Prevalence and risk of atopic disorders among schizophrenia patients: A nationwide population based study

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Abstract

Objective

Although a body of evidence indicates a link between psychiatric illnesses and allergies, no one has investigated the association between schizophrenia and atopic disorders. The objective of this nationwide population-based study was to examine the prevalence and risk of atopic disorders (asthma, allergic rhinitis, urticaria, and atopic dermatitis) among schizophrenia patients.

Method

This study used data from the Taiwan National Health Insurance Research Database covering the years 2000 to 2002. A total of 44,187 patients diagnosed with schizophrenia in the year 2000 were included, together with 132,561 matched non-psychiatric controls. Follow up until the end of 2002 identified concurrent diagnoses of atopic disorders. Logistic regression analyses were performed after controlling for the covariates of socio-demographic characteristics.

Results

Findings indicated high comorbidity, with 20.2% of schizophrenia patients (approximately one in five) experiencing concurrent atopic disorders. Moreover, schizophrenia in patients was independently associated with a 1.3-fold increased risk (95%CI = 1.24–1.39) of concurrent asthma, after adjusting for socio-demographic characteristics. Yet the risk of diagnosed allergic rhinitis and urticaria was 23% (95%CI = 0.74–0.81) and 26% (95%CI = 0.72–0.77) lower, respectively, among schizophrenia patients compared to people without any psychiatric disease.

Conclusion

Data suggests an increased risk of asthma and decreased risk of allergic rhinitis and urticaria among schizophrenia patients. Future studies on the identification of common etiologic pathways for schizophrenia and asthma could be significant for developing innovative treatments that target both illnesses concurrently.

Introduction

Schizophrenia is a chronic psychiatric illness with an approximate prevalence of 1% worldwide (Freedman, 2003). A number of studies have demonstrated an excess of mortality among schizophrenia patients, with overall standardized mortality ratios of schizophrenic to general populations ranging approximately from 1.5 to 4.5 (Capasso et al., 2008, Wood et al., 1985). Despite the fact that increased mortality among schizophrenia patients resulted from higher prevalence of physical disease, the somatic wellbeing of such patients has been neglected for decades (Leucht et al., 2007). Physical comorbidities should be a serious concern both scientifically and for effective clinical management of schizophrenia. A review of literature on the co-occurrence of physical illnesses and schizophrenia shows that areas including atopic disorders have not been sufficiently considered.

Globally, the prevalence of atopic disorders, a familial group of allergic disorders including asthma, allergic rhinitis, urticaria, and atopic dermatitis, has continued to rise in the past few decades (Asher et al., 2006). In developed countries like Taiwan, as many as one in three or four individuals suffer from certain atopic disorders (Asher et al., 2006, Liao et al., 2005). Previous studies have investigated the co-occurrence of psychosocial factors and allergies, proposing a bidirectional relationship. Physiological, behavioral, and socioeconomic factors have all been proposed as playing a role in the reciprocal association between psychiatric symptoms and atopic disorders (Chida et al., 2008). Specifically, stress or psychiatric illness might elicit factors (e.g., inflammatory processes, poor diet, sleep disturbance, unhygienic living environment, and poor medical compliance) that would intensify atopic diseases. Conversely, atopic diseases negatively affect mental health through chronically distressing symptoms, consistently unsuccessful treatment with cumulating medical expenses, and impaired social functioning (Chida et al., 2008, Marshall and Roy, 2007).

Although a body of evidence indicates that allergies are associated with psychosocial factors, most studies have centered on psychiatric disorders such as anxiety disorders, depressive disorders, and attention deficit hyperactivity disorder (Patten and Williams, 2007, Slattery, 2005). To our knowledge, none has investigated the association between schizophrenia and allergies. Since atopic disorders are common and distressing, significantly disrupting social, personal, and domestic life, there is a substantial and immediate need to address allergies among schizophrenia patients.

The objective of this nationwide population-based study was to document the prevalence and risk of atopic disorders among schizophrenia patients. Schizophrenia patients who visited outpatient departments at any time in the year 2000 were followed up till the end of 2002 to identify the extent of comorbid atopic disorders including asthma, allergic rhinitis, urticaria, and atopic dermatitis. Risks for schizophrenics are compared with non-psychiatric matched controls.

Section snippets

Database

This study used 2000–2002 data from the Taiwan National Health Insurance Research Database (NHIRD). Taiwan implemented a National Health Insurance (NHI) program in March 1995 that is characterized by mandatory enrollment in a government-run, single-payer insurance system, and comprehensive benefits coverage. The program currently has over 21 million enrollees, representing around 97% of the island's population. Therefore, the NHRID is one of the largest and most comprehensive nationwide

Statistical analysis

The SAS statistical package (SAS System for Windows, Version 8.2) was used to perform the statistical analyses. Chi-square tests were used to examine demographic differences between the two cohorts. Demographic characteristics included age, gender, urbanization and geographical region (Northern, Central, Eastern and Southern Taiwan) as well as monthly income (0, NT$1–NT$15,840, NT$15,841–NT$25,000, ≥ NT$25,001 (NT = New Taiwan Dollar, with an exchange rate in the year 2000 of 1 USD = 31.2 NT)).

Results

Table 1 describes the demographic distributions for the two cohorts. The χ2 tests show significant differences in monthly income (p < 0.001), urbanization level (p < 0.001) and geographic region (p < 0.001) between these two cohorts. Compared to the comparison cohort, schizophrenia patients were more likely to have lower monthly incomes, to reside in the most urbanized areas and in the central and southern parts of Taiwan.

The distribution of atopic disorders for the two cohorts is provided in Table 2

Discussion

To our knowledge, this is the first report on the prevalence and risk of atopic disorders among schizophrenia patients. Results indicate a considerably higher comorbidity of schizophrenia and allergies, with 20.2% of schizophrenia patients (approximately one in five) concurrently having atopic disorders. Moreover, schizophrenia in patients was independently associated with a 1.3-fold increased risk of asthma, after adjusting for sociodemographic characteristics. Yet, their risk of diagnosed

Role of funding source

None.

Contributors

Dr. Chen and Dr. Lin designed the study and wrote the draft. Dr. Lee managed the literature search and analyses. Dr. Lin undertook the statistical analyses. All authors contributed to and approved the final manuscript.

Conflict of interest

None.

Acknowledgements

This study is based in part on data from the National Health Insurance Research Database provided by Taiwan's Bureau of National Health Insurance, Department of Health and managed by the National Health Research Institutes. The interpretations and conclusions contained herein do not represent those of the Bureau of National Health Insurance or the National Health Research Institutes.

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