Declining Physical Activity at Age 12 Tied to Depression at 18

Michael Vlessides

February 20, 2020

Declining physical activity starting at age 12 is associated with depressive symptoms at age 18, new research shows.

In the first study to objectively measure physical activity in teens, investigators found that every additional 60 minutes of sedentary behavior per day at age 12, 14, and 16 was linked to an increase in depression scores of 11.1%, 8%, and 10.7%, respectively at age 18.

Conversely, every additional hour of light activity per day at age 12, 14, and 16 was tied to a decrease in depression scores of 9.6%, 7.8%, and 11.1%, respectively, when measured at age 18.

"We showed that there was a consistent association between sedentary behavior and depressive symptoms, which has been quite hard to study. Traditionally, sedentary behavior is measured using questionnaires, which tend not to be particularly reliable," study investigator and PhD candidate Aaron Kandola, University College London, United Kingdom, told Medscape Medical News.

The use of accelerometers, which automatically record movement, allowed the researchers to examine physical activity with much greater accuracy, he added.

The study was published online February 11 in Lancet Psychiatry.

Rising Rates of Teen Depression

The investigators note that depressive symptoms often surface during adolescence and may offer a critical time frame at which to head off depression. Furthermore, a recent US study showed the prevalence of depression in teens has increased from 8.7% in 2005 to 11.3% in 2014.

Although there is growing evidence suggesting physical activity may reduce the symptoms of depression in both clinical and nonclinical populations, research in adolescents has been sparse.

"A lot of the research to date has been done in adults," said Kandola. "But we know that the onset of depression and anxiety disorders tends to be earlier than that. And we didn't actually know a whole lot about the relationship between activity and depression in young people."

What's more, almost all of the previous studies in teens have used self-reported measures of physical activity, which are subjective, tend to underestimate sedentary behavior, and rarely account for light-intensity activities such as walking.

To gain a more precise understanding of physical activity in teens and the potential link to depressive symptoms as youth move into adulthood, the investigators examined data from the Avon Longitudinal Study of Parents and Children (ALSPAC) study, which followed children born between April 1991 and December 1991.

Using accelerometers, the investigators objectively measured various forms of physical activity at three points during adolescence and then measured depressive symptoms when participants were 18 years old.

"It's quite a crucial time to look at, because we know that people tend to see a decline in their activity and an increase in sedentary behavior as they move through adolescence," said Kandola.

A Little Movement Makes a Big Difference

The analysis included 4257 adolescents with at least one accelerometer recording and a Clinical Interview Schedule-Revised (CIS-R) depression score at age 18.

Participants wore accelerometers to track their movement for at least 10 hours over three days at ages 12 (n = 2486), 14 (n = 1938) and 16 (n = 1220).

The accelerometers allowed objective assessment of light physical activity (such as walking or engaging in hobbies) and moderate physical activity (such as running or cycling) as well as sedentary behavior.

Results showed that between the ages of 12 and 16, physical activity declined across the cohort; this was primarily driven by a decrease in light activity, which went from an average of 5 hours 26 minutes per day to 4 hours 5 minutes per day. 

In addition, the investigators found sedentary behavior increased from an average of 7 hours 10 minutes per day to 8 hours 43 minutes per day.

Higher depression scores at 18 years were associated with a 60 minute-per-day increase in sedentary behavior at 12 years (incidence rate ratio [IRR], 1.111; 95% confidence interval [CI], 1.051 - 1.176); 14 years (IRR, 1.080; 95% CI, 1.012 - 1.152); and 16 years of age (IRR, 1.107; 95% CI, 1.015 - 1.208).

Conversely, depression scores among 18-year-olds were lower for each additional 60 minutes of daily light activity at 12 years (IRR, 0.904; 95% CI, 0.850 - 0.961), 14 years (IRR, 0.922; 95% CI, 0.857 - 0.992), and 16 years of age (IRR, 0.889; 95% CI, 0.809-0.974).

Classrooms a Good Place to Start

When the investigators performed group-based trajectory modeling on participants from 12 to 16 years of age, they identified three latent subgroups of sedentary behavior and activity levels.

As part of this analysis, depression scores were found to be greater among adolescents with persistently high sedentary behavior (IRR, 1.282; 95% CI, 1.061 - 1.548) and persistently average sedentary behavior (IRR, 1.249; 95% CI, 1.078 - 1.446) than among their counterparts with persistently low sedentary behavior.

In the same vein, depression scores were lower among adolescents with persistently high levels of light activity (IRR, 0.804; 95% CI, 0.652 - 0.990) than among those with persistently low levels of light activity.

Finally, moderate-to-vigorous physical activity (per 15-minute daily increase) at age 12 (IRR, 0.910; 95% CI, 0.857 - 0.966) and total physical activity (per 100 count per minute increase) at ages 12 (IRR, 0.941; 95% CI, 0.910 - 0.972) and 14 (IRR, 0.965; 95% CI, 0.932 - 0.999), were both negatively associated with depressive symptoms.

These findings, the investigators note, suggest interventions targeting sedentary behavior during adolescence may have important public health benefits.

Strategies to increase physical activity should focus more directly on its potential benefits for mental health to improve youth adherence to physical activity guidelines, which is currently low.

Kandola suggested the classroom would be a good place to start.

"In traditional school systems, we've made it quite easy for adolescents to sit down all day. Yet there are some easy fixes," he said

He suggested, "shaping the classroom environment" via potential innovations such as standing desks or regularly scheduled activity breaks during class time.

The Right Move

In an accompanying editorial, Karmel W. Choi, PhD, and Jordan W. Smoller, MD, ScD, colleagues in the Department of Psychiatry at Massachusetts General Hospital in Boston, note that the findings are not all bad news.

"The good news from this study is the implication that light activity — which can include movements as simple as standing, stretching, or casual walking — might be an effective strategy for decreasing the burden of adolescent depression," they write.

"As exhortations to move more and sit less become more common, it is also worth noting that the optimal intensity (and perhaps even duration and types) of physical activity might depend on which outcome we are trying to target," the editorialists add.

"More vigorous activity might indeed be most beneficial for physical outcomes such as bone health or adiposity, whereas, for depression, lighter activity might be sufficient or even preferable."

Finally, Choi and Smoller point out that public health benefits will only be realized when behaviors begin to align with a growing body of evidence supporting the many benefits of physical activity.

"Identifying major drivers of sedentary behavior in adolescents, as well as potential sources of light activity in their daily lives, could enhance the design of targeted prevention strategies," they write. "For now, the data suggest that, when it comes to depression, a broad spectrum of physical movement — including light activity — is probably the right move."

Kandola agreed. "Obviously there is no one silver bullet here, but anything that we can do to reduce the risk is fantastic," he said.

The collection of data used in the study was funded by the UK Medical Research Council and the Wellcome Trust. Kandola has disclosed no relevant financial relationships. Study author Brendan Stubbs has received consultancy fees from ASICS Europe BV. Editorialists Choi and Smoller have disclosed no relevant financial relationships.

Lancet Psychiatry. Published online February 11, 2020. Full text, Editorial

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