By Tara Haelle
THURSDAY, Aug. 7, 2014 (HealthDay News) -- 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.
"Parents and clinicians have to remember that just because there's an association and one preceded the other doesn't mean we can assume there is a causal relationship," Adesman said. "We cannot be sure that improvements in fitness will unequivocally lead to improved mental health based on this study." Yet, he said, it's certainly likely that improved fitness may lead to an improved overall sense of well-being and mood.
The causes of depression are complex, with risk factors that include poverty, violence, poor support from family or friends, self-esteem or body image issues, negative thought patterns, poor coping skills, genetics and difficult life events such as divorce, Ruggero said. "None of these mean a child will get depressed," he said. "Rather these factors just increase the risk of it."
At the same time, both Adesman and Ruggero emphasized that fitness confers other advantages.
"Fitness is, in its own right, an appropriate goal for children, especially in a time when we have an obesity epidemic in our country starting in childhood," Adesman said.
A healthier weight, fewer risk factors for heart disease later in life and, according to some research, better academic performance are all additional benefits of improved fitness, Ruggero added.
He said children and teens are more motivated to be physically active or to participate in sports when it's fun, and they are more likely to drop out when it becomes less enjoyable or they feel more pressure. The key is to focus on improving their own skills and abilities rather than focusing on others' abilities or only outcomes, he said.