Introduction

It has been known for over a century that abnormalities of glucose metabolism are more common in those suffering from certainforms of mental illness (Kasanin, 1926), but only in the pastfew years has there been any serious attempt to establish the exact nature of the association. We are now in a situationwhere a great deal of data and opinions have surfaced in ashort space of time. In order to bring this body of data intoa single forum to debate its significance and – moreimportantly – to examine how it should influence practice,it was felt appropriate to convene a consensus meeting on diabetesand schizophrenia. The aims of the meeting were to bring agroup of interested and informed clinicians and pharmacologiststogether to present and debate all the currently availabledata, opinions and practices from around the world that relateto the association between schizophrenia and glucose abnormalities.In order to do this we felt it crucial to involve experts notonly in psychiatry but also in diabetology. One of the majorroles of the convened group was to give some sort of hierarchicalbasis to the many types of data that have been published. Theprime focus of the group was to agree a consensus statement that would give practising psychiatrists and diabetologistsa clear message as to the current state of knowledge, beliefsand potential best practices.

The group identified many areas of debate and disagreement within psychiatry and medicine, and in particular recognised thatit is not a universal belief in the UK in 2003 that psychiatristsshould indeed be responsible for the physical health of theirpatients. The aims of the group therefore were to produce apragmatic and sensible consensus statement, which could beconsidered for use throughout the UK and Ireland. Most of the recommendations are evidence-based, but in areas where thereis a lack of evidence a consensus opinion was formed. Sinceit is clear that we do not have answers to all of the questions,one of the main conclusions of the group was that large, prospective,long-term studies are urgently required.

Why has a consensus statement not been produced before? Theanswer to this question is probably that the data simply havenot been available until now (Mohan et al, 1999). Dora Kohenpoints out that the issue has been the subject of much previous debate but such debate has not led to a conclusive outcome.Dixon et al (2000) showed clearly from the Patient OutcomesResearch Team database that not only diabetes but very manyother physical illnesses are undiagnosed in many of our patients.

UNDIAGNOSED DISEASE

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UNDIAGNOSED DISEASE

A vast amount of new data pertaining to glycaemia and schizophreniahas been generated in the past few years. Most of the datahave been published in the psychiatric literature, and thereis little evidence that physicians and diabetologists haveconsidered this to be an important area for their own research.Yet the diabetic literature is unanimous in the view that throughout the world there are huge numbers of people with undiagnoseddiabetes and impaired glucose tolerance (Jonsson, 2002). Thesepatients go undiagnosed primarily because diabetes is oftenan asymptomatic illness, and even if symptoms are present theyare rarely unique and obvious enough to lead to an early diagnosis.This issue is examined in detail by Richard Holt in his reviewof the epidemiology and the current approach to diagnosis indiabetes mellitus (Holt, 2004, this supplement). He stressesthe costly individual, social and economic consequences of the problem.

Within this cohort of people with undiagnosed glucose disorderis a significantly large group of individuals with psychiatricillness. There seems to have been an absence of awareness untilrecently that schizophrenia (and possibly bipolar disorderas well) could be considered as an independent risk factorfor the development of diabetes (Ryan & Thakore, 2002).A recent BMJ series on all aspects of diabetes (epidemiology, diagnosis, management and complications) was notable for itsabsence of any mention of schizophrenia. Here indeed is a hugepotential cohort of people with diabetes, and Bushe & Holt (2004, this supplement) stress the value of early diagnosisand treatment, which might lead to a reduction in the all-too-commondeaths from cardiovascular events. We know that natural causesand not suicide explain the majority of the excess mortalityassociated with schizophrenia (Harris & Barraclough, 1998;Brown et al, 2000). We also know that diabetes is best considereda ‘vascular illness’, for which most patients routinelyreceive statins, angiotensin-converting enzyme inhibitors andaspirin in addition to their hypoglycaemic treatments. Furthermore,there appears to be reasonable evidence that diabetes can beprevented if those at greatest risk are targeted early enoughand comply with their treatments (Knowler et al, 2002).

HIERARCHICAL ASSESSMENT OF THE DATA

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HIERARCHICAL ASSESSMENT OF THE...

One of the most important tasks undertaken by the consensusgroup was to attempt to classify the many different types ofdata published and presented on a hierarchical basis. Mostdata reviewed had been generated from retrospective epidemiologicalstudies which provided incidence and/or prevalence data fordiabetes (Cavazzoni et al, 2004, this supplement). It is importantto note that none of these studies gave incidence data relatingto impaired glucose tolerance, and none of them specified howmany (if any) individuals in each population had been activelyscreened for abnormal blood glucose levels. Many of these retrospectivestudies were sponsored by pharmaceutical companies, and mostgive confusingly different results using essentially the samecohort of patients.

The prospective data examining the relationship between schizophreniaand diabetes began to emerge in 2003, and most of the datacurrently in the public domain have not yet undergone peerreview. This body of data is reviewed by Bushe & Leonard(2004, this supplement), who conclude that the associationbetween schizophrenia, antipsychotic medication and diabetesis largely based on less than optimal retrospective studies.The latter studies are reviewed in the paper by Haddad (2004,this supplement). A few studies have included a placebo group,and through these studies it emerges that we cannot necessarilyblame antipsychotic medication when diabetes develops in anindividual with schizophrenia. In the prospective studies that included both a placebo group and a requirement to activelyand regularly measure blood glucose levels (as in randomisedcontrolled trials performed to US Food and Drug Administrationstandards), we have learnt that the incidence of newly diagnoseddiabetes does not appear to differ greatly between placebo groupsand groups in which active drug comparators have been used.

HOW DOES SCHIZOPHRENIA PREDISPOSE TO DIABETES?

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HOW DOES SCHIZOPHRENIA...

Jogin Thakore reviews his own studies exploring the link betweenvisceral obesity and impaired fasting glycaemia in drugnaïvepatients with schizophrenia (Thakore, 2004, this supplement).He suggests that schizophrenia is independently associated witha range of metabolic disturbance. In my own article (Dinan, 2004,this supplement) I link this disturbance to the stressexperienced by patients with schizophrenia and the consequentactivation of both the hypothalamic–pituitary–adrenalaxis and sympatho-adrenal medullary system, while Malcolm Peetexamines the association with diet (Peet, 2004, this supplement).

ANSWERING THE DIFFICULT QUESTIONS

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ANSWERING THE DIFFICULT...

Our consensus meeting considered data in all formats –journals, posters and data available from recent presentationsat international congresses. In short, we attempted to haveavailable for review all data that were in the public domainin October 2003. We do not pretend that our group has all theanswers, but we hope that at least we might have asked all the questions. What you will find in this supplement is a reviewof all the data that exist at present to help us answer themost difficult questions relating to diabetes, schizophreniaand antipsychotic medication. The consensus document shouldbest be viewed as a working tool that will allow future best practice to emerge and be tested.

There is little doubt that some psychiatrists feel challengedby non-psychiatric illness and will feel threatened by beingasked to screen for a physical illness such as diabetes. However,in their review Gough & Peveler (2004, this supplement) give pragmatic solutions for intervention in patients withschizophrenia. Overall, we have tried in this supplement togive suggestions, rather than be too prescriptive about theservices individual psychiatrists might provide and the rolesthey might choose to adopt. There may be merit in reconveningthe group in the months and years ahead as more data emerge.

REFERENCES

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