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," said lead author George Mammen, PhD candidate from the Faculty of Kinesiology and Physical Education Department at the University of Toronto in Ontario, Canada.
"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.
Previous studies have shown a link between exercise and decreasing symptoms in patients with depression. "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.
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.