On the high prevalence of mental disorders

There are a very large number of different mental disorders, at least according to the recent American Psychiatric Association diagnostic classification. More to the point of this blog, certain mental disorders are also extremely common – in particular, depression.

A recent study compared exercise treatments with anti-depressants or cognitive behaviour therapy in a meta-analysis of head-to-head trials.[1] Each of these modalities has been shown to be better than nothing, but they appear to be of similar effectiveness.

What are we to make of this? Presumably, people should be given the choice. Also, the dose of the medication is reasonably well standardised. That of exercise is very variable. I am training for the world’s largest bike race (the Cape Argus Cycle Tour) and have been doing a lot of exercise at the limits of my endurance. This has a euphoric effect, which was probably not replicated for the average person in the trials. Exercise also has other health benefits, apart from the mind.[2]

But what if we stand back from these rather instrumental results, and consider the matter from a more anthropological perspective? The really interesting thing at this distance is the observation that mental illness is so extraordinarily common and depression affects approximately a quarter of all human beings at some point in their life.[3] Of course, the 25% incidence threshold is a choice – society could use a higher or lower cut off if it wished. Nonetheless 25% of people endure one or more extended periods where their answers on a pro forma indicate that they feel pretty miserable.

This invites the question as to why such a feeling is so common. There seem to be two possible aetiologies for this phenomenon. Firstly, it may be the case that being a human being is very hard, irrespective of the society or time in which one dwells. Alternatively, living in a modern market economy, for all the comforts it gives us, may be particularly psycho-toxic. I think this question is near unanswerable. However, I offer the hypothesis that some societies offer their citizens greater opportunities than others, but these opportunities come at a price. This price is exacted because opportunity entails the risk of failure. The United States, at the moment, is a wonderful habitat for the liberal cognitive elite, sitting in Boston, Chicago or Palo Alto, but the meritocracy has a down side. It seems plausible that people brought up to have no great aspirations, perhaps in a communist or feudal world, might be at lower risk of depression than those exposed to competition with their peers. I would be very grateful if anyone can supply some empirical evidence on this point, though I suspect the results will always be contestable. My observation is that people will always tend to migrate from less free to freer societies, even though they are not so poorly informed as to think that this will necessarily take them to the top. It is hope that projects them into the liberal maelstrom. Like Candide,[4] I would certainly make such a trade-off.

All this reminds me of an article in the Times Higher written by the Vice-Chancellor of the University of Buckingham (Prof Terence Kealey), which likened people in a competitive society to a herd of wildebeest – yes, the gnu of the African plain. Male wildebeest compete to become the alpha male. They try hard, and then most eventually fail. At some point, survival of the herd is dependent upon the contest ending with the unambiguous emergence of the leader. At that point, the unsuccessful bulls become subdued; they lower their heads and graze quietly while the Vice-Chancellor among the gnu procreates to his heart’s content. Biochemically, the cerebral serotonin metabolism of the remaining herd has been altered – in short, they are depressed. But hey, they had their chance.

So let’s get back to treatment. Whether because our society is meritocratic or because it is just part of the human condition, many people will cross the threshold of clinical depression. If they do, they can be given the choice between exercise, anti-depressant drugs, or talking therapy. They can try one, and then switch to the other, although I suspect that cognitive behavioural therapy is by some margin the most expensive and might have to be rationed for that reason. I mean, if a quarter of the population get depressed, it would take a mighty big mental health workforce to provide behavioural therapy for all of them. As for prevention, even if the human condition is such that many people will warrant the label depression, it may be worth trying to mitigate the problem through public health means, such as tackling bullying in schools and targeting high risk groups, such as children who have recently been in care. Finding out whether or not these measures are effective is an aim of the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) for West Midlands.

–Richard Lilford


[1] Cooney GM, Dwan K, Greig CA, et al. Exercise for depression. Cochrane Database Sys Rev. 2013; 9: CD004366.

[2] Larson EB, Bruce RA. Health Benefits of Exercise in an Aging Society. Arch Intern Med. 1987; 147(2):353-6.

[3] WebMD. Depression Health Center. Available at: http://www.webmd.com/depression/guide/major-depression. 2013 [accessed 17 Dec 2013].

[4] Voltaire. Candide, ou l’Optimisme. Available at: http://www.gutenberg.org/ebooks/19942. 1759 [accessed 18 Dec 2013].


2 thoughts on “On the high prevalence of mental disorders”

  1. Richard describes beautifully the social competition theory of depression. This argues that depression is an evolutionary adaptive mechanism to maintain social cohesion and purpose. ‘Down-ranking’ and subordination to dominants is associated with the phenomenology of dysphoria in homo-saps, but the behaviours and social signals remain the same (see 1 ). It is no accident that social inequalities and societal barriers to social status and attractiveness are the best predictors of depression and, come to think of it, psychosis! Shame is an interesting emotion with a similar pedigree: it functions to challenge the status and power of the dominant. I suppose this is the stock-in-trade of the red-top news media?
    Our CLAHRC-WM mental health theme has used this framework in psychosis; for example, to understand the subordinate relationship between voice hearer and voice, which can motivate the need to comply with voices’ extreme commands(2).

    1. Leon Sloman and Paul Gilbert. Subordination and Defeat: An Evolutionary Approach To Mood Disorders and Their Therapy. Routledge.
    2. Birchwood, M., Emmanuelle P, Tarrier,N., Dunn, G., Lewis, S., Wykes,T., Davies,L.,Helen Lester, H., and Michail, M. “A Multi-Centre, Randomised Controlled Trial of Cognitive Therapy to Prevent Harmful Compliance with Command Hallucinations.” BMC Psychiatry 11, (2011)

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