Editor—Eaton et al report a strong risk relation between schizophrenia and coeliac disease.1 We do not believe that their data support this hypothesis.
They define their case sample as 7997 patients with schizophrenia, in whom they found four cases of coeliac disease. They then include the data on parents' coeliac status (eight cases) in their analysis, and this is potentially misleading. If the parents' data are excluded from the analysis the prevalence of coeliac disease in people with new onset schizophrenia is only 0.5 per 1000, which is the same as in their control group.
Eaton et al describe coeliac disease as rare in Denmark, which was the traditional view. Their sample population dated from 1981-98, when diagnostic testing for coeliac disease advanced. Recent data using endomysial antibody to screen the Danish population suggests a prevalence of 1 in 400, more akin to neighbouring Scandinavian countries.2 Underascertainment of the true prevalence of coeliac disease is therefore a real possibility and a potential confounding factor.
Competing interests: None declared.
References
- 1.Eaton W, Mortensen PB, Agerbo E, Byrne M, Mors O, Ewald H. Coeliac disease and schizophrenia: population based case control study with linkage of Danish national registers. BMJ 2004;328: 438-9. (21 February.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Weile I, Grodzinsky E, Skogh T, Jordal R, Cavell B, Krasilnikoff PA. High prevalence rates of adult silent coeliac disease, as seen in Sweden, must be expected in Denmark. APMIS 2001;109: 745-50. [DOI] [PubMed] [Google Scholar]