Some ideas seem so nice, so inoffensive and so harmless, that it seems a shame to criticize them.
Take the idea that exercise is a useful treatment for depression. It's got something for everyone.
For doctors, it's attractive because it means they can recommend exercise - which is free, quick, and easy, at least for them - instead of spending the time and money on drugs or therapy. Governments like it for the same reason, and because it's another way of improving the nation's fitness. For people who don't much like psychiatry, exercise offers a lovely alternative to psych drugs - why take those nasty antidepressants if exercise will do just as well? And so on.
The authors took a large community sample of Norwegian people, the HUNT-2 study, which was done between 1995 and 1997. Over 90,000 people were invited to take part and full data were available from over 40,000.
What they found was that there was an association between taking part in physical exercise as a leisure activity, and lower self-reported symptoms of depression. It didn't matter whether the activity was intense or mild, and it didn't really matter how often you did it: so long as you did it, you got the benefit.
Crucially, however, the same was
not true of physical exercise which was part of your job. That didn't help at all, and indeed the most strenuous jobs were associated with
more depression (but less anxiety, strangely).
How does this fit with the very popular idea that exercise helps in depression? Well, many randomized trials have indeed shown exercise to be better than not-exercize for depression, but the problem is that these trials are never really placebo controlled. You can usually tell whether or not you're going jogging in the park every morning.
So the direct effects of exercise per se are hard to distinguish from the social and psychological meaning of "exercise". Knowing that you're starting a program of exercise could make you feel better: you're taking positive action to improve your life, you're not helpless in the face of your problems. By contrast, doing heavy work as part of your job, while physiologically beneficial, is unlikely to be so much fun.
This doesn't mean that telling people to get more exercise isn't a good idea, but if the meaning of exercise is more important than the physiology, that has some big implications for how it ought to be used.
It's good news for people who just can't take part in strenuous physical exercise because of physical illness or disability, something which is quite common in mental health. It suggests that these people could still get the benefits attributed to exercise even if they did less demanding forms of meaningful activity.
But it's bad news for doctors tempted to default to "get out and go jogging" whenever they see a potentially depressed person. Because if it's the meaning of exercise that counts, and you recommend exercise in a way which sounds like you're dismissing their problems, the meaning will be anything but helpful.
In clinical trials of exercise, the exercise program has, almost by definition, a positive value: it's the whole point of the trial. And the participants just wouldn't have volunteered for the trial if they didn't, on some level, think it would make them feel better.
But not everyone thinks that way. If you go to your doctor looking to get medication, or psychotherapy, or something like that, and you're told that all you need to do is go and get more exercise, it would be easy to see that as a brush-off, especially if it's done unsympathetically. The point is, if exercise doesn't feel like a positive step, it probably won't be one.
Harvey SB, Hotopf M, Overland S, & Mykletun A (2010). Physical activity and common mental disorders. The British journal of psychiatry : the journal of mental science, 197, 357-64 PMID: 21037212
