not fully account for. Bidirectional means the arrow could point either way. A child who feels well may go out more, and adjusting for a questionnaire score from a year earlier does not rule that out.

Steps are a partial measure of activity. Daily step counts primarily capture ambulatory activity and may not reflect higher-intensity or multicomponent activities, such as organized sports or unstructured play. Ambulatory means done on foot. A child who swims or cycles would be undercounted.

The outcome was a short questionnaire, not a diagnosis. Mental health and academic outcomes were based on self-reported measures, with grades reported by the children and their parents and not taken from school records.

The brain analysis has a statistical weakness the authors name. They picked the two regions and then tested their role in the same group of children, and selecting candidate mediators in the same sample may have inflated the estimated indirect effects. Put plainly, choosing the regions and testing them on the same children can make a result look stronger than it is.

The step counts came from three weeks in one year of each child’s life, and the scans were taken once. Nothing here shows a brain changing over time.

The university’s release adds a limit at the top of the range. Few adolescents in the sample took extremely high step counts, it says, so the pattern beyond what was measured is unknown.

Senior author Divyangana Rakesh of King’s College London said daily step count “is tied to how adolescent brains and mental health develop”. The study itself scanned each child once and did not follow development over time.

In 5,515 American adolescents, more steps a day went with slightly fewer mental health problems a year later and with small differences in two brain regions, in a study that observed and did not intervene.