Objective
The aim of this study was to assess the association between asthma and distress by whether symptoms of asthma present alone or are accompanied by atopy or bronchial reactivity to methacholine [bronchial responsiveness (BHR)], hence, to ascertain whether overreporting of asthma symptoms occurs in those with distress.
Methods
We studied 601 young adults in four groups: those with asthma symptoms and atopy or positive BHR, those with asthma symptoms only, those with atopy or positive BHR only, and controls. The main independent variables were the General Health Questionnaire-12 (GHQ-12) and 45 physical symptoms to assess somatization.
Results
The somatization score was highly associated with asthma symptoms alone and asthma symptoms with BHR or atopy, GHQ-12 with asthma alone and asthma and BHR or atopy related to a control group. After adjustment for somatization, GHQ-12 was not associated with the asthma outcomes.
Conclusions
Excess asthma symptom reporting due to psychological distress or somatization as a cause of the association is unlikely.
Psychological distress has been found associated with asthma in children and adults [1], [2], [3], [4], [5], [6] and [7]. One possible mechanism for explaining this consistent association is that psychological distress may be associated with somatization, and some respiratory symptoms would be misattributed to asthma symptoms [6] and [7]. Alternatively, psychological distress may be related to asthma through a not yet identified common factor associated with both asthma and psychological distress [2], psychosocial factors promoting an increase risk of asthma through the regulation of the immune system or other physiological mechanisms [8] and [9], or a mechanism of positive feedback between asthma and psychological distress resulting in exacerbation of asthma increasing the level of distress and psychological distress exacerbating asthma [7] and [10].
A misclassification of respiratory symptoms such as those of asthma could be the result of symptoms of common mental disorders in terms of psychological distress or somatization. This type of misattribution of respiratory symptoms would inflate the perceived prevalence of asthma, decrease the specificity of the condition, and decrease the effect size in etiological studies. In terms of management of the condition, it may lead to some subjects receiving inappropriate treatment. It is therefore important to explore whether this is the reason for an association between symptoms of common mental disorders and asthma. If we were able to exclude misattribution of respiratory symptoms as a reason for the association between symptoms of common mental disorders and asthma, we would be able to focus on exploring possible mechanisms for explaining such a strong association.
In epidemiological studies, asthma symptoms based on standardized questionnaires or physician-diagnosed asthma are the main criteria of assessing whether a person has asthma. Atopy or specific IgE in serum and bronchial responsiveness (BHR) to a physical or chemical challenge are often objective signs of subjects with asthma, but are not specific of asthma. In community studies such as the European Community Research Health Survey (ECRHS), it is usual to find that a large percentage of subjects may have asthma but not be sensitized or hyperresponsive to a challenge [11]. Physician-diagnosed asthma has the disadvantages of being dependent on an unstandardized clinical judgment and access to a doctor.
One way of deciding whether the association between symptoms of common mental disorders and asthma is due to misclassification of symptoms would be to assess whether the strength of this association varies according to the characteristics of subjects with asthma symptoms. If symptoms of common mental disorders led to the overreporting of asthma symptoms, there would be a gradient of psychological symptoms according to whether those reporting asthma symptoms had at least one of the objective characteristics positive BHR to methacholine or atopy, or not. There would be the most psychological distress or somatization in those with asthma symptoms only, intermediate distress in those with symptoms and positive BHR to methacholine or atopy, and the least in those not reporting asthma symptoms but with a positive BHR or atopy. Thus, the first aim of our study was to assess the strength of psychological symptoms, distress or somatization, and asthma symptoms in relation to their accompanying traits. A second aim was to assess whether an association between psychological distress and asthma is greatly reduced after adjustment for somatization in terms of physical symptoms. The reason for this aim was that most patients with psychological distress present with somatic symptoms, and in many communities, individuals are more willing to report somatic symptoms than psychological complaints [12] and [13].
