The association betweenself-reported eczema and common mental disorders in the general population: The Hordaland Health Study(HUSK)
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Background and objectives The field of psychodermatology addresses the interaction between skin and mind, and it has been speculated that the shared embryological origin of the central nervous system (CNS) and the skin from the primitive neuroectoderm could explain the communication between the two systems. The association between anxiety, depression, and eczema is well established, but factors underlying this association remain unclear. There are several reports of a link between psychological stress and the onset or exacerbation of skin disorders, but psychodermatology has primarily focused on depression and anxiety in eczema, whereas the contribution of other psychological factors hardly has been studied. Eczema sometimes follows a long-lasting and relapsing course which could lead to reduced ability to work and subsequent sick leave. However, the association between eczema and sick leave is only partially supported in the literature. The present thesis is based on four papers, all with the emphasis on eczema in relation to mental health (first with emphasis on anxiety and depression, later also with a focus on somatization). The aim of the first paper was to examine the hypothesized association between anxiety/depression and IgE, in a female sub-population in HUSK. The aim of the second paper was to examine the empirical relevance of proposed contributing factors for the association between anxiety, depression, and eczema. These proposed contributing factors included omega-3 fatty acid supplement, female gender, health anxiety and somatization. The aim of the third paper was to test the hypothesis that eczema is an independent and unconfounded risk factor for long term sick leave; and to compare the risk for long term sick leave following eczema with the risk following asthma and allergic rhinitis, which both are prevalent conditions in the general population, and constitute, together with atopic eczema, the “atopic triad”. We also explored possible confounding or mediating factors in this hypothesized association. The aim of the fourth paper was to explore the association between somatization and eczema by examining the extent of somatization in eczema compared to allergic rhinitis, and to examine if eczema was more strongly associated with somatization than anxiety and depression. Finally, we examined the relationship between the site of eczema and somatization for individual somatic symptoms and for somatic symptoms as a whole. Methods In all four papers, we employed cross-sectional data from a large population-based study, the Hordaland Health Study (HUSK) which was carried out from October 1997 until June 1999, in western Norway. In the first paper, a sub-sample of 374 female participants was screened for serum IgE levels, and in the other three studies about 15000 individuals from the general population were included, measuring several self-reported health factors. Anxiety and depression was measured using the Hospital Anxiety and Depression Scale (HADS). Information on eczema, asthma, allergic rhinitis, omega-3 fatty acid supplement, health anxiety, somatization, and other measures on somatic health and socio-economic factors were all obtained by self-report. While using a population-based cross-sectional design in paper one, two and four, a historical cohort design was employed in the third paper. Long term sick leave (outcome) during 4-year follow-up was obtained from the National Insurance Administration and linked to HUSK data using national identity numbers. Results In the first study of this thesis, no association between anxiety, depression, and IgE levels was found, across different statistical approaches. The second study confirmed the well established association between anxiety, depression, and eczema, but somatization accounted for most of this association, while other factors such as female gender and omega-3 supplements were unable to contribute. The third study of the current thesis was not able to confirm the hypothesis suggesting that eczema is an independent and un-confounded risk factor for long term sick leave. Much of the eczema-sick leave association was accounted for by somatization, this was in contrast to the asthma-sick leave association, where somatization contributed little. In the last study, the association between eczema and somatization was found to be much stronger than the anxiety, depression, and eczema association. The association between eczema and somatization followed a dose-response pattern, as did all somatic symptoms in our index of somatization when analyzed separately. While the association between eczema and somatization was robust for adjustment for anxiety/depression, the anxiety/depression-eczema association was not robust for adjustment for somatization. Conclusions The main finding of this thesis was that somatization is strongly associated with eczema, and that this association was stronger than the well established association between anxiety, depression, and eczema. Individual symptoms constituting our somatization symptom index were equally associated with eczema, following a dose-response pattern. Somatization also explained most of the association between anxiety, depression, and eczema. Suggested contributing factors for this association, such as female gender and omega-3 fatty acid supplement, explained little. No association between anxiety, depression, and IgE levels was found, making us question the relevance of IgE as a contributing factor in the association between anxiety, depression, and eczema. Somatization also explained much of the association between eczema and long term sick leave, but this was not the case in sick leave following asthma, further underlining the significance of somatization in eczema. Our findings suggest that somatization is a more important factor in eczema than previously assumed. Somatization seems to be under-recognized in the psychodermatological literature, and this may also apply to clinical practice.
PublisherNorges teknisk-naturvitenskapelige universitet, Det medisinske fakultet, Institutt for nevromedisin
SeriesDoktoravhandlinger ved NTNU, 1503-8181; 2010:136
Dissertations at the Faculty of Medicine, 0805-7680; 441