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Holy Sacred Cow! Why Reactions to the Exercise and Depression Trial Go to the Heart of Scientific Controversy

The views expressed are those of the author and are not necessarily those of Scientific American.


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Drawing by Hilda Bastian.

Drawing by Hilda Bastian.

What do you believe about the effects of exercise and depression – and why do you believe it? Are you personally unenthusiastic about exercising, or are you closer to religious fervor about it?

These are critical questions. Because it doesn’t matter how much you believe in the importance of science. If you have a very strong prior existing belief, chances are it’s going to exert a strong bias on how you select and react to evidence on the subject.

In the ideal rational world with loads of expertise and time on your hands, that wouldn’t matter when you came across research. If you were interested in the issue, you would carefully assess the biases and strengths of new research, with an equally careful assessment of the existing body of research. You wouldn’t make up your mind about the current state of knowledge till after this systematic assessment was done.

But that’s not what it’s like, is it? In the real world, what we already believe often determines whether we even read something at all. And if it reinforces our belief – “Ha! See? I knew it! More proof!” – we might whizz off an email or a tweet without more than a brief skim of the abstract (or even less).

But if research challenges beliefs we hold dear, we might tear the challenging article to pieces. We tend to look for methodological weaknesses in a way that we don’t do if we agree with conclusions.

This selective skepticism is how we deal with a world of too much information and the confusion it could keep us in. But it can lead us badly astray. It’s one of the ways that sacred cows get to be sacred cows: not looking too closely at welcome news and energetically discounting inconveniently disquieting results. When results inconveniently emerge that challenge orthodoxy, scientific controversy is inevitable.

Exercise and depression is a particularly tough one when it comes to bias. There’s such profound confounding here – a classic case of “what comes first, the chicken or the egg?” Does your depression ease because you start exercising – or can you get out and exercise more because your depression is less crippling? And you can’t blind people to whether or not they’re exercising of course, so that affects self-rating. It’s not surprising then, that high quality systematic reviews on the subject bemoan how little research of minimal bias exists.

What about the “several meta-analyses” cited by Scicurious in this week’s blog post? Well, one wasn’t a meta-analysis at all: and it wasn’t a systematic review either. Nor did it take into account the biases of the primary research it was considering. The other was a systematic review and meta-analysis – but it wasn’t of trials directly assessing the impact of exercise in people diagnosed with depression.

Consider the three recent enough, good quality systematic reviews I could find on the direct question (Krogh, Mead, NICE). When raising the bar to include only the most unbiased research, we’re left with a very small body of evidence that suggests maybe a little short-term benefit. No real increase in recovery rates or speed of recovery from clinical depression has been shown. A good quality big trial of long-term sustained exercising could push this either way.

What about Scicurious’ critique of the trial that started the reactions? Well, she’s right to say this trial wasn’t seeking to address the efficacy of exercise. But much of the methodology she’s criticizing is good practice in a randomized controlled trial – like the reliance on standard intention-to-treat analysis (“Not only that, the study did not discount those who did not exercise”). This trial, as Scicurious rightly points out, was meant to test the effectiveness of the encouragement to exercise, not exercise itself. As both the paper and its much-maligned press release made abundantly clear (although the title might have confused the issue).

Is this a perfect trial? No, there’s no such thing. But it’s a very good one. And it’s addressing a critical question, because we need to know what the best advice and support to offer people could be. Truth is, we don’t know how efficacious exercise really is. That matters, partly because anything that can have a positive effect could also have a negative one. If we exercise and feel better we can take credit for our recovery. But if we don’t exercise, will we blame ourselves for still feeling so bad?

Hilda Bastian About the Author: Hilda Bastian likes thinking about bias, uncertainty and how we come to know all sorts of thing. Her day job is making clinical effectiveness research accessible. And she explores the limitless comedic potential of clinical epidemiology at her cartoon blog, Statistically Funny. Follow on Twitter @hildabast.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 8 Comments

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  1. 1. promytius 7:02 pm 06/13/2012

    Which came first, the depression or the long walk?

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  2. 2. What4 10:31 pm 06/13/2012

    How about comparing drug treatment for depression with holistic treatments, such as combining exercise with a strict healthy diet, deep relaxation, meditation, gardening, reestablishment of sleep-and-waking patterns, social contacts, taking care of a pet dog, acting in amateur theater, regular watching of laugh-out-loud comedies, and the like?

    Life is too complicated for most of us for a change in one variable to improve such a complex factor as depression — but many small changes can have a major effect.

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  3. 3. way2ec 11:25 pm 06/13/2012

    Add to the mix that depression, as in major clinical depression, can just about wipe out bias and or the ability to be objective about most anything. Is the glass half full or half empty? And the answer is “Who cares?” When “just” getting out of bed is problematic, all the rest seems like light years away in an unimaginable future. The thought that someone would design a test where a large group of depressed people would have only the exercise variable tested and both the “control” group as well as those getting the exercise would get no other treatments, thus “controlling” only for exercise, seems cruel, although “scientifically” the only way to test for exercise benefits. And what of the “placebo” effect, “forced” to exercise vs. “encouraged” and helped to exercise, where the TLC might be the difference in both benefits and sense of well being. I like What4′s approach but personally, give me ALL of the above, the medications AND the holistic treatments, anything and everything to help me get out of the dark cold empty pit of depression and back into the light with the rest of the living. (I even moved out of the NW and now live in Mexico; sunlight? warmth? new language? different culture? all of the above!)

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  4. 4. gdn 11:54 pm 06/13/2012

    Depression is a complex phenomenon and his inherently linked to your genetic makeup and family environment (past and current), but healthy life style certainly helps in reducing the risk. The best way to counter depression is a two step process and it will work in most of the cases:
    1. Do the right action always or atleast make a genuine effort- this is only possible if you always thank the lord for what you are and what you have, and if you have to compare yourself do it with persons who are less fortunates.
    2. Accept the outcome graciously and thank the almighty. It is called Postive Outlook under all circumstances.
    The above must be done regularly (Introspection and Retrospection). The above process helps in controlling your mind.
    The word D will disappear from your dictionary (in most of the cases).

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  5. 5. curmudgeon 7:48 am 06/14/2012

    Ah gdn. The glib, the trivialising and the frankly bonkers all in one message! Anyone capable of ‘a positive outlook’, ‘accepting outcomes graciously’ simply does not have depression! It’s not bad enough that we’re staring up from the bottom of a deep dark, there’s some idiot at the top telling us that all we’ve got to do is ‘believe’ and we’ll leap out of there in a single bound!

    There is no comparison with people ‘less fortunate’ because it’s impossible to believe that any such people exist. And what in the name of God is the ‘right action’in the midst of a depression, when the ‘only’ thing, let alone the ‘right’ thing, to do (or so your brain tells you) is to jump off a bridge to end your relationship with a world that hates you?

    If only ‘happy’ people would take a good look at themselves and realise the damage they are doing with their sage advice! Job’s comforters all!

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  6. 6. curmudgeon 8:03 am 06/14/2012

    Would it not be helpful to have a definitive study of the effect of exercise on serotonin levels rather than depending on what is essentially no more than anecdotal evidence? After all the derangements of depression (at least when it’s not at it’s genuinely suicidal worst) include an inability to accurately judge your mood and a tendency to lie to yourself and others about it anyway.

    As it is, I’m inclined to believe the negative results of this latest study because of the well known variation of Morton’s Law (rats, when experimented on, develop cancer) that shows that depressives when taken seriously and given attention (such as being monitored by ‘scientists’) tend to improve. If the lack of positive correlation persists over and above this effect then it really does suggest that we should take it seriously!

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  7. 7. portland17 6:12 pm 06/14/2012

    It would be nice if the same standards the author applies to exercise would be applied to antidepressants. When it has been (see Irving Kirch’s work), the results are very similar.

    The truth is, nobody really knows what’s happening when a person is depressed, and there is no one approach that helps everyone. I would guess that for some folks, exercise is just the thing, even if they have to drag themselves out of bed to do it, and for others, they either can’t make it work or it doesn’t help at all.

    As a person who recovered from extreme anxiety and depression, I can say that it has been a long process and that multiple approaches and modes of treatment were necessary. Environmental factors, motivation, relationships, family history and trauma, employment, sleep issues, poverty, societal oppression, all come into play. It’s silly to think that simply exercising will make everything all better, but it certainly can be a factor in a recovery plan. My experience as a sufferer and as a mental health professional says that the most important factor is engaging the sufferer in the process of designing a recovery plan, and supporting this process over time. Putting the locus of control outside the client, whether with drugs, prescribed exercise, homeopathics or whatever, is ultimately self-defeating. The real path to recovery is the depressed person finding a way to increase his/her own sense of control over his/her life, in whatever way works for that client. There is no panacea, natural or otherwise. Beating depression is hard work.

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  8. 8. jh443 2:43 am 06/15/2012

    Having personally recently started on the road to recovery from MDD after almost 30 years, I can state that in my case the #1 obstacle that kept me there for so long was “perception.” I perceived the negative aspects of life as being more realistic than any of the positives.

    Worse yet, even the “positives” were viewed in a negative light. Trying to “count my blessings” was an exercise in futility – all it would accomplish was a reminder of the disadvantages that these so called “blessings” had brought.

    I can see now just how twisted my point of view was, and I am grateful that I’ve progressed to the point where I can no longer even comprehend it. What this fact does prove to me, though, is that if I – who has “been there” – can no longer understand it, then someone who has never experienced it has no hope of understanding it in the least.

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