Psychosomatics 50:42-49, January-February 2009
doi: 10.1176/appi.psy.50.1.42
© 2009 Academy of Psychosomatic Medicine
The Impact of Psychological Distress on Functional Disability in Asthma: Results From The Canadian Community Health Survey
Norbert Schmitz, Ph.D.,
JianLi Wang, Ph.D.,
Ashok Malla, M.B.B.S., FRCPC, and
Alain Lesage, M.D., FRCPC
Received December 13, 2006; revised April 6, 2007; accepted May 18, 2007. From the Dept. of Psychiatry, McGill University, Douglas Hospital Research Centre, Montreal Canada; the Depts. of Psychiatry and Community Health Sciences, Faculty of Medicine, University of Calgary, Calgary, Canada; and the Centre de Recherche Fernand Seguin, University of Montreal, Hôpital Louis-H. Lafontaine, Montreal, Canada. Send correspondence and reprint requests to Norbert Schmitz, Ph.D., Douglas Hospital Research Centre, McGill University, 6875 LaSalle Blvd., Montreal, Quebec, H4H 1R3 Canada. e-mail: norbert.schmitz{at}mcgill.ca
© 2009 The Academy of Psychosomatic Medicine
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ABSTRACT
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BACKGROUND: Asthma is associated with decreased health-related quality of life and increased physical comorbidity and mortality, high rates of clinic visits and hospitalizations, and loss of productivity in the workplace. OBJECTIVE: The objective of the present study was to determine the joint effect of psychological distress and asthma on functional disability in a community sample. METHOD: The authors used data from The Canadian Community and Health Survey (N=62,274). Psychological distress was measured by the 10-item Kessler (K-10) instrument. Asthma, disability days, self-assessed health status, and long-term reduction in activities were assessed by personal interview. RESULTS: The prevalence of functional disability was higher in subjects with asthma and comorbid psychological distress than in individuals with either asthma or psychological distress alone. CONCLUSION: Detecting and managing psychological problems might be particularly beneficial for persons with asthma.
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INTRODUCTION
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Asthma is among the most common chronic medical conditions and is a major public health problem, both in prevalence and morbidity. The prevalence of asthma is steadily increasing in many industrialized countries, including Canada and the United States.1–3 Asthma is associated with decreased health-related quality of life4 and increased physical comorbidity and mortality, high rates of clinic visits and hospitalizations,5 and loss of productivity in the workplace.6
On the basis of clinical and population studies, there is growing evidence that people with asthma are at increased risk for psychiatric conditions such as depressive and anxiety disorders.7–14 For example, a community-based study from Germany found that severe asthma was associated with a significantly increased likelihood of having any anxiety disorder, panic disorder, social phobia, and generalized anxiety disorder.7 Although the association between asthma and psychological factors is well recognized, the impact of psychological distress on the health of people with asthma is also not well described. Clinic-based studies have found that subjects with asthma who reported high levels of psychological distress had greater healthcare utilization15 and poorer asthma-medication adherence.16 Smith et al.17 found that hospitalized patients with asthma and comorbid depressive symptoms were at high risk for poor adherence to asthma therapy after discharge.
Many of the studies that have investigated the association between asthma and psychological factors have used clinic or convenience samples, and few have examined the association of psychological distress with burden associated with asthma symptoms. On a population basis, it is unclear whether psychological distress has an impact on physical health and disability in people with asthma. Understanding the interaction of psychological distress and asthma on functional disability is critical for clinical practice in order to develop strategies for reducing disability in people with asthma. The use of population samples allows us to ascertain the proportion of disability attributable to psychological distress, to asthma, or to their combination. Using data from the recent Canadian Community and Health Survey,18 the objective of the present study was to evaluate the interactions between psychological distress and asthma, in relation to functional disability, in a community sample of people with asthma. We hypothesized that individuals with psychological distress and asthma would have higher functional disability than individuals with psychological distress or asthma alone, even after controlling for potentially confounding factors.
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METHOD
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Data Sources
The Canadian Community Health Survey (CCHS) is a cross-sectional survey that collects information related to health status, healthcare utilization, and health determinants for the Canadian general population.18 The CCHS Cycle 3.1 (CCHS 3.1) was conducted by Statistics Canada in 2005. The target population were household residents age 12 or older who were living in private dwellings in 10 provinces. This sampling frame covered 98% of the Canadian population. The survey participants were selected using multiple-staged, stratified random sampling procedures. Data were collected from 132,221 individuals by trained Statistics Canada interviewers. The response rate was 79%. The study was approved by an Advisory Committee consisting of representatives from health regions, all provincial and territories ministries of health, and Health Canada. Informed consent was obtained by interviewers from Statistics Canada.
The CCHS Cycle 3.1 questionnaire consisted of a main module, which was asked of all respondents, and several submodules. The main module included, among others, questions regarding sociodemographic characteristics, chronic conditions, general health, and disabilities. The optional modules included questionnaires that were chosen by regional representatives from a fixed list according to local needs and priorities.
The Psychological Distress module was administered in five provinces (Alberta, British Columbia, Prince Edward Island, Quebec, and Saskatchewan). In the present study, we included only subjects who were assessed for psychological distress, resulting in a sample size of 62,274 subjects (weighted data: 62,545).
Assessment
Nonspecific psychological distress was measured by the Kessler (K-10) scale.19,20 The K-10 is a 10-item, self-report questionnaire intended to yield a global measure of psychosocial distress on the basis of questions about the level of anxiety and depressive symptoms in the most recent 4-week period. Responses are recorded with a five-category scale (all of the time; most of the time; some of the time; a little of the time; and none of the time). Previous studies have suggested a classification of the total K-10 score into three categories: 0–5: low distress; 6–19: moderate distress; and 19–40: high distress.21
High levels of internal consistency have been reported for the K-10 (Cronbach  =0.92 in the Australian National Survey of Mental Health and Well-Being19). The validity of the K-10 as a measure of psychological distress, was supported in several surveys. The scale strongly discriminated between community cases and non-cases of DSM–IV depression and anxiety disorders in the Australian National Survey of Mental Health and Well-Being (Area under the Receiver Operating Characteristic [ROC[ curve: 0.879).19
Subjects were classified as having current asthma if they 1) reported ever being diagnosed with asthma by a health professional; and 2) if they had any asthma symptoms or asthma attacks in the past 12 months or had taken any medicine for asthma, such as inhalers, nebulizers, pills, liquids, or injections. All other subjects were classified as not having current asthma. No data on clinical asthma variables were available.
Also, respondents were asked to report previously-diagnosed medical conditions. In the present analyses, we focused on the most prevalent chronic conditions: diabetes, high blood pressure, heart disease, stomach or intestinal ulcers, arthritis/rheumatism, migraine headaches, and back problems.
Self-assessed health status was measured by a single question: ‘‘In general, would you say that your health is excellent, very good, good, fair, or poor?" The validity of this measure is supported by several studies showing that this single-item measure is a strong and independent predictor of morbidity and mortality.22
Long-term reduction in activities was assessed by asking subjects whether they had reduced the amount or kind of activity in daily life (at home or in other activities, such as transportation or leisure) because of a "long-term (>6 months) physical condition, mental condition, or health problem." Respondents who answered "never" were classified as being not restricted, whereas respondents who answered "sometimes" or "often" were classified as being restricted.
The CCHS also collected information about disability in the 2 weeks before the interview. Specifically, the participants were asked: "During the past 14 days, did you stay in bed at all because of illness or injuries, including any nights spent as a patient in a hospital?" and "During those 14 days, were there any days that you cut down on things because of illness or injuries?" In our analyses, an answer of "yes" to either question was considered to indicate the presence of disability. Also, subjects were asked about the number of disability-days (days that respondents had to stay in bed for all or most of the day or cut down on things for all or most of the day) during the 2 weeks before the survey. Disability-days were categorized into two categories (none versus one-or-more disability-days).
Both activity limitations and disability-days have been used as health indicators and health-related quality of life measures in community surveys.23–25 The sociodemographic and health-behavior factors that were studied included sex, age, education (low education: less than secondary school graduation; medium education: secondary school graduation; high education: postsecondary school graduation), and marital status (single, divorced, widowed, married, or with common-law partner), smoking (current smoker, former smoker, or never smoker), and alcohol consumption in the previous 12 months (no alcohol; up to 3 times a month; more than 3 times a month).
All subjects voluntarily participated in the study. Informed consent was obtained by interviewers from Statistics Canada; the data were released for public use in 2006.18
Statistical Analysis
In all analyses, the data were weighted to adjust for differential response rates and variation in probabilities of selection into the sample. Data analysis proceeded in two steps: First, sociodemographic and clinical characteristics were compared for subjects with and without asthma and for subjects with asthma with and without disability-days, fair/poor health status, and reduction in activities. Rao-Scott chi-square statistics were used for tests of association. This test applies a design-effect correction to the Pearson chi-square statistic computed from weighted frequencies. Second, multiple logistic regression26 was used to determine the independent odds of overall disability (disability-days: at least one disability-day versus no disability-days; health status: fair/poor health status versus good, very good, excellent health status; reduction in activities: not restricted versus restricted) across the 6 categories: 1) without asthma and with low psychological distress; 2) without asthma and with moderate psychological distress; 3) without asthma and with high psychological distress; 4) with asthma and with low psychological distress; 5) with asthma and with moderate psychological distress; and 6) with asthma and with high psychological distress. In all regression analyses, we controlled for sex, age, marital status, education, smoking, alcohol consumption, and chronic conditions (presence of at least one additional chronic condition) to account for their possible confounding effects.
All data were analyzed by Stata Statistical Software, Release 8.1,27 which includes commands for the analysis of complex survey data (survey commands incorporate the weighting and clustering of data).
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RESULTS
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Although fewer than half of the subjects of the original sample were used in the present analyses, there was no evidence of a selection bias. Our preliminary analysis found similar distributions of the sociodemographic and clinical variables for subjects that were included in the psychological distress module and those who were not included.
The population prevalence of current asthma was 6.6%. The prevalence of asthma was higher for the age-group 12 through 24 years (7.7%) than for other age-groups (25–34 years, 6.8%; 35–44 years, 6.2%; 45–59 years, 5.9%; >59 years, 6.3%; data not shown). Subjects with asthma were more often female, suffered more often from additional chronic conditions, and reported more psychological distress than subjects without asthma (Table 1).
More than one-fourth (27.3%) of the subjects with asthma reported at least one disability-day in the previous 2 weeks, whereas 15.4% of the those without asthma reported at least one disability-day in the previous 2 weeks. A similar pattern was observed for activity limitations and self-perceived health status: subjects with asthma reported more activity limitations (36.9%) and poorer health status (20.5%) than those without asthma (19.0% and 9.3%, respectively).
Subjects with adverse health status were more often female, more often current smokers, and suffered more often from additional chronic conditions than those with good health status (Table 2).
The relationships seen between asthma and adverse health outcomes were associated with psychological distress. There appears to be a progressive increase in the prevalence of disability-days across the three psychological distress categories: prevalence of at least one disability-day was 17% for those with asthma and low psychological distress, 35% for those with asthma and moderate psychological distress, and 69% for those with asthma and high psychological distress (Table 3). A similar association was observed for activity limitations (Table 4) and self-reported health status (Table 5): subjects with asthma and high psychological distress often reported more activity limitations and fair/poor health status (70% and 55%, respectively) than those with asthma and moderate psychological distress (45% and 26%, respectively) and those with asthma and low psychological distress (27% and 13%, respectively).
Table 3, Table 4, and Table 5 show adjusted odds ratios (ORs) of adverse health status by disease category. Logistic regression suggests that both asthma and psychological distress are strongly associated with adverse health status. The presence of psychological distress in asthma substantially increased the risk of adverse health status: the OR for disability days was 1.4 in subjects with asthma alone (activity limitations: 2.2; poor/fair health status: 2.0), 4.7 for subjects with high psychological distress alone (activity limitations: 7.6; poor/fair health status: 11.1), and 11.7 for subjects with both asthma and high psychological distress (activity limitations: 11.3; poor/fair health status: 16.6).
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DISCUSSION
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In this representative population survey, "disability" was more frequent in subjects with asthma and psychological distress than in subjects with either asthma or psychological distress alone. This effect was independent of confounding by lifestyle factors and sociodemographic characteristics and was evident across three different disability measures.
Our findings are consistent with those of other studies demonstrating that both psychological problems and disability are common in subjects with asthma.7–14 In a recent study, Stein et al.25 found that the presence of both major depression and asthma was associated with significantly greater likelihood of increased activity-reduction, absence from work, and disability-days, as compared with the presence of asthma without comorbid major depression.
The present study adds to this literature by showing that the odds of functional disability were significantly higher in individuals with asthma and comorbid psychological distress than in individuals with either psychological distress or asthma alone. The presence of both conditions resulted in more than additive effect in increasing risk.
Social models of disability have conceptualized disability as a phenomenon resulting from the interaction between the individual with a particular impairment and his or her environment.28 This approach acknowledges that aspects of the physical and social environments (e.g., living environment, family support) combine to determine the extent to which an individual is disabled. Our results, however, suggest that psychological distress plays an important role in the development of disability, as well. On the other hand, psychological distress cannot be separated entirely from and may, in fact, be related to, social and family support—something that these data are unable to examine.
There are obvious limitations to our study. First, our study was limited by the self-reporting of a previous asthma diagnosis before recruitment, and so may have included subjects who had even just one episode or were prescribed medication for asthma even if they did not meet criteria for asthma. We did not have information from general-practitioner or hospital records to confirm whether asthma had previously been diagnosed and the individual was unaware of that fact. Also, we have no clinical data on the severity of asthma, asthma symptoms, and asthma onset. Although we included only subjects with asthma attacks in the past 12 months or current asthma medication, it is possible that asthma-specific severity may moderate the association between psychological distress and disability in a different way.
Because of the cross-sectional nature of our study, we were unable to determine a causal relation between asthma, psychological distress, and disability. We do not have information on the course of psychological distress and disability. Psychological distress may occur as a reaction to disability, but may, as well, be a predictor for disability. Another possible limitation of the present study might be the use of self-report disability measures. Disability is a complex medical issue that has many dimensions—social, psychological, and medical. Other measures of disability (e.g., social functioning, employers’ absence records) might yield additional information.
The high burden of asthma appears to be related to poor asthma control.29 Asthma control relies on several behavioral factors (e.g., self-monitoring and treatment-adherence) that may be influenced by negative mood.16,30 Psychological distress may interfere with daily self-monitoring abilities and treatment-adherence,31 which may result in worse levels of asthma control, resulting in a cycle of ever-worsening outcomes (disability) for the individual. For example, depressive symptoms are associated with decreased performance on problem-solving tasks,32 which may influence decision-making and effectiveness of self-management of subjects with asthma.
Patients with severe, uncontrolled asthma are at high risk of experiencing frequent and potentially life-threatening attacks. Adaptive worrying about the "catastrophic" consequences of those attacks might trigger panic attacks.33 Patients with asthma and high levels of anxiety have been shown to have higher rates of emergency room visits34 and general asthma morbidity.14 Anxiety, which is a form of psychological distress, might increase disability in asthma: patients with asthma and comorbid anxiety have been shown to overmedicate with their bronchodilators,29 and they may also be less adherent to medication.16
In conclusion, our results suggest that there is a joint effect of psychological distress, depression, and asthma on disability. Paying greater attention to psychological distress as part of management of asthma would likely result in improved management of asthma, reduction of disability, and improvement in quality of life. The negative effect of psychological problems on disability suggests that research and social policies should focus on the treatment of these problems in asthma.
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ACKNOWLEDGMENTS
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This analysis is based on Statistics Canada’s Canadian Community Health Survey, Cycle 3.1 (2005), Public Use Microdata file, which contains anonymized data collected. All computations on these microdata were prepared by Norbert Schmitz, JianLi Wang, Ashok Malla, and Alain Lesage and the responsibility for the use and interpretation of these data are entirely that of the authors. All authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
This research was funded by the Canadian Institutes for Health Research (CIHR Grant MOP-79464). The principal author (NS) is supported by a Fonds de Recherche en Santé du Québec (FRSQ) Chercheur-Boursier fellowship.
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ABSTRACT
INTRODUCTION
