The association between atopic disorders and depression

The Northern Finland 1966 Birth Cohort Study

Markku Timonen

Department of Psychiatry, Oulu University Hospital
Department of Public Health Science and General Practice, University of Oulu

Abstract

An excess of atopic allergies has been found in patients with depression, and conversely, increased amounts of depressive symptoms have been reported in patients with atopic disorders. Thus far, however, the findings have mainly been based on clinical samples. In this thesis, the association between atopic disorders and depression was investigated at epidemiological level by using data from the Northern Finland 1966 Birth Cohort.

An unselected cohort of 12058 liveborn children was followed prospectively from prenatal stages until 1997. During the 31-year follow-up, 6025 cohort members underwent skin prick tests. Data on lifetime depression diagnoses and atopic conditions were obtained from postal questionnaires and Finnish Hospital Discharge Registers, and the severity of the depressive symptoms was assessed with Hopkins Symptom Checklist-25. Information on the family histories of the atopic disorders was obtained from questionnaires of the 31-year follow-up.

Females with positive skin prick test responses and self-reported histories of allergic symptoms exhibited a 2.7-fold probability of developing lifetime depression. The corresponding probability increased in line with the increased severity of depressive symptoms in atopic but not in non-atopic females, ranging from 3.0 to 4.7-fold. Among males, the atopy-depression association was seen only in the highest depression scores, the odds ratio being up to 6.3-fold. While the most severe, hospital-treated manifestations of both disorders were considered, atopic disorders increased the risk of depression 3-fold independently of the subject"s gender and sociodemographic characteristics. When investigating the effect of familial atopy on a child"s depression, maternal atopy increased the probability of lifetime depression nearly 2-fold in females, and over 4-fold, when a female cohort member"s own atopy was also present.

At epidemiological level, the presence of atopic conditions seemed to increase the probability of lifetime depression especially in females. Since both atopic disorders and depression are illnesses of major public health importance in Western countries, also the co-morbidity between these disorders should be seriously taken into account in clinical practice. Further investigations are called for in evaluating whether this association is specific to atopic disorders, since increased risks of depression have been noted in connection with many other physical diseases as well.

Table of Contents
Acknowledgements
Abbreviations
List of original publications
1. Introduction
2. Review of the literature
2.1. Definition of atopy
2.2. Etiological factors of atopic disorders
2.3. Asthma bronchiale, atopic dermatitis, allergic rhinitis, and allergic conjunctivitis
2.3.1. Asthma bronchiale
2.3.2. Atopic dermatitis (AD)
2.3.3. Allergic rhinitis and allergic conjunctivitis
2.4. Trends in the occurrence of atopic disorders
2.5. Some biological aspects of atopic disorders
2.5.1. Regulation of immunity
2.5.2. Immediate hypersensitivity
2.5.3. Allergen-specific T-cell memory
2.6. Definition of depression
2.7. Prevalence of depression
2.8. Etiological factors and biological aspects of depressive disorders
2.8.1. Some biological aspect of depression
2.8.2. Immunological alterations in depression
2.9. Earlier studies concerning the association between atopic disorders and depression
2.9.1. Allergic symptoms in patients with depression
2.9.2. Depression in patients with atopic disorders
2.9.3. Other studies concerning atopy-depression association
2.9.4. Genetic studies
2.9.5. Other factors related to atopy-depression association
2.10. The associations between other physical disorders and depression
2.11. Summary of the reviewed literature: what is known and what should be studied?
3. Aims of the present study
4. Materials and Methods
4.1. The Northern Finland 1966 Birth Cohort
4.1.1. Data collection
4.1.2. The follow-ups
4.2. Variables
4.2.1. Outcome variables
4.2.2. Exposure variables
4.2.3. Confounding variables
4.3. Statistical methods
4.4. Ethical considerations
5. Results
5.1. Atopy and self-reported lifetime depression
5.2. Atopy and the severity of current depression verified by HSCL-depression subscale
5.3. Hospital-treated atopic disorders and depression
5.4. Atopy of the first degree relatives and depression of the proband
6. Discussion
6.1. Overview of the results
6.2. Discussion of the results
6.2.1. The association between atopy and depression
6.2.2. Gender difference and severity of depressive symptoms
6.2.3. Atopy in first degree relatives of depressed probands
6.2.4. Regular daily smoking and living in a city
6.3. Theoretical considerations
6.3.1. Biological explanations
6.3.2. Psychosocial explanations
6.4. Methodological considerations
6.4.1. Strengths of the study
6.4.2. Limitations of the study
7. Conclusions
7.1. Main conclusions of the results
7.2. Research implications
7.3. Clinical implications
References
List of Tables
1. Confounding variables used in the original publications (I–IV)
2. Associations between prick tested atopies and self-administered information of doctor-diagnosed lifetime depression in the Northern Finland 1966 Birth Cohort. (II: Table 1).
3. The associations between self-reported doctor-diagnosed lifetime depression and atopic symptoms, verified by skin prick tests as assessed with three logistic regression models according to different cut-off points for HCSL-25 depression subscale (13-items) scores after adjusting for confounding variables* in the Northern Finland 1966 Birth Cohort by gender (III: Table 2).
4. The association between hospital-treated atopic disorders and hospital-treated depression among the Northern Finland 1966 Birth Cohort members and their sociodemographic factors (I: Table 1).
5. Risk of depression associated with family atopy variables and with a cohort member’s own atopy for males and females in the Northern Finland 1966 Birth Cohort (IV: Table 2).
List of Figures
1. Differentiation into Th1 or Th2 subsets from naive Th0 cells and corresponding cytokine patterns and effector mechanisms. Modified from the illustration of Elenkov & Chrousos (1999).
2. The flowchart of the data collection procedure in the Northern Finland 1966 Birth Cohort Study and the main data used in the original publications I–IV.
3. CHAID flowchart of the statistically significant predictors for self-reported lifetime depression involving female cohort members, the Northern Finland 1966 Birth Cohort study (IV: Figure 1).
4. CHAID flowchart of the statistically significant predictors for hospital-treated depression involving female cohort members, the Northern Finland 1966 Birth Cohort study (IV: Figure 2).
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