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Background: While patients' personality has been thought to affect all_ergic diseases, the association of asthma and psychological factors is still debated. Stress is believed to predispose to asthma, but no clear evidence of causality has been found. We have studied the role of psychological factors in prevalent as well as in incident asthma cases among the adult population.
Methods: A total of 11540 adults initiall_y aged 18–45 years responded to three questionnaires in 1975, 1981, and 1990, respectively. The association of psychological factors (including extroversion and neuroticism scales, subjective stress, and life satisfaction) and prevalent asthma was studied, as well as the predisposing effect of these factors on the risk of adult onset asthma. Logistic regression was used for risk calculations.
Results: Low life satisfaction was associated with asthma prevalence (age- and sex-adjusted OR=2.27: 1.04–4.93 for prevalent asthma among those with low life satisfaction compared to those with high life satisfaction), as was neuroticism (age and sex-adjusted OR=1.78:1.12–2.84 for those with a high neuroticism score compared to those with a low score). A high extroversion score was significantly associated with the risk of adult onset asthma among women (age-adjusted OR=2.72: 1.44–5.12 for new asthma among those with high score compared to those with a low extroversion score).
Conclusions: No specific personality type is associated with adult onset asthma, but there is a significant sex difference in the effect of psychological factors in asthma risk. A high extroversion score is a strong predictor of incident asthma among women. Prevalent asthma decreases life satisfaction and is associated with a high neuroticism score.
The psychological characteristics of asthmatic patients have been studied (1). No specific personality profile of asthmatic subjects has been found (2, 3), although there is evidence of an association between atopic illness and depression (4). Quality of life in asthma patients seems to be impaired both in younger (5) and in elderly people (6). An association between respiratory and psychiatric symptoms has also been found among healthy subjects without respiratory disease (7).
The association of stress and asthma has been studied previously, but a causal link between stress and asthma has not been established (8, 9). There are some retrospective studies reporting an association between onset of asthma and stressful life events (10, 11), as well as a prospective study showing an increased risk of asthma attacks among children who had experienced negative life events recently (12).
Still, it is questionable to what extent stress and other psychological factors may influence asthma. It is also necessary to distinguish the effects of asthma on patients' psychological condition from the role of psychological factors in the genesis of asthma. We did a prevalence study to estimate the relation between asthma and psychological factors and an incidence study to examine the role of stress, life satisfaction, and personality traits in the development of asthma in adulthood in a large, population-based sample.
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- Material and methods
The main finding of this study was the strong association between extroversion and incident asthma among women. The difference between men and women in the personality traits associated with asthma was also interesting. Low life satisfaction was associated with prevalent asthma, but not with incident cases.
The asthma diagnoses of the present study are based on the subjects' own reports of doctor-diagnosed asthma. Thus, personality might affect both the reporting of the disease and the seeking of treatment. It is also important to distinguish the effects of asthma on patients' psychological conditions from the possible personality features predicting asthma. An association between respiratory and psychiatric symptoms is found also among healthy subjects without respiratory disease (22). The advantage of a prospective study is the ability to control for the effect of early symptoms or manifestations of asthma on the reporting of psychological factors. Changes in the diagnostic criteria of asthma over time may also be a problem in studies with a long follow-up time. However, a previous study based on the Finnish Twin Cohort found no significant difference in incidences of adult-onset asthma between 1982–90 and 1976–1981 (21). In the present study, we used in all_ questionnaires an asthma question that has been found to have a high validity (23). In addition, for incidence estimation, analysis of the initiall_y asthma-free population was based on data from two questionnaires.
The Eysenck Personality Inventory used in this study measures the psychosocial status of a subject in two major dimensions: the degree of neuroticism, also termed the “stable-unstable” dimension, and the degree of extroverted behavior (18). Genetic and experiential effects are involved in personality development, and both are modulated by age and sex (19). However, in the present study, the intraindividual levels of extroversion and neuroticism were relatively stable in the two questionnaires 6 years apart. To control the variation of measures used over time, we used a mean score of two measurements if available.
Previous studies have not shown any specific personality profile in asthmatic patients, while emotional sensitivity (3) and anxiety (24) have been suggested. In the present study, the risk of developing asthma in adulthood was increased among women with a high extroversion level. In contrast, the association with prevalent asthma and extroversion was not significant. Thus, it is possible that asthma itself can modify one's personality. In addition to the possible personality-dependent reporting and treatment-seeking differences discussed above, extrovert women might have a different lifestyle from that of the more introvert ones. The association of smoking and adult onset asthma is not clear. We did not find any effect of smoking on asthma risk with the relatively crude classification used in the present study. However, a high extroversion score was most common among current smokers. The number of cigarettes smoked and the age when smoking began may also be associated with extroversion, thereby partly explaining the increased risk seen in extrovert women. Personality might also affect one's choice of profession and residential environment, and in that way predispose extrovert persons to asthma.
Men with a high neuroticism score had an almost twofold higher risk of asthma than those with a low score. As discussed above, personality might have an effect on one's inclination to seek treatment, and partly contribute to the additional number of new asthma diagnoses among men with a high neuroticism score. This may also partly explain the sex difference seen in the present study.
The life satisfaction scale used in this study is an index of global satisfaction with the current life situation. Low life satisfaction was strongly associated with prevalent asthma. This effect was seen also among women without symptoms of COPD, which are known to worsen the quality of life. Controlling also for moderate respiratory symptoms instead explained the low life satisfaction of asthma patients. Thus, it is interesting that also asthmatic women without severe symptoms felt themselves significantly dissatisfied with their lives. However, it should be remembered that the asthma prevalence of the present study is based on diagnoses done before 1982. The treatment of asthma has improved significantly over recent decades, and asthma patients probably now find their lives more satisfactory.
The high correlation between life satisfaction and the score of the Beck Depression Inventory indicates that life satisfaction also measures aspects of depressive symptomatology (17), as does the neuroticism score. Janson et al. have found an association between reported respiratory symptoms and psychological status, but no evidence that persons with diagnosed asthma had more anxiety or depression than those without asthma (7). Michel (3) also suggests that atopic patients, instead of being typicall_y depressive, are characterized by an increased emotional sensitivity. Another study, based on the 1990 questionnaire of the Finnish Twin Cohort, found an association between atopic illness and depression (4). In addition to low life satisfaction, neuroticism was also associated with prevalent asthma in the present study, thus indicating an association between asthma and depressive symptoms.
In the present study, the subjects' own experience of daily stress was used to assess the amount of stress. The face validity of this kind of measure of stress is supported by earlier studies of the Finnish Twin Cohort, in which it has predicted mental disorders (16) and peptic ulcer (15). We did not find any significant risk effect of stress on incident asthma, and the slightly increased risk found among stressed men decreased when adjusted for respiratory symptoms.
We conclude that the effect of psychological factors is different among men and women. Personality might affect the reporting of asthma, and this may explain part of the sex differences seen in the present results. Prevalent asthma decreases life satisfaction and increases neuroticism, thus lending further support to the possible association between asthma and depression. A high extroversion score was a strong predictor of incident asthma among women. Thus, factors associated with the extrovert personality should be studied further to find possible risk factors of adult asthma.