The more fit middle-school girls are, the less likely they may be to develop symptoms of depression, according to a recent study.

Although the effect of fitness on depression was small, improvements in fitness may be part of an overall strategy for reducing the risk of depression in middle-schoolers, according to Camilo Ruggero, lead researcher and an assistant professor of psychology at the University of North Texas. Other strategies might include school-based or family therapy, which can both treat and help prevent depression in at-risk kids.

“Fitness is not a cure-all, but it’s a small piece of a larger problem,” said Ruggero. He noted that depression is also linked to a higher body mass index (BMI), a measurement used to assess if a person has a healthy weight for their height. In addition, middle school is a time when fitness levels drop off, weight increases and depression increases. “That’s why we’re so focused on that period,” he said.

“We don’t know exactly why there is a link (between fitness levels and depression), but it is probably a number of things,” Ruggero said. “It might be better self-esteem, healthier weight or getting more positive reinforcements that go along with being active, and/or it could be more biological. We know certain proteins and hormones associated with less depression respond to increased exercise.”

He said the relationship might be reciprocal, too: the researchers also found that depression among sixth-grade boys predicted poorer fitness in seventh grade.

There was also a trend between fitness levels and depression in boys but it was not statistically significant. Less depression occurs among boys in general, so the effect may have been harder to detect, according to Ruggero. He suspects a study using a larger number of boys might show a stronger link, though it would likely still be modest.

The findings were presented Thursday at the annual meeting of the American Psychological Association in Washington, D.C. Findings presented at meetings are generally considered preliminary until they’ve been published in a peer-reviewed journal.

For the study, the researchers gauged the fitness of more than 400 North Texas sixth-graders based on how many shuttle runs they could complete within a specified amount of time and their own assessment of their physical strength and endurance.

The strongest predictor of depression symptoms in girls was a history of depression, but even after accounting for past depression and BMI, higher fitness levels in sixth grade were linked to a lower likelihood of depression in seventh grade.

Past research has found conflicting results about potentially protective effects of fitness on depression, but those inconsistencies may stem from using physical activity instead of “cardiorespiratory fitness” as a measure. The amount of physical activity a person gets from one week to the next can vary greatly, but overall fitness results from sustained physical activity over time.

Still, this study could not show that better fitness levels directly prevented depression, cautioned Dr. Andrew Adesman, the chief of developmental and behavioral pediatrics at Cohen Children’s Medical Center of New York.

This article first appeared on ‘News Star’ on 10 August 2014.