There's been some discussion among mental health professionals in recent years about depression as a “luxury disorder,” far more prevalent in wealthy countries - especially the United States - than in the developing world. The idea is that once basic survival issues are out of the way, the demons of depression are more likely to set in.
But depression is no longer just a problem in the traditionally wealthy nations of the global north. It's on the rise across the world. According to 2012 figures from the World Health Organization, more than 350 million people around the planet suffer from the illness, making it the leading cause of disability in the world. One million people commit suicide every year, and depression is a significant contributing factor to that toll.
The question of how to treat, or better yet prevent, this sometimes crippling condition is gaining new urgency as a public health issue.
Now a new review of 30 studies about the link between physical activity and depression, conducted by researchers at the Alberta Centre for Active Living, adds to the case that engaging in such simple human activities as walking and gardening for as little as 20 minutes a day can help to stave off depression. The researchers, Guy Faulkner and George Mammen of the University of Toronto, found that 25 of the 30 studies - which all measured levels of depression over time - showed that physical activity "prevented the onset of depression in the future."
People who entered the studies with higher baseline levels of activity "had a significant decreased risk of developing depression at follow-up," between 8 and 63 percent. Perhaps even more tellingly, people who had lower levels of activity when the studies began "had a significant increased risk of developing depression at follow-up," between 6 and 34 percent.
One study examined by the researchers found that subjects who engaged in light activity such as gardening or walking for a total of only 120 minutes week were at a 63 percent less risk of developing depression.
The findings are significant because of what they suggest about the "luxury" connection with depression. It's not just that the struggle to survive wards off existential dread, as some have theorized. Preventing depression also increasingly appears to be a question of movement, the kind of movement that humans evolved to perform and that is eliminated from everyday life by machines, hired labor, and automobiles. Modern sedentary lifestyles have also been linked with anxiety. And anxiety and depression have their own tangled connection.
The Alberta Centre team comes to what seems like a very common sense conclusion: "From a population health perspective, promoting [physical activity] may serve as a valuable mental health promotion strategy in reducing the risk of developing depression." In light of these findings, the question of how we move around our cities - especially the new ones being built and expanded every day in the developing world - takes on even greater urgency. Because depression is a “luxury” no society can afford.