We all know that aerobic exercise is an effective treatment against depression. Yet, many people who would profit from more exercise do not do it because they do not understand how physical exercise can impact a mental state.
Recent research has addressed the question.
Gretchen Reynolds reports in The New York Times:
Scientists have also known that exercise seems to cushion against depression. Working out somehow makes people and animals emotionally resilient, studies have shown.
But precisely how exercise, a physical activity, can lessen someone’s risk for depression, a mood state, has been mysterious.
How do scientists diagnose depression in mice?
We can’t ask mice if they are feeling cheerful or full of woe. Instead, researchers have delineated certain behaviors that indicate depression in mice. If animals lose weight, stop seeking out a sugar solution when it’s available — because, presumably, they no longer experience normal pleasures — or give up trying to escape from a cold-water maze and just freeze in place, they are categorized as depressed.
Submit the mice to stress and they develop symptoms that characterize depression.
But, isn’t that an interesting suggestion in and of itself? Presumably, the mice do not have the mental means to do more than suffer the stress. Human beings, however, do not necessarily turn stress into depression. They can adapt to stress; they can manage stress; they can avoid it; they can submit to it.
In other words, human beings have free will. Subjected to stress they might withdraw from life and hole up in their rooms. But they can find other ways to manage and to overcome stress.
As for the scientific findings, Reynolds writes:
A wealth of earlier research by these scientists and others had shown that aerobic exercise, in both mice and people, increases the production within muscles of an enzyme called PGC-1alpha. In particular, exercise raises levels of a specific subtype of the enzyme known unimaginatively as PGC-1alpha1. The Karolinska scientists suspected that this enzyme somehow creates conditions within the body that protect the brain against depression.
So the scientists looked for which processes were being most notably intensified in their PGC-1alpha1-rich mice. They found one in particular, involving a substance called kynurenine that accumulates in human and animal bloodstreams after stress. Kynurenine can pass the blood-brain barrier and, in animal studies, has been shown to cause damaging inflammation in the brain, leading, it is thought, to depression.
But in the mice with high levels of PGC-1alpha1, the kynurenine produced by stress was set upon almost immediately by another protein expressed in response to signals from the PGC-1alpha1. This protein changed the kynurenine, breaking it into its component parts, which, interestingly, could not pass the blood-brain barrier. In effect, the extra PGC-1alpha1 had called up guards that defused the threat to the animals’ brains and mood from frequent stress.
I will leave the brain science to others, but if exercise can modify brain chemistry, perhaps changes in the way one deals with stress can do so as well.