Does your neighbourhood cause schizophrenia?

The results of two new studies suggest that the neighbourhood you live in affects your chance of developing schizophrenia. Surprisingly, neighbourhood seems to have no effect on your risk of bipolar disorder.

The received wisdom says that schizophrenia affects 1% of the population worldwide, with little variation between race, country and area.

The trouble is, the received wisdom is wrong. We now know that the prevalence (total amount of cases) and incidence (amount of new cases per year) varies globally, nationally and locally.

These two new studies, led by Dr James Kirkbride, investigated whether street-by-street differences also have an effect.

The research team examined every person who was treated by mental health services in South East London for a first episode of psychosis over a two-year period.

Psychosis involves delusions and hallucinations and most often leads to a diagnosis of schizophrenia or bipolar disorder, bipolar being most associated with mood problems such as soaring highs followed by crashing lows.

South East London is notable for many things, not all of them positive. It’s a high poverty, high crime, highly urbanised inner-city area.

We know that one of the single largest environmental risk factors for schizophrenia is living in an urban area, and, unsurprisingly, this corner of the UK’s captial has one of the highest rates of psychosis in the world.

The team looked at all the areas, and, controlling for the effects of age, sex and ethnicity, used statistics to test whether any differences between areas were likely to due to chance, or whether they varied enough to be confident that the critical influence was the neighbourhood.

The map on the left shows the variation between neighbourhoods. If you know South East London, click on the map to see how it relates to specific areas.

You”ll notice that the toughest, poorest areas tend to have a higher rate of schizophrenia. In comparison, the rates for bipolar disorder were largely the same wherever the team looked.

Even if you don’t know the area at all, the amount of neighbourhood variation is quite startling. In some cases, moving just a few streets could dramatically affect your mental health.

In a second study, the team looked at characteristics of the area to try and see what risk was linked to.

Some main influences stood out: poverty, ethnic fragmentation, and, surprisingly, local election voter turnout.

In fact, a 1% increase in the number of voters in local elections was linked to a 5% reduction in new cases of schizophrenia.

Voter turnout itself is hardly likely to affect mental health, but the researchers suggest it might reflect the sense of community in the neighbourhood: the more you’re concerned about your neighbourhood the more likely you are to vote on issues affecting the area.

Ethnic fragmentation is a measure of how many people of your ethnic background live in your neighbourhood.

Immigrants are known to be at greater risk of schizophrenia than other people in the country, and South East London has a large immigrant population.

This might mean that contact with a community of people who share your cultural experiences may be protective against mental illness, perhaps again suggesting that ‘community spirit’ is key for mental health.

So why do all these things affect schizophrenia and not bipolar disorder? The researchers don’t discuss it in detail probably because it’s a bit puzzling.

The truth, of course, is just outside the front door.

Link to abstract of ‘Neighbourhood variation in the incidence of psychotic disorders in Southeast London’.

Link to abstract of ‘Neighbourhood-level effects on psychoses: re-examining the role of context’.

10 Comments

  1. Steve
    Posted July 6, 2007 at 1:10 am | Permalink

    Of course, those with schizophrenia (a debilitating illness) could just cluster in poor neighborhoods because of the nature of the illness. Your post and, I suspect, the article imply that neighborhoods cause schizophrenia. No “statistical” test could control for this possibility.

  2. Posted July 6, 2007 at 4:50 am | Permalink

    Except that bipolar disorder is a debilitating illness as well but the same clustering effect doesn’t seem to be happening so it likely isn’t just an issue of poverty. I agree that correlation doesn’t equal causation and there are certainly other factors at work. I don’t know how the mental health services work in that part of London but perhaps there is a difference in terms of availability of mental health services or even in terms of how the schizophrenic diagnosis is made?

  3. Posted July 6, 2007 at 8:48 am | Permalink

    In terms of diagnoses, all were made independently by the research team using a standarised interview and were found to be equivalent when checked. In terms of mental health services, the whole of the area is served by a single NHS trust (www.slam.nhs.uk) so there’s little variability in service availability.
    One area of difficulty is the analysis. The team used Bayesian statistics to allow for the fact that psychosis is a relatively rare disorder. Bayesian statistics require assumptions regarding risk, in other words, they need some estimates to start with. To get round this though, the team did four analyses, each with different assumptions and found broadly the same results (always schizophrenia varied, always bipolar did not).

  4. adriann
    Posted July 6, 2007 at 6:39 pm | Permalink

    The area may be serviced by a single agency that funds services, yet the individuals probably receive those services from smaller programs. They will “cluster” their clients around the program’s office/center to better reach them for meds, ADL assistance, therapy, and crisis prevention/intervention. I work with adults with schizophrenia & schizoaffective disorders who live in our group home and apartments in the community. None of my clients are able to drive and most cannot use public transportation due to their symptoms. They must rely on us or their own legs to get meds, attend appointments, obtain food & clothing, participate in activities, etc. Urban areas tend to provide more free resources, which my clients need, since most are unable to work and rely solely on SSI & SSD. We find them apartments when they are ready to leave the group home setting and visit them at least twice a day, so that plays a role in where they live. My clients come from many different locals and some are geniuses and some are borderline. The only thing I have found that they have in common is a history of either severe trauma (esp the females) or drug/alcohol addiction (mostly the males), a few have a genetic link. My adults are considered to be chronically impaired and some will never be able to ‚Äúgraduate‚Äù the program, so this does not reflect on those with mild schizophrenia. I really tried to make this short, I promise!

  5. Posted July 6, 2007 at 7:46 pm | Permalink

    The area covered by the study is about five miles across and about 7 miles top to bottom. Combining the populations of Southwark, Lambeth and Lewisham, it has a population of about three quarters of a million. There are few ‘less dense’ areas in this bit of London. For this reason, I suspect it’s unlikely that people cluster around particular offices as you’re always within walking distance of your local community mental health team.
    More importantly, the same point would apply that Romeo made above. If this is the case, it should equally apply to patients with bipolar disorder. Why does the incidence of schizophrenia vary but bipolar not?

  6. Posted July 7, 2007 at 2:20 am | Permalink

    Maybe people carrying subclinical assortment of bipolar genes are more wealthy, being more creative, and thus could provide more help to their sick “full-blown bipolar” relatives, so that they stay in rich neighbourhoods rather than sliding towards the poorer urbanized areas?
    And those bipolars who have no support – maybe they take their lives more readily compared to people with schizophrenia, instead of just moving to a poor neighbourhood, and so level off the statistics of distribution?

  7. john flournoy
    Posted July 7, 2007 at 5:10 am | Permalink

    Respectfully: It seems that it should be obvious to any scientist that there is absolutely no ground for concluding that “moving just a few streets could dramatically affect your mental health,” and I’m surprised to read such causation/correlation fallacies in this blog. One could actually do a study on whether movement of individuals from one area to another changed their chances of developing schizophrenia, I suppose, but this is really no where near that study — I don’t see this study taking into account how long these populations have resided in the area (please correct me if I’m wrong). At best this study seems to indicate environmental triggers for schizophrenia, or that there are subtle but important differences about the sort of ways schizophrenia and bi-polar disorder are debilitating.

  8. Posted July 7, 2007 at 8:43 am | Permalink

    Actually, I think “moving just a few streets could dramatically affect your mental health” is uncontroversial. The stress-vulnerability model of mental illness is widely (universally?) accepted. Some neighbourhoods are more stressful than others, so are more likely to lead to mental health problems. This is especially true in SE London, where you can move from a high crime, high violence neighbourhood to a relatively safe one in the space of a few streets.

  9. john flournoy
    Posted July 8, 2007 at 9:13 am | Permalink

    Right, the stress-vulnerability model is pretty uncontroversial. I posted without thinking, and, it seems, followed my own fallacious causative reasoning in assuming that the disease determines the geographical distribution. Pardon me.

  10. Posted July 8, 2007 at 11:43 am | Permalink

    These studies just further supports the idea that shared environment influences the onset of schizophrenia. I think that the diathesis-stress model is probably the best explanation… it suggests that there may be a genetical predisposition for schizophrenia and an environmental factor can trigger the disorder. It explains how neighbourhood can trigger schizophrenia (genetic predisposition in that the majority lives with their first-degree relatives for a long period of time after birth and therefore has a shared environment – neighbourhood).


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