November 07, 2013
Even low levels of physical activity may reduce the risk of developing depression in individuals of all ages, new research suggests.
In 25 of 30 large studies examined in the systematic review, which included participants between the ages of 11 and 100 years, a "negative risk" was found between baseline physical activity (PA) and the future development of depression.
In addition, this inverse association was found in all levels of PA ― including less than 2.5 hours of walking per week.
"It was a little surprising that 25 of the studies found this protective effect, and that's really promising," lead author George Mammen, PhD candidate from the Faculty of Kinesiology and Physical Education Department at the University of Toronto in Ontario, Canada, told Medscape Medical News.
"We also did quality assessments on each study, and the majority were of high methodologic quality, which adds weight to the findings," said Mammen.
He noted that the take-home message is that being active is important for more than just physical health.
"From a population health perspective, promoting PA may serve as a valuable mental health…strategy in reducing the risk of developing depression," write the investigators.
The study was published in the November issue of the American Journal of Preventive Medicine.
Prevention Strategy Needed
Previous studies have shown a link between exercise and decreasing symptoms in patients with depression, including several reported by Medscape Medical News.
"However, with the high prevalence of depression worldwide and its burden on well-being and the healthcare system, intuitively, it would make more sense…to shift focus toward preventing the onset of depression," the investigators write.
"We need a prevention strategy now more than ever. Our health system is taxed. We need to…look for ways to fend off depression from the start," added Mammen in a release.
After searching 6 of the top databases, including MEDLINE and PubMed, the researchers found 6263 worldwide citations of PA and depression. For this analysis, they selected 30 English-language studies that were published between January 1976 and December 2012.
All were prospective, longitudinal, and "examined relationships between PA and depression over at least two time intervals." They had follow-up periods ranging from 1 to 27 years.
Results showed that 25 of the studies revealed a significant inverse effect between any PA reported at baseline and subsequent depression development.
Interestingly, 4 of these studies showed that women who reported baseline PA were less likely than men to develop depression.
"These studies postulate that psychological factors may explain these findings because women may benefit more from the social aspects of PA than men," note the investigators.
Of the 5 studies that did not find a significant association between PA and depression, "only 1 was considered to be of high quality," and 2 focused only on older adults.
Using data from the 7 studies that measured amounts of weekly PA participation, the researchers found that exercising more than 150 minutes per week was associated with a 19% to 27% decreased risk of developing depression.
Surprisingly, participating in less than 150 minutes per week of PA was associated with a 8% to 63% decreased depression risk compared with individuals who were sedentary. Still, the 63% decreased risk was found in one study of patients participating in 120 minutes of weekly PA.
The current guidelines for PA by adults, released by the Canadian Society for Exercise Psychology, recommend 150 weekly minutes of moderate to vigorous activity.
Two other studies assessed daily amounts of PA. One showed that 10 to 29 minutes a day of PA was associated with a risk ratio (RR) of 0.90 for depression onset, whereas 60 to 90 minutes of daily PA had an RR of 0.84, and more than 90 minutes of daily PA had an RR of 0.80.
The other study showed that participating in more than 30 minutes of daily PA reduced the odds of depression onset by 48%.
In addition, 3 of the 4 studies that examined walking status showed that it was protective against depression, with 2 suggesting that even low levels of walking decreased risk for depression by almost 60%.
Nine of the 11 studies that examined PA levels over time showed a significant association with depression onset, with 5 suggesting that reducing PA levels increased the risk for onset, and 4 suggesting that increasing or maintaining PA levels reduced the risk.
"The majority of [the studies] were of high methodologic quality, providing a solid indication that PA may prevent future depression," write the investigators.
They note that the evidence shows this indication even with low levels of PA.
"At the least, current guidelines for PA, established for physical health benefits, appear equally appropriate for preventing depression," they write, adding that individuals should maintain or increase their current activity levels to continue staving off the threat of depression development.
"And if you're not physically active, you should initiate the habit. This review shows promising evidence that the impact of being active goes far beyond the physical. Even just walking to the grocery store or walking to work for 20 minutes would be great," said Mammen.
Exciting Area of Research
"I think the authors did a very good job of compiling longitudinal evidence supporting [PA] reducing the onset of future depression," Chad D. Rethorst, PhD, assistant professor in the Department of Psychiatry at the University of Texas Southwestern Medical Center in Dallas, told Medscape Medical News when asked for comment.
"They also did a good job of pointing out some potential weaknesses of the research that is currently available," he added. These included the fact that most of the studies relied on personal report of PA levels.
"So we have a hard time teasing out how true the relationships are in these observational studies and how accurate the self-report measures are."
Dr. Rethorst, who was not involved with this research, has written before about the association between high levels of PA, as measured objectively by an accelerometer, and decreasing depressive symptoms in an older population.
He noted that the current study's suggestion that PA might help prevent depression is "definitely an exciting area" and will garner future attention.
"However, it's limited right now to these observational, longitudinal studies. And that's because predicting the onset of depression is so difficult," he explained.
"Identifying people who are at a higher risk for depression is something the field of psychiatry has been able to do a bit. Family history or previous episodes of depression are related to an increased risk of future risk. However, there's a lot of unexplained variances in predicting future depression right now."
That is why it is important for future randomized, controlled trials to objectively examine PA in individuals who are at risk, said Dr. Rethorst. Unfortunately, he added, that would require very large samples.
"The evidence for using exercise to treat depression is currently stronger than the evidence showing it is able to prevent depression," he said.
For now, he noted that "it wouldn't hurt" for clinicians to suggest exercise to their patients.
"The research shows that activity is good not only for depression but for a large number of physical conditions. It has a lot of benefits. So recommend physical activity for all patients, regardless of current depressive symptoms or potential risk factors for these symptoms," said Dr. Rethorst.
The study was funded in part by a Population Level Interventions for Chronic Disease Prevention training grant from the Canadian Institute for Health Research. The study authors and Dr. Rethorst have disclosed no relevant financial relationships.