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Asthma and mental disorders in Canada: Impact on functional impairment and mental health service use
Journal of Psychosomatic Research 68 (2010) 165 – 173
Asthma and mental disorders in Canada: Impact on functional impairment and mental health service use Renee D. Goodwin a,⁎, Jina Pagura b,d , Brian Cox b,c,d , Jitender Sareen b,c a
Mailman School of Public Health, Columbia University, New York, NY, USA b Department of Psychiatry, University of Manitoba Winnipeg, MB, Canada c Department of Community Health Science, University of Manitoba Winnipeg, MB, Canada d Department of Psychology, University of Manitoba Winnipeg, MB, Canada Received 23 April 2008; received in revised form 21 May 2009; accepted 16 June 2009
Abstract Objective: The goal of this study is to examine the association between asthma and mental disorders and the impact of asthma and mental disorder comorbidity on functional impairment and mental health care service use among adults in the community. Methods: Data came from the Canadian Community Health Survey Cycle 1.2 (N=36,984; age ≥15 years; response rate, 77%). Mental disorders were assessed using the Composite International Diagnostic Interview. Chronic physical health conditions, quality of life, and disability were also assessed. Asthma diagnoses were based on self-report of having been diagnosed with asthma by a health care professional. Results: Asthma was associated with a significantly increased likelihood of a range of mental disorders among adults in Canada, with the strongest links between asthma and posttraumatic stress disorder, mania, and panic disorder. Adults
with both mental disorders and asthma had significantly higher rates of functional impairment and use of mental health services, compared with those with either asthma or mental disorders but not both. Conclusions: Our findings provide new information suggesting that adults in the community with asthma and mental disorders have higher levels of both short- and long-term healthcondition-related functional disability and greater use of mental health services, compared with those with asthma without mental disorders. Results are also consistent with previous studies showing a significant link between asthma and mental disorders. Implications of these findings for efforts aimed at secondary prevention and improving treatment strategies for individuals with both asthma and mental disorders are discussed. © 2010 Published by Elsevier Inc.
Keywords: Asthma; Mental disorders; Chronic disease; Health service use; Epidemiology; Comorbidity
Introduction Several national studies have shown links between asthma and mental disorders [1,2]. Examining this problem in a range of geographic areas is important, as there is wide geographic variation in the prevalence of asthma [3,4]. There is also substantial geographic variation in the prevalence of potential causes and correlates of asthma [5]. Mounting data suggest that understanding these ⁎ Corresponding author. Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th Street, Rm. 1706, New York, NY 10032, USA. Tel.: +1 212 342 0422; fax: +1 212 342 5170. E-mail address: [email protected] (R.D. Goodwin). 0022-3999/09/$ – see front matter © 2010 Published by Elsevier Inc. doi:10.1016/j.jpsychores.2009.06.005
geographical disparities may be important not only for identifying possible causes of the asthma epidemic but also in identifying more effective asthma prevention and management strategies. No study to date has examined the relationship between asthma and mental disorders in a nationally representative sample in Canada. Growing evidence also suggests that the comorbidity of asthma and mental health problems may have a potentially significant impact on daily functioning and mental health care service use. For instance, one study by Feldman et al. [6] found that asthma patients with at least one mental disorder reported significantly higher levels of asthma symptoms, impairment in daily functioning, medication use, and emergency room (ER) treatment for
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asthma, compared to patients with asthma without psychiatric disorders. This study did not find any difference, however, in actual pulmonary function between patients with and without a mental disorder. Another recent study showed an association between comorbid anxiety and higher levels of functional impairment among adults with respiratory disease, compared with those without anxiety [7]. A study in Australia additionally found significant links between asthma and psychological distress and mental health problems among adults [8], yet no previous community-based study has investigated the relationship between comorbidity of asthma and mental disorders on functioning and health service use in a national sample in Canada. Both asthma and mental disorders are costly to both the individual and society. Asthma is responsible for US$4912 per patient in health care costs [9] and 10.1 million [10] missed work days per year while major depression is expected to be the single leading cause of disability worldwide by the year 2020 [11], while there is some evidence to suggest that comorbidity of asthma and mental disorders is associated with higher levels of impairment. As health care use and help-seeking behavior are often driven by impairment levels and other factors, beyond clinical pathology, it is conceivable that rates of service use are affected by comorbidity as well. The current study aims to fill several gaps in existing research. First, the study will examine the relationship between asthma and mental disorders in a large nationally representative sample of adults in Canada. Second, the study will investigate the relationship between mental disorders and impairment in short-term and long-term functioning in various domains among adults with asthma. Third, the study will examine the relationship between asthma, mental disorders, and level of health service use. Finally, the study will investigate the role of differences in demographic characteristics and comorbid physical health conditions within these associations. We hypothesize that asthma will be associated with higher levels of mental disorders and that having both asthma and mental disorders will be associated with greater functional impairment and health service use, compared with asthma alone. We also predict that differences in demographic characteristics and other comorbid health conditions will play a role in these relationships but will not fully explain these associations.
Methods Sample Data came from the public use files of a survey designed by Statistics Canada under the provisions set out in the federal Statistics Act, the Canadian Community Health Survey cycle 1.2 (CCHS 1.2; N=36,984; age 15
and older; response rate, 77%) [12]. The target population was persons living in private dwellings in the 10 Canadian provinces, excluding persons living in the three territories or in First Nations Communities and clientele of institutions. A multistage stratified cluster design was utilized to ensure that the sample would be representative of the Canadian general population. Trained lay interviewers who received additional training to increase their sensitivity to mental health issues conducted the interviews, in either English or French depending on the preference of the respondent, using the ComputerAssisted Personal Interviewing method. A detailed description of the method of selection for household interviews is reported elsewhere [13]. Measures Sociodemographics Sex, age, education, marital status, and household income were included in the analysis. Income quartiles were derived in the following way: lowest income, bUS$15,000 for one or two people in the household, bUS$20,000 for three or four people in the household, bUS$30,000 for five or more people in the household; lower middle income, US$15,000– 29,999 for one or two people in the household, US$20,000– 39,000 for three or four people in the household, US $30,000–59,999 for five or more people in the household; upper middle income, US$30,000–59,999 for one or two people in the household, US$40,000–79,999 for three or four people in the household, US$60,000–79,999 for five or more people in the household; highest income, NUS$60,000 for one or two people in the household, NUS$80,000 for three or more people in the household. Asthma Asthma was assessed in the CCHS 1.2 in the chronic health conditions section. Respondents were told “We are interested in long-term conditions which are expected to last or have already lasted 6 months or more and that have been diagnosed by a health professional.” Respondents were then asked “Do you have asthma?” Psychiatric disorders Lifetime and past-year diagnoses of major depression, mania, panic attacks, panic disorder, social phobia, and agoraphobia and past-year diagnoses of alcohol dependence and drug dependence were assessed using the World Health Organization Composite International Diagnostic Interview (CIDI), which generates diagnoses according to definitions in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) [14–16]. Only pastyear diagnoses of alcohol and drug dependence exist due to a skip error in the questionnaire that precluded assessment of lifetime symptoms for respondents who were asked the pastyear dependence questions. Posttraumatic stress disorder (PTSD) was assessed in the chronic conditions section of the
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survey. Respondents were asked whether they had been diagnosed with PTSD. As described above, this diagnosis was described as being diagnosed by a health care professional and lasting at least 6 months. This methodology is consistent with the previous work by Frayne et al. [17]. Past-2-week disability Past-2-week disability was assessed with four variables. Variables reflecting disability due to physical health problems and disability due to mental health problems were calculated by totaling the number of days in the past 2 weeks that the respondent was in bed for the entire day or for most of the day (due to physical health problems or mental health problems). Two additional items asked respondents whether, during the last 2 weeks, there were any days where they cut down on things they normally did because of illness or injury and any days where it took extra effort to perform to their usual level at work or at their other daily activities because of illness or injury. In line with the methodology used in previous work with the CCHS [7,18,19], these variables were dichotomized into 0 versus 1 or more days of disability since their distributions were skewed with the majority of respondents endorsing 0 days of disability. Long-term disability Respondents were asked if a long-term physical health condition, mental condition, or health problem had reduced the amount or kind of activity (1) “at home”, (2) “at school”, (3) “at work”, or (4) “in other activities, for example, transportation or leisure”. Additionally, respondents were asked whether they had any difficulty “hearing, seeing, communicating, walking, climbing stairs, bending, learning, or doing any similar activities”. For each item, response choices were (1) sometimes, (2) often, or (3) never. Due to the skewed distributions of these variables, with the great majority of the sample reporting “never” for all areas of functioning, respondents endorsing “never” for each area of functioning were categorized as “not limited”, while those endorsing limitation sometimes or often were categorized as “limited.” This methodology has been utilized in previous work with CCHS data sets [7,18,19]. Health service use Three variables were used as indices of health service use in the current study. The attainability of mental health services in Canada is similar across most provinces in that it does not limit number of visitations [20]. One item assessed hospitalization. Respondents were asked whether they had ever been hospitalized overnight or longer in any type of health care facility to receive help for problems with their emotions, mental health, or use of alcohol or drugs. Another reflected any use of the ER. Respondents indicating that they had ER contact with any health professional were categorized as having ER use in the past year. The third treatment index used in this study reflected use of antianxiety
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medication. Respondents were asked whether they had used any medication to decrease anxiety or nervousness in the past year. Physical health conditions As described above, long-term conditions that are expected to last or have already lasted 6 months or more and have been diagnosed by a health care professional were assessed in the chronic health conditions section. There were 21 chronic physical health conditions assessed. These include food allergies, other allergies, asthma, fibromyalgia, arthritis or rheumatism, back problems, high blood pressure, migraines, chronic bronchitis, emphysema or chronic obstructive pulmonary disease, diabetes, epilepsy, cancer, stomach or intestinal ulcers, stroke, bowel disorder, cataracts, glaucoma, thyroid condition, chronic fatigue syndrome, and multiple chemical sensitivities. Respondents' indications of the presence of each of these chronic conditions were used to create a dichotomous variable reflecting comorbidity of physical health conditions. Individuals who had zero or one chronic condition were categorized as not exhibiting comorbidity of physical health conditions while those who had two or more physical health conditions were categorized as exhibiting comorbidity of physical health conditions. Analytic strategy First, cross tabulations were used to examine the frequency and proportions of asthma among different categories of sociodemographic variables described above. Chi-square tests of association were also used to examine relationships between sociodemographic factors and the presence of asthma. Next, the association between mental disorders and asthma was assessed using logistic regression. Asthma was entered as an independent variable predicting the presence of each mental disorder in bivariate regressions. These regressions were then repeated after adjusting for sociodemographics [adjusted odds ratio (AOR)]. Functional limitations and service use were examined using logistic regression as well. First, variables reflecting the presence of asthma, the presence of any mental disorder, and the interaction between these two variables were entered as predictors for each functional limitation and service use variable after adjusting for demographic factors, to examine multiplicative effects. Second, to examine more specific, additive effects, a four-category variable based on the presence versus absence of asthma and mental disorders (1=neither asthma nor mental disorder; 2=asthma, no mental disorders; 3=any mental disorder, no asthma; and 4=asthma and any mental disorder) was entered as an independent variable predicting each functional limitation and service use variable after adjusting for demographics (AOR-1) and after adjusting for demographics and comorbidity of physical health conditions (AOR-2). The additional adjustment for comorbidity of physical health conditions was utilized to demonstrate that associations were specific to asthma instead
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of reflecting chronic physical conditions in general. Similar methodologies have been used to examine other indices of functioning and their relationships with mental and physical health in German [21] and Canadian [7] samples. Finally, associations between specific mental disorders and functional limitations and service use were examined among individuals with asthma. All mental disorders assessed were entered simultaneously in a model predicting each functional limitation and service use variable, after adjusting for demographics. For all analyses, appropriate statistical weights provided by Statistics Canada were applied to ensure that the data were representative of the general population. Taylor Series Linearization, a variance estimation procedure, was also used in all analyses to account for the complex sampling design of the survey [13]. This was conducted with SUDAAN software [22] using the statistical weight and stratification information within the CCHS 1.2 public use data set [13].
Results Sociodemographic characteristics associated with asthma among adults in Canada Among adults in Canada, asthma was more common among those who are younger, who are female, and who have never been married or are divorced (see Table 1). In
addition, asthma is more frequently found among adults with less formal education and lower income. All associations were significant at the Pb.001 level. Association between asthma and mental disorders All mental disorders were more common among adults with asthma, compared with those without asthma with the exception of past-year illicit drug dependence (see Table 2). Strong associations emerged between asthma and PTSD and between asthma and mania, followed by panic attacks and panic disorder. After adjusting for differences in demographic characteristics, these associations were attenuated slightly but remained statistically significant. Association between asthma and mental disorder comorbidity and functional limitations There was a significant interaction between asthma and the presence of any mental disorder for the outcome of 2week disability due to mental health and not for the other disability outcomes. In regressions using the four-category independent variable, having asthma or a mental disorder was associated with significantly increased impairment in past-week and impairment in long-term functioning after adjusting for sociodemographic factors (see Table 3). Adults with asthma and at least one mental disorder showed substantially higher levels of impairment compared with
Table 1 Sociodemographic characteristics associated with asthma among adults in Canada
Age (years) 15–24 25–44 45–64 65+ Gender Male Female Marital status Married/cohabit Separated/divorced/widowed Never married Education Up to 8th grade 9–13th grade High school graduate At least some post-secondary education Income Lowest Lower middle Upper middle Highest
Without asthma (n=33,622), n (%)
With asthma (n=3358), n (%)
χ2 (df)
4965 (15.99) a 11,657 (38.05) 9915 (30.96) 7085 (15.00)
708 (22.52) 1155 (37.90) 845 (25.63) 650 (13.95)
14.99 (3) ⁎⁎⁎
15,550 (49.93) 18,072 (50.07)
1222 (40.82) 2136 (59.18)
46.30 (1) ⁎⁎⁎
17,706 (62.52) 7166 (12.64) 8712 (24.84)
1476 (53.31) 791 (14.80) 1086 (31.89)
24.67 (2) ⁎⁎⁎
3329 (8.16) 6168 (16.93) 5949 (19.09) 17,974 (55.82)
375 (9.11) 720 (20.50) 548 (17.50) 1687 (52.89)
4.83 (3) ⁎⁎
4337 (9.84) 7330 (20.93) 10,829 (35.96) 8030 (33.27)
631 (14.44) 748 (20.91) 953 (33.87) 687 (30.78)
9.79 (3) ⁎⁎⁎
All n's are unweighted. All percentages are weighted. a Percentages can be interpreted as follows: 15.99% of respondents without asthma were 15–44 years old. ⁎⁎ P≤.01. ⁎⁎⁎ P≤.001.
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Table 2 Association between asthma and mental disorders among adults in Canada
Mental disorders Any mental disorder Major depression Manic episode Panic disorder Panic attack Social phobia Agoraphobia PTSD Past-year mental disorders Alcohol dependence Illicit drug dependence
Without asthma (n=33,622), n (%)
With asthma (n=3358), n (%)
Unadjusted OR (95% CI)
AOR (95% CI)
10,620 (31.52) a 4077 (11.69) 785 (2.18) 1175 (3.46) 6804 (19.81) 2683 (7.81) 489 (1.47) 384 (0.89)
1487 (44.07) 635 (17.92) 153 (4.43) 222 (6.29) 1014 (29.06) 376 (11.22) 78 (2.27) 94 (2.35)
1.71 (1.54–1.91) ⁎⁎⁎ 1.65 (1.43–1.90) ⁎⁎⁎ 2.08 (1.62–2.69) ⁎⁎⁎ 1.87 (1.51–2.33) ⁎⁎⁎ 1.66 (1.48–1.86) ⁎⁎⁎ 1.49 (1.26–1.76) ⁎⁎⁎ 1.56 (1.11–2.20) ⁎ 2.69 (1.97–3.66) ⁎⁎⁎
1.66 (1.48–1.86) ⁎⁎⁎ 1.61 (1.39–1.87) ⁎⁎⁎ 1.93 (1.47–2.53) ⁎⁎⁎ 1.73 (1.38–2.17) ⁎⁎⁎ 1.62 (1.43–1.83) ⁎⁎⁎ 1.45 (1.22–1.73) ⁎⁎⁎ 1.41 (0.98–2.03) 2.62 (1.89–3.63) ⁎⁎⁎
923 (2.48) 250 (0.75)
124 (3.63) 38 (1.04)
1.48 (1.16–1.90) ⁎⁎ 1.38 (0.89–2.15)
1.29 (0.98–1.71) 1.36 (0.86–2.15)
All n's are unweighted. All percentages are weighted. AOR=adjusted for gender, age, education, income, and marital status. a Percentages can be interpreted as follows: 31.52% of respondents without asthma had any mental disorder. ⁎ P≤.05. ⁎⁎ P≤.01. ⁎⁎⁎ P≤.001.
individuals either with asthma and no mental disorders or with a mental disorder but no asthma. Additionally, having both asthma and mental disorders was also associated with significantly higher rates of recent work loss due to both physical and mental health. After adjusting for differences in demographic characteristics as well as comorbidity of physical health conditions, the link between comorbid asthma and mental disorders and increased rates of functional impairment remained strong and statistically significant (see Table 3), compared with limitations among those with asthma and no mental disorder. In contrast, most odds ratios were no longer significant after these adjustments when compared to individuals with a mental disorder and no asthma. Individuals with a mental disorder only were significantly more likely than individuals with asthma only to exhibit functional limitations in all domains, with the exception of functional limitations at school, after adjusting for both sociodemographics and comorbidity of physical health conditions. More specifically, among adults with asthma, major depressive episode and social phobia were associated with significantly increased odds needing extra effort to perform at usual level, limitation in normal activities, and limited activity in home and school. Panic disorder was also associated with limitation in normal activities and limited activities at home, work, and other domains. No other mental disorders, with the exception of a link between drug dependence and extra effort needed to perform at usual level, were found between specific mental disorders and functional limitations (results not presented). Association between asthma and mental disorder comorbidity and mental health service use There was a significant interaction between asthma and the presence of any mental disorder for the outcome of any ER contact. There were no other significant interactions for
health service use outcomes. In regressions using the fourcategory independent variable, having both asthma and mental disorders was associated with significantly higher rates of overnight hospitalization and use of antianxiety medication in comparison to those with mental disorders without asthma or those with asthma without a mental disorder (see Table 4). Individuals with a mental disorder only were significantly more likely than individuals with asthma only to report being hospitalized overnight or longer and taking antianxiety medication after adjusting for both sociodemographics and comorbidity of physical health condition. More specifically, among adults with asthma, major depressive episode, mania, panic disorder, social phobia, and agoraphobia were associated with increased odds of overnight hospitalization; social phobia and agoraphobia were associated with any ER use; and major depressive episode, panic disorder, and social phobia were associated with use of antianxiety medication (results not presented).
Discussion The four main findings of this study will be summarized, considered in the context of previously available data, and then discussed in terms of their implications for future research. First, we found that asthma is associated with a significantly increased likelihood of a range of mental disorders among adults in Canada. Second, we found that having both asthma and mental disorders was associated with significantly higher levels of functional impairment and limitations in functioning, compared with asthma alone. Third, results showed that having both asthma and mental disorders was associated with significantly higher levels of mental health service use, compared with use among adults with mental disorders without asthma. Fourth, our results
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Table 3 Association between asthma and mental disorder comorbidity and functional limitations in Canada Asthma and mental disorder group compared to mental-disorder-only group
n (%)
AOR-1 (95% CI)
82 (0.33) a
n (%)
n (%)
n (%)
AOR-1 (95% CI)
AOR-2 (95% CI)
29.08 (8.94–94.63) ⁎⁎⁎ 27.47 (8.44–89.42) ⁎⁎⁎ 1.76 (1.22–2.53) ⁎⁎⁎ 1.21 (0.83–1.76)
4 (0.12)
302 (2.31)
84 (4.06)
2343 (9.92)
300 (14.14)
1824 (16.30)
386 (25.40)
2.17 (1.68–2.81) ⁎⁎⁎
2.03 (1.57–2.63) ⁎⁎⁎
1.79 (1.46–2.18) ⁎⁎⁎ 1.17 (0.95–1.44)
2096 (8.92)
270 (12.84)
1876 (16.35)
393 (25.45)
2.44 (1.87–3.17) ⁎⁎⁎
2.28 (1.75–2.96) ⁎⁎⁎
1.78 (1.45–2.17) ⁎⁎⁎ 1.16 (0.94–1.42)
2083 (8.60)
304 (14.09)
2098 (18.19)
430 (28.30)
2.57 (2.00–3.31) ⁎⁎⁎
2.40 (1.86–3.09) ⁎⁎⁎
1.84 (1.52–2.24) ⁎⁎⁎ 1.20 (0.99–1.46)
5587 (20.21)
651 (31.21)
3178 (27.26)
662 (42.82)
2.13 (1.68–2.69) ⁎⁎⁎
1.92 (1.52–2.42) ⁎⁎⁎
2.32 (1.94–2.78) ⁎⁎⁎ 1.36 (1.14–1.64) ⁎⁎⁎
3539 (12.47)
514 (25.56)
2505 (20.30)
582 (36.42)
2.23 (1.74–2.88) ⁎⁎⁎
1.96 (1.53–2.50) ⁎⁎⁎
2.70 (2.24–3.26) ⁎⁎⁎ 1.47 (1.22–1.78) ⁎⁎⁎
146 (3.63)
29 (11.71)
213 (11.45)
54 (19.42)
1.37 (0.64–2.94)
1.22 (0.56–2.67)
1.75 (1.03–2.97) ⁎⁎⁎ 0.89 (0.49–1.61)
1118 (7.39)
156 (15.50)
1232 (15.56)
257 (27.44)
2.26 (1.59–3.22) ⁎⁎⁎
2.08 (1.46–2.97) ⁎⁎⁎
2.38 (1.87–3.03) ⁎⁎⁎ 1.23 (0.96–1.57)
3382 (12.53)
480 (24.75)
2540 (21.82)
559 (35.01)
1.91 (1.49–2.46) ⁎⁎⁎
1.70 (1.33–2.16) ⁎⁎⁎
2.11 (1.75–2.54) ⁎⁎⁎ 1.18 (0.98–1.41)
All n's are unweighted. All percentages are weighted. AOR-1=adjusted for gender, age, education, income, and marital status. AOR-2=adjusted for gender, age, education, income, marital status, and comorbidity of physical health conditions (dichotomous one or no disorder vs. two or more disorders). a
AOR-2 (95% CI)
Percentages can be interpreted as follows: 0.33% of respondents with neither asthma nor any mental disorder had 2-week disability due to mental health. ⁎⁎⁎ P≤.001.
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Past-2-week disability Two-week disability due to mental health Two-week disability due to physical health Cut down on things normally done Took extra effort to perform at usual level Long-term disability Limited in normal activities Limited in amount or kind of activity at home Limited in amount or kind of activity at school Limited in amount or kind of activity at work Limited in amount or kind of activity in other activities
Without asthma or With asthma but With mental disorder With asthma and mental disorder without mental but without asthma mental disorder Asthma and mental disorder group (n=22,172) disorder (n=1786) (n=10,620) (n=1487) compared to asthma-only group
a Percentages can be interpreted as follows: 1.80% of respondents with neither asthma nor any mental disorder had been hospitalized overnight or longer. ⁎⁎⁎ P≤.001.
10 (0.03) 704 (2.45)
485 (1.80)
Hospitalized overnight or longer Any ER use Antianxiety medication
All n's are unweighted. All percentages are weighted. AOR-1=adjusted for gender, age, education, income, and marital status. AOR-2=adjusted for gender, age, education, income, marital status, and comorbidity of physical health conditions (dichotomous one or no disorder vs. two or more disorders).
1.56 (0.53–4.58) 1.24 (0.98–1.56) – 5.05 (3.52–7.23) ⁎⁎⁎ 11 (0.69) 274 (17.09) 54 (0.39) 1307 (10.95) 0 (0.00) 84 (3.96)
62 (2.16)
1394 (10.71)
269 (14.60)
– 5.46 (3.80–7.84) ⁎⁎⁎
1.54 (0.57–4.17) 1.70 (1.35–2.14) ⁎⁎⁎
AOR-2 (95% CI)
1.10 (0.88–1.37) 1.36 (1.10–1.69) ⁎⁎⁎ 7.99 (5.13–12.44) ⁎⁎⁎ 8.40 (5.40–13.08) ⁎⁎⁎
AOR-1 (95% CI) AOR-2 (95% CI) AOR-1 (95% CI) n (%) n (%) n (%)
a
n (%) Services
With asthma and mental disorder (n=1487) With mental disorder but without asthma (n=10,620) With asthma but without mental disorder (n=1786) Without asthma or mental disorder (n=22,172)
Table 4 Association between asthma and mental disorder comorbidity and health service use among adults in Canada
Asthma and mental disorder group compared to asthma-only group
Asthma and mental disorder group compared to mental-disorder-only group
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indicated that demographic characteristics did not explain the observed links between asthma, mental disorders, and functional impairment among adults in Canada. Our findings on the relationship between asthma and mental disorders are remarkably consistent with previous community-based results from Germany [1] and New Zealand [2] both in terms of the overall strength of the associations between asthma and mental disorders (i.e., strength of the odds ratio) and in terms of the relative strength of the relationships between asthma and each of the mental disorders assessed. We found the strongest link between asthma and PTSD, although this association cannot be directly compared with either previous study as they did not assess PTSD. In addition, PTSD was not assessed with the CIDI in this study as were the other mental disorders; hence, the accuracy of this diagnosis is somewhat unclear. No previous community-based study has examined the relationship between asthma and PTSD, though results from recent twin [23] and clinical studies have suggested strong links possibly due to traumatic or life-threatening medical situations among those with asthma [24–26]. Consistent with previous population-based and clinical findings, there were also strong links between asthma and panic disorder and panic attacks [1,2,27,28]. Our results provide new data on the potential impact of having both asthma and mental disorders on functional impairment among adults in the community. These findings are consistent with previous results from primary care and community studies showing depression and other mental disorders associated with increased functional impairment among adults with diabetes and other physical health problems [29,30]. Although this is purely speculative since mental disorders are measured only by lifetime status, the finding that there is only a significant interaction between asthma and mental disorders in predicting impairment in the past 2 weeks is intriguing and has potential clinical implications suggesting that the comorbidity does indeed have a detrimental impact above and beyond that of either disorder independently. It may also be that temporality is critical to the impact this comorbidity has; the specificity of the finding to past-2-week impairment may reflect that both need to occur simultaneously for the impact to be evident and that, therefore, this is best reflected in the most recent time assessment. The possibility that temporality of the comorbidity of asthma and mental disorders may affect the related impairment/severity of disease is consistent with findings from the German study that found stronger associations between more severe asthma and past-year, compared with lifetime, mental disorders [1]. The potential conclusion that having both asthma and mental disorders concurrently, rather than comorbid during the lifetime but not at the same point in time, makes clinical sense from the perspective that coping with more than one disease concurrently would translate into greater impairment. It is further conceivable that, for instance, there may be an interaction between mental disorders and asthma on
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respiratory functioning, which could lead to greater impairment in several areas. Future studies that can more specifically examine these patterns with longitudinal data, more detailed description of types of impairment, and refined respiratory measures may be helpful in developing treatment strategies for patients with both conditions. Of particular interest, these findings suggest that having both asthma and mental disorders is associated with a significantly increased level of use of mental health services among adults, compared with those with mental disorders without asthma. It is not clear why this would be the case. It also seems as if much of this difference in use is explained by differences in demographic characteristics between those with mental disorders with asthma and those without. Previous clinical studies have specifically shown that asthma patients with use of mental disorders used higher levels of asthma medications, and asthma services, compared with asthma patients without mental disorders [31], though no previous study has demonstrated a link with mental health services. Limitations of this study should be considered when interpreting results. First, asthma diagnosis was by selfreport and we have no information on duration, age of onset, or severity. In addition, we did not have information on treatment or pulmonary function, although results of a community-based study that measured pulmonary function, which found links between respiratory disease and mental health, are consistent with these findings [32]. Second, asthma and mental disorders tend to be strongly associated with sociodemographic characteristics, and the level of variability of sociodemographic characteristics in Canada may differ from other communities, such as the United States, and therefore, replication may be useful in a variety of communities in order to understand the role of sociodemographic characteristics in these links. Third, as these data are cross-sectional, it was not possible to draw any causal conclusions. Fourth, methods available for diagnosing PTSD were limited, and additional studies replicating these findings using more commonly used standardized measures will be useful. Lack of information on smoking status is also a shortcoming of the study, since smoking can be related to both asthma-like symptoms and mental disorders, resulting in the possible overestimation of the results. In sum, these results replicate findings of a link between mental disorders and asthma among adults in the community, as has previously been observed in other countries. Our findings provide initial evidence suggesting that comorbidity of asthma and mental disorders is associated with increased functional impairment, compared with either disorder alone with some evidence of an interactive effect. Results also suggest that having both asthma and mental disorders appears to be associated with higher levels of mental health service use. We also found that specific mental disorders, most commonly major depression, panic disorder, and social phobia, were most strongly associated
with impairment and service use among adults with asthma, while other mental disorders had variable or nonsignificant effects. The impact of this comorbidity on impairment and service use provides evidence supporting the call to develop both screening measures for mental disorders among patients with asthma and to develop treatment strategies specific to addressing these problems when they co-occur [33]. Future clinical and epidemiologic studies that can begin to investigate these new strategies are needed. In addition, future investigations using longitudinal, prospective data to investigate these links may be informative into understanding the etiology of this pattern of comorbidity.
Acknowledgments This research was supported by a Canadian Institutes of Health Research (CIHR) New Investigator Award (Dr. Sareen), a Social Sciences and Humanities Research Council Canada Graduate Scholarship (J. Pagura), and the Canada Research Chairs program (Dr. Cox). Work on this study was funded in part by grants from the National Institute of Mental Health (K23-MH64736) and the National Institute on Drug Abuse (R01-DA20896) (Dr. Goodwin) and an operating grant from the CIHR (Dr. Cox). References [1] Goodwin RD, Jacobi F, Thefeld W. Mental disorders and asthma in the community. Arch Gen Psychiatry 2003;60:1125–30. [2] Goodwin RD, Fergusson DM, Horwood LJ. Asthma and depressive and anxiety disorders among young persons in the community. Psychol Med 2004;34:1465–74. [3] Committee TISoAaAiCIS. Worldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC. Lancet 1998;351:1225–32. [4] Prevention CfDCa. Measuring childhood asthma prevalence before and after the 1997 redesign of the National Health Interview Survey— United States. MMWR Morb Mortal Wkly Rep 2000;49:908–11. [5] Grant EN, Lyttle CS, Weiss KB. The relation of socioeconomic factors and racial/ethnic differences in US asthma mortality. Am J Public Health 2000;90:1923–5. [6] Feldman JM, Siddique MI, Morales E, Kaminski B, Lu S, Lehrer PM. Psychiatric disorders and asthma outcomes among high-risk inner-city patients. Psychosom Med 2005;67:989–96. [7] Stein MB, Cox BJ, Afifi TO, Belik S, Sareen J. Does comorbid depressive illness magnify the impact of physical illness? A population-based perspective. Psychol Med 2006;36:587–96. [8] Adams RJ, Wilson DH, Taylor AW, et al. Psychological factors and asthma quality of life: a population based study. Thorax 2004;59: 930–5. [9] Hilton L. Covering and cutting the high cost of asthma care. 2007. Accessed March 24, 2009. [10] Akinbami L. Asthma prevalence, health care use and mortality: United States, 2003–2005. 2006. Accessed March 24, 2009. [11] Murray CJL, Lopez AD. Alternative projections of mortality and disability by cause 1990–2020: Global Burden of Disease Study. Lancet 1997;349:1498–504. [12] Gravel R, Beland Y. The Canadian Community Health Survey: mental health and well-being. Can J Psychiatry 2005;50:573–9.
R.D. Goodwin et al. / Journal of Psychosomatic Research 68 (2010) 165–173 [13] Bailie L, Dufour J, Hamel M. Data quality assurance for the Canadian Community Health Survey, 2002. [14] American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: American Psychiatric Association, 2000. [15] Kessler RC, Wittchen HU, Abelson JM, et al. Methodological studies of the Composite International Diagnostic Interview (CIDI) in the US National Comorbidity Survey (NCS). Int J Methods Psychiatr Res 1998;7:33–55. [16] Wittchen HU. Reliability and validity studies of the WHO— Composite International Diagnostic Interview (CIDI): a critical review. J Psychiatr Res 1994;28:57–84. [17] Frayne SM, Seaver MR, Loveland S, et al. Burden of mental illness in women with depression and posttraumatic stress disorder. Arch Intern Med 2004;164:1306–12. [18] Sareen J, Cox BJ, Afifi TO, Clara I, Yu BN. Perceived need for mental health treatment in a nationally representative Canadian sample. Can J Psychiatry 2005;50:643–51. [19] Sareen J, Cox BJ, Afifi TO, Yu BN, Stein MB. Mental health service use in a nationally representative Canadian survey. Can J Psychiatry 2005;50:73–81. [20] Sareen J, Jagdeo A, Cox BJ, et al. Perceived barriers to mental health service utilization in the United States, Ontario, and the Netherlands. Psychiatr Serv 2007;58:357–64. [21] Sareen J, Jacobi F, Cox BJ, Belik SL, Clara I, Stein MB. Disability and poor quality of life associated with comorbid anxiety disorders and physical conditions. Arch Intern Med 2006;166:2109–16. [22] Shah BV, Barnswell BG, Bieler GS. SUDAAN user's manual: software for the analysis of correlated data. Release 6.40. Research Triangle Park (NC): Research Triangle Institute, 1995. [23] Goodwin RD, Fischer ME, Goldberg J. A twin study of post-traumatic stress disorder symptoms and asthma. Am J Respir Crit Care Med 2007;176:983–7.
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[24] Kean EM, Kelsay K, Wamboldt F, Wamboldt MZ. Posttraumatic stress in adolescents with asthma and their parents. J Am Acad Child Adolesc Psychiatry 2006;45:78–86. [25] Bussing R, Burket RC, Kelleher ET. Prevalence of anxiety disorders in a clinic-based sample of pediatric asthma patients. Psychosomatics 1996;37:108–15. [26] Bender B, Klinnert M. Psychological correlates of asthma severity and treatment outcome in children. In: Kotses H, Harver A, editors. Self management of asthma: lung biology in health and disease, Vol. 113. New York: Marcel Dekker, 1998. pp. 63–88. [27] Goodwin RD, Pine DS. Respiratory disease and panic attacks among adults in the United States. Chest 2002;122:645–50. [28] Goodwin RD, Eaton WW. Asthma and the risk of panic attacks among adults in the community. Psychol Med 2003;33:879–85. [29] Evans DL, Charney DS, Lewis L, et al. Mood disorders in the medically ill: scientific review and recommendations. Biol Psychiatry 2005;58:175–89. [30] Kessler RC, Ormel J, Demler O, Stang PE. Comorbid mental disorders account for the role impairment of commonly occurring chronic physical disorders: results from the National Comorbidity Survey. J Occup Environ Med 2003;45:1257–66. [31] Wang PS, Berglund P, Olfson M, Pincus HA, Wells KB, Kessler RC. Failure and delay in initial treatment contact after first onset of mental disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry 2005;62:603–13. [32] Goodwin RD, Chuang S, Simuro N, Davies M, Pine DS. Association between lung function and mental health problems among adults in the United States: findings from the First National Health and Nutrition Examination Survey. Am J Epidemiol 2007; 165:383–8. [33] McCauley E, Katon W, Russo J, Richardson L, Lozano P. Impact of anxiety and depression on functional impairment in adolescents with asthma. Gen Hosp Psychiatry 2007;29:214–22.
Asthma and mental disorders in Canada: Impact on functional impairment and mental health service use Renee D. Goodwin a,⁎, Jina Pagura b,d , Brian Cox b,c,d , Jitender Sareen b,c a
Mailman School of Public Health, Columbia University, New York, NY, USA b Department of Psychiatry, University of Manitoba Winnipeg, MB, Canada c Department of Community Health Science, University of Manitoba Winnipeg, MB, Canada d Department of Psychology, University of Manitoba Winnipeg, MB, Canada Received 23 April 2008; received in revised form 21 May 2009; accepted 16 June 2009
Abstract Objective: The goal of this study is to examine the association between asthma and mental disorders and the impact of asthma and mental disorder comorbidity on functional impairment and mental health care service use among adults in the community. Methods: Data came from the Canadian Community Health Survey Cycle 1.2 (N=36,984; age ≥15 years; response rate, 77%). Mental disorders were assessed using the Composite International Diagnostic Interview. Chronic physical health conditions, quality of life, and disability were also assessed. Asthma diagnoses were based on self-report of having been diagnosed with asthma by a health care professional. Results: Asthma was associated with a significantly increased likelihood of a range of mental disorders among adults in Canada, with the strongest links between asthma and posttraumatic stress disorder, mania, and panic disorder. Adults
with both mental disorders and asthma had significantly higher rates of functional impairment and use of mental health services, compared with those with either asthma or mental disorders but not both. Conclusions: Our findings provide new information suggesting that adults in the community with asthma and mental disorders have higher levels of both short- and long-term healthcondition-related functional disability and greater use of mental health services, compared with those with asthma without mental disorders. Results are also consistent with previous studies showing a significant link between asthma and mental disorders. Implications of these findings for efforts aimed at secondary prevention and improving treatment strategies for individuals with both asthma and mental disorders are discussed. © 2010 Published by Elsevier Inc.
Keywords: Asthma; Mental disorders; Chronic disease; Health service use; Epidemiology; Comorbidity
Introduction Several national studies have shown links between asthma and mental disorders [1,2]. Examining this problem in a range of geographic areas is important, as there is wide geographic variation in the prevalence of asthma [3,4]. There is also substantial geographic variation in the prevalence of potential causes and correlates of asthma [5]. Mounting data suggest that understanding these ⁎ Corresponding author. Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th Street, Rm. 1706, New York, NY 10032, USA. Tel.: +1 212 342 0422; fax: +1 212 342 5170. E-mail address: [email protected] (R.D. Goodwin). 0022-3999/09/$ – see front matter © 2010 Published by Elsevier Inc. doi:10.1016/j.jpsychores.2009.06.005
geographical disparities may be important not only for identifying possible causes of the asthma epidemic but also in identifying more effective asthma prevention and management strategies. No study to date has examined the relationship between asthma and mental disorders in a nationally representative sample in Canada. Growing evidence also suggests that the comorbidity of asthma and mental health problems may have a potentially significant impact on daily functioning and mental health care service use. For instance, one study by Feldman et al. [6] found that asthma patients with at least one mental disorder reported significantly higher levels of asthma symptoms, impairment in daily functioning, medication use, and emergency room (ER) treatment for
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asthma, compared to patients with asthma without psychiatric disorders. This study did not find any difference, however, in actual pulmonary function between patients with and without a mental disorder. Another recent study showed an association between comorbid anxiety and higher levels of functional impairment among adults with respiratory disease, compared with those without anxiety [7]. A study in Australia additionally found significant links between asthma and psychological distress and mental health problems among adults [8], yet no previous community-based study has investigated the relationship between comorbidity of asthma and mental disorders on functioning and health service use in a national sample in Canada. Both asthma and mental disorders are costly to both the individual and society. Asthma is responsible for US$4912 per patient in health care costs [9] and 10.1 million [10] missed work days per year while major depression is expected to be the single leading cause of disability worldwide by the year 2020 [11], while there is some evidence to suggest that comorbidity of asthma and mental disorders is associated with higher levels of impairment. As health care use and help-seeking behavior are often driven by impairment levels and other factors, beyond clinical pathology, it is conceivable that rates of service use are affected by comorbidity as well. The current study aims to fill several gaps in existing research. First, the study will examine the relationship between asthma and mental disorders in a large nationally representative sample of adults in Canada. Second, the study will investigate the relationship between mental disorders and impairment in short-term and long-term functioning in various domains among adults with asthma. Third, the study will examine the relationship between asthma, mental disorders, and level of health service use. Finally, the study will investigate the role of differences in demographic characteristics and comorbid physical health conditions within these associations. We hypothesize that asthma will be associated with higher levels of mental disorders and that having both asthma and mental disorders will be associated with greater functional impairment and health service use, compared with asthma alone. We also predict that differences in demographic characteristics and other comorbid health conditions will play a role in these relationships but will not fully explain these associations.
Methods Sample Data came from the public use files of a survey designed by Statistics Canada under the provisions set out in the federal Statistics Act, the Canadian Community Health Survey cycle 1.2 (CCHS 1.2; N=36,984; age 15
and older; response rate, 77%) [12]. The target population was persons living in private dwellings in the 10 Canadian provinces, excluding persons living in the three territories or in First Nations Communities and clientele of institutions. A multistage stratified cluster design was utilized to ensure that the sample would be representative of the Canadian general population. Trained lay interviewers who received additional training to increase their sensitivity to mental health issues conducted the interviews, in either English or French depending on the preference of the respondent, using the ComputerAssisted Personal Interviewing method. A detailed description of the method of selection for household interviews is reported elsewhere [13]. Measures Sociodemographics Sex, age, education, marital status, and household income were included in the analysis. Income quartiles were derived in the following way: lowest income, bUS$15,000 for one or two people in the household, bUS$20,000 for three or four people in the household, bUS$30,000 for five or more people in the household; lower middle income, US$15,000– 29,999 for one or two people in the household, US$20,000– 39,000 for three or four people in the household, US $30,000–59,999 for five or more people in the household; upper middle income, US$30,000–59,999 for one or two people in the household, US$40,000–79,999 for three or four people in the household, US$60,000–79,999 for five or more people in the household; highest income, NUS$60,000 for one or two people in the household, NUS$80,000 for three or more people in the household. Asthma Asthma was assessed in the CCHS 1.2 in the chronic health conditions section. Respondents were told “We are interested in long-term conditions which are expected to last or have already lasted 6 months or more and that have been diagnosed by a health professional.” Respondents were then asked “Do you have asthma?” Psychiatric disorders Lifetime and past-year diagnoses of major depression, mania, panic attacks, panic disorder, social phobia, and agoraphobia and past-year diagnoses of alcohol dependence and drug dependence were assessed using the World Health Organization Composite International Diagnostic Interview (CIDI), which generates diagnoses according to definitions in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) [14–16]. Only pastyear diagnoses of alcohol and drug dependence exist due to a skip error in the questionnaire that precluded assessment of lifetime symptoms for respondents who were asked the pastyear dependence questions. Posttraumatic stress disorder (PTSD) was assessed in the chronic conditions section of the
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survey. Respondents were asked whether they had been diagnosed with PTSD. As described above, this diagnosis was described as being diagnosed by a health care professional and lasting at least 6 months. This methodology is consistent with the previous work by Frayne et al. [17]. Past-2-week disability Past-2-week disability was assessed with four variables. Variables reflecting disability due to physical health problems and disability due to mental health problems were calculated by totaling the number of days in the past 2 weeks that the respondent was in bed for the entire day or for most of the day (due to physical health problems or mental health problems). Two additional items asked respondents whether, during the last 2 weeks, there were any days where they cut down on things they normally did because of illness or injury and any days where it took extra effort to perform to their usual level at work or at their other daily activities because of illness or injury. In line with the methodology used in previous work with the CCHS [7,18,19], these variables were dichotomized into 0 versus 1 or more days of disability since their distributions were skewed with the majority of respondents endorsing 0 days of disability. Long-term disability Respondents were asked if a long-term physical health condition, mental condition, or health problem had reduced the amount or kind of activity (1) “at home”, (2) “at school”, (3) “at work”, or (4) “in other activities, for example, transportation or leisure”. Additionally, respondents were asked whether they had any difficulty “hearing, seeing, communicating, walking, climbing stairs, bending, learning, or doing any similar activities”. For each item, response choices were (1) sometimes, (2) often, or (3) never. Due to the skewed distributions of these variables, with the great majority of the sample reporting “never” for all areas of functioning, respondents endorsing “never” for each area of functioning were categorized as “not limited”, while those endorsing limitation sometimes or often were categorized as “limited.” This methodology has been utilized in previous work with CCHS data sets [7,18,19]. Health service use Three variables were used as indices of health service use in the current study. The attainability of mental health services in Canada is similar across most provinces in that it does not limit number of visitations [20]. One item assessed hospitalization. Respondents were asked whether they had ever been hospitalized overnight or longer in any type of health care facility to receive help for problems with their emotions, mental health, or use of alcohol or drugs. Another reflected any use of the ER. Respondents indicating that they had ER contact with any health professional were categorized as having ER use in the past year. The third treatment index used in this study reflected use of antianxiety
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medication. Respondents were asked whether they had used any medication to decrease anxiety or nervousness in the past year. Physical health conditions As described above, long-term conditions that are expected to last or have already lasted 6 months or more and have been diagnosed by a health care professional were assessed in the chronic health conditions section. There were 21 chronic physical health conditions assessed. These include food allergies, other allergies, asthma, fibromyalgia, arthritis or rheumatism, back problems, high blood pressure, migraines, chronic bronchitis, emphysema or chronic obstructive pulmonary disease, diabetes, epilepsy, cancer, stomach or intestinal ulcers, stroke, bowel disorder, cataracts, glaucoma, thyroid condition, chronic fatigue syndrome, and multiple chemical sensitivities. Respondents' indications of the presence of each of these chronic conditions were used to create a dichotomous variable reflecting comorbidity of physical health conditions. Individuals who had zero or one chronic condition were categorized as not exhibiting comorbidity of physical health conditions while those who had two or more physical health conditions were categorized as exhibiting comorbidity of physical health conditions. Analytic strategy First, cross tabulations were used to examine the frequency and proportions of asthma among different categories of sociodemographic variables described above. Chi-square tests of association were also used to examine relationships between sociodemographic factors and the presence of asthma. Next, the association between mental disorders and asthma was assessed using logistic regression. Asthma was entered as an independent variable predicting the presence of each mental disorder in bivariate regressions. These regressions were then repeated after adjusting for sociodemographics [adjusted odds ratio (AOR)]. Functional limitations and service use were examined using logistic regression as well. First, variables reflecting the presence of asthma, the presence of any mental disorder, and the interaction between these two variables were entered as predictors for each functional limitation and service use variable after adjusting for demographic factors, to examine multiplicative effects. Second, to examine more specific, additive effects, a four-category variable based on the presence versus absence of asthma and mental disorders (1=neither asthma nor mental disorder; 2=asthma, no mental disorders; 3=any mental disorder, no asthma; and 4=asthma and any mental disorder) was entered as an independent variable predicting each functional limitation and service use variable after adjusting for demographics (AOR-1) and after adjusting for demographics and comorbidity of physical health conditions (AOR-2). The additional adjustment for comorbidity of physical health conditions was utilized to demonstrate that associations were specific to asthma instead
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of reflecting chronic physical conditions in general. Similar methodologies have been used to examine other indices of functioning and their relationships with mental and physical health in German [21] and Canadian [7] samples. Finally, associations between specific mental disorders and functional limitations and service use were examined among individuals with asthma. All mental disorders assessed were entered simultaneously in a model predicting each functional limitation and service use variable, after adjusting for demographics. For all analyses, appropriate statistical weights provided by Statistics Canada were applied to ensure that the data were representative of the general population. Taylor Series Linearization, a variance estimation procedure, was also used in all analyses to account for the complex sampling design of the survey [13]. This was conducted with SUDAAN software [22] using the statistical weight and stratification information within the CCHS 1.2 public use data set [13].
Results Sociodemographic characteristics associated with asthma among adults in Canada Among adults in Canada, asthma was more common among those who are younger, who are female, and who have never been married or are divorced (see Table 1). In
addition, asthma is more frequently found among adults with less formal education and lower income. All associations were significant at the Pb.001 level. Association between asthma and mental disorders All mental disorders were more common among adults with asthma, compared with those without asthma with the exception of past-year illicit drug dependence (see Table 2). Strong associations emerged between asthma and PTSD and between asthma and mania, followed by panic attacks and panic disorder. After adjusting for differences in demographic characteristics, these associations were attenuated slightly but remained statistically significant. Association between asthma and mental disorder comorbidity and functional limitations There was a significant interaction between asthma and the presence of any mental disorder for the outcome of 2week disability due to mental health and not for the other disability outcomes. In regressions using the four-category independent variable, having asthma or a mental disorder was associated with significantly increased impairment in past-week and impairment in long-term functioning after adjusting for sociodemographic factors (see Table 3). Adults with asthma and at least one mental disorder showed substantially higher levels of impairment compared with
Table 1 Sociodemographic characteristics associated with asthma among adults in Canada
Age (years) 15–24 25–44 45–64 65+ Gender Male Female Marital status Married/cohabit Separated/divorced/widowed Never married Education Up to 8th grade 9–13th grade High school graduate At least some post-secondary education Income Lowest Lower middle Upper middle Highest
Without asthma (n=33,622), n (%)
With asthma (n=3358), n (%)
χ2 (df)
4965 (15.99) a 11,657 (38.05) 9915 (30.96) 7085 (15.00)
708 (22.52) 1155 (37.90) 845 (25.63) 650 (13.95)
14.99 (3) ⁎⁎⁎
15,550 (49.93) 18,072 (50.07)
1222 (40.82) 2136 (59.18)
46.30 (1) ⁎⁎⁎
17,706 (62.52) 7166 (12.64) 8712 (24.84)
1476 (53.31) 791 (14.80) 1086 (31.89)
24.67 (2) ⁎⁎⁎
3329 (8.16) 6168 (16.93) 5949 (19.09) 17,974 (55.82)
375 (9.11) 720 (20.50) 548 (17.50) 1687 (52.89)
4.83 (3) ⁎⁎
4337 (9.84) 7330 (20.93) 10,829 (35.96) 8030 (33.27)
631 (14.44) 748 (20.91) 953 (33.87) 687 (30.78)
9.79 (3) ⁎⁎⁎
All n's are unweighted. All percentages are weighted. a Percentages can be interpreted as follows: 15.99% of respondents without asthma were 15–44 years old. ⁎⁎ P≤.01. ⁎⁎⁎ P≤.001.
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Table 2 Association between asthma and mental disorders among adults in Canada
Mental disorders Any mental disorder Major depression Manic episode Panic disorder Panic attack Social phobia Agoraphobia PTSD Past-year mental disorders Alcohol dependence Illicit drug dependence
Without asthma (n=33,622), n (%)
With asthma (n=3358), n (%)
Unadjusted OR (95% CI)
AOR (95% CI)
10,620 (31.52) a 4077 (11.69) 785 (2.18) 1175 (3.46) 6804 (19.81) 2683 (7.81) 489 (1.47) 384 (0.89)
1487 (44.07) 635 (17.92) 153 (4.43) 222 (6.29) 1014 (29.06) 376 (11.22) 78 (2.27) 94 (2.35)
1.71 (1.54–1.91) ⁎⁎⁎ 1.65 (1.43–1.90) ⁎⁎⁎ 2.08 (1.62–2.69) ⁎⁎⁎ 1.87 (1.51–2.33) ⁎⁎⁎ 1.66 (1.48–1.86) ⁎⁎⁎ 1.49 (1.26–1.76) ⁎⁎⁎ 1.56 (1.11–2.20) ⁎ 2.69 (1.97–3.66) ⁎⁎⁎
1.66 (1.48–1.86) ⁎⁎⁎ 1.61 (1.39–1.87) ⁎⁎⁎ 1.93 (1.47–2.53) ⁎⁎⁎ 1.73 (1.38–2.17) ⁎⁎⁎ 1.62 (1.43–1.83) ⁎⁎⁎ 1.45 (1.22–1.73) ⁎⁎⁎ 1.41 (0.98–2.03) 2.62 (1.89–3.63) ⁎⁎⁎
923 (2.48) 250 (0.75)
124 (3.63) 38 (1.04)
1.48 (1.16–1.90) ⁎⁎ 1.38 (0.89–2.15)
1.29 (0.98–1.71) 1.36 (0.86–2.15)
All n's are unweighted. All percentages are weighted. AOR=adjusted for gender, age, education, income, and marital status. a Percentages can be interpreted as follows: 31.52% of respondents without asthma had any mental disorder. ⁎ P≤.05. ⁎⁎ P≤.01. ⁎⁎⁎ P≤.001.
individuals either with asthma and no mental disorders or with a mental disorder but no asthma. Additionally, having both asthma and mental disorders was also associated with significantly higher rates of recent work loss due to both physical and mental health. After adjusting for differences in demographic characteristics as well as comorbidity of physical health conditions, the link between comorbid asthma and mental disorders and increased rates of functional impairment remained strong and statistically significant (see Table 3), compared with limitations among those with asthma and no mental disorder. In contrast, most odds ratios were no longer significant after these adjustments when compared to individuals with a mental disorder and no asthma. Individuals with a mental disorder only were significantly more likely than individuals with asthma only to exhibit functional limitations in all domains, with the exception of functional limitations at school, after adjusting for both sociodemographics and comorbidity of physical health conditions. More specifically, among adults with asthma, major depressive episode and social phobia were associated with significantly increased odds needing extra effort to perform at usual level, limitation in normal activities, and limited activity in home and school. Panic disorder was also associated with limitation in normal activities and limited activities at home, work, and other domains. No other mental disorders, with the exception of a link between drug dependence and extra effort needed to perform at usual level, were found between specific mental disorders and functional limitations (results not presented). Association between asthma and mental disorder comorbidity and mental health service use There was a significant interaction between asthma and the presence of any mental disorder for the outcome of any ER contact. There were no other significant interactions for
health service use outcomes. In regressions using the fourcategory independent variable, having both asthma and mental disorders was associated with significantly higher rates of overnight hospitalization and use of antianxiety medication in comparison to those with mental disorders without asthma or those with asthma without a mental disorder (see Table 4). Individuals with a mental disorder only were significantly more likely than individuals with asthma only to report being hospitalized overnight or longer and taking antianxiety medication after adjusting for both sociodemographics and comorbidity of physical health condition. More specifically, among adults with asthma, major depressive episode, mania, panic disorder, social phobia, and agoraphobia were associated with increased odds of overnight hospitalization; social phobia and agoraphobia were associated with any ER use; and major depressive episode, panic disorder, and social phobia were associated with use of antianxiety medication (results not presented).
Discussion The four main findings of this study will be summarized, considered in the context of previously available data, and then discussed in terms of their implications for future research. First, we found that asthma is associated with a significantly increased likelihood of a range of mental disorders among adults in Canada. Second, we found that having both asthma and mental disorders was associated with significantly higher levels of functional impairment and limitations in functioning, compared with asthma alone. Third, results showed that having both asthma and mental disorders was associated with significantly higher levels of mental health service use, compared with use among adults with mental disorders without asthma. Fourth, our results
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Table 3 Association between asthma and mental disorder comorbidity and functional limitations in Canada Asthma and mental disorder group compared to mental-disorder-only group
n (%)
AOR-1 (95% CI)
82 (0.33) a
n (%)
n (%)
n (%)
AOR-1 (95% CI)
AOR-2 (95% CI)
29.08 (8.94–94.63) ⁎⁎⁎ 27.47 (8.44–89.42) ⁎⁎⁎ 1.76 (1.22–2.53) ⁎⁎⁎ 1.21 (0.83–1.76)
4 (0.12)
302 (2.31)
84 (4.06)
2343 (9.92)
300 (14.14)
1824 (16.30)
386 (25.40)
2.17 (1.68–2.81) ⁎⁎⁎
2.03 (1.57–2.63) ⁎⁎⁎
1.79 (1.46–2.18) ⁎⁎⁎ 1.17 (0.95–1.44)
2096 (8.92)
270 (12.84)
1876 (16.35)
393 (25.45)
2.44 (1.87–3.17) ⁎⁎⁎
2.28 (1.75–2.96) ⁎⁎⁎
1.78 (1.45–2.17) ⁎⁎⁎ 1.16 (0.94–1.42)
2083 (8.60)
304 (14.09)
2098 (18.19)
430 (28.30)
2.57 (2.00–3.31) ⁎⁎⁎
2.40 (1.86–3.09) ⁎⁎⁎
1.84 (1.52–2.24) ⁎⁎⁎ 1.20 (0.99–1.46)
5587 (20.21)
651 (31.21)
3178 (27.26)
662 (42.82)
2.13 (1.68–2.69) ⁎⁎⁎
1.92 (1.52–2.42) ⁎⁎⁎
2.32 (1.94–2.78) ⁎⁎⁎ 1.36 (1.14–1.64) ⁎⁎⁎
3539 (12.47)
514 (25.56)
2505 (20.30)
582 (36.42)
2.23 (1.74–2.88) ⁎⁎⁎
1.96 (1.53–2.50) ⁎⁎⁎
2.70 (2.24–3.26) ⁎⁎⁎ 1.47 (1.22–1.78) ⁎⁎⁎
146 (3.63)
29 (11.71)
213 (11.45)
54 (19.42)
1.37 (0.64–2.94)
1.22 (0.56–2.67)
1.75 (1.03–2.97) ⁎⁎⁎ 0.89 (0.49–1.61)
1118 (7.39)
156 (15.50)
1232 (15.56)
257 (27.44)
2.26 (1.59–3.22) ⁎⁎⁎
2.08 (1.46–2.97) ⁎⁎⁎
2.38 (1.87–3.03) ⁎⁎⁎ 1.23 (0.96–1.57)
3382 (12.53)
480 (24.75)
2540 (21.82)
559 (35.01)
1.91 (1.49–2.46) ⁎⁎⁎
1.70 (1.33–2.16) ⁎⁎⁎
2.11 (1.75–2.54) ⁎⁎⁎ 1.18 (0.98–1.41)
All n's are unweighted. All percentages are weighted. AOR-1=adjusted for gender, age, education, income, and marital status. AOR-2=adjusted for gender, age, education, income, marital status, and comorbidity of physical health conditions (dichotomous one or no disorder vs. two or more disorders). a
AOR-2 (95% CI)
Percentages can be interpreted as follows: 0.33% of respondents with neither asthma nor any mental disorder had 2-week disability due to mental health. ⁎⁎⁎ P≤.001.
R.D. Goodwin et al. / Journal of Psychosomatic Research 68 (2010) 165–173
Past-2-week disability Two-week disability due to mental health Two-week disability due to physical health Cut down on things normally done Took extra effort to perform at usual level Long-term disability Limited in normal activities Limited in amount or kind of activity at home Limited in amount or kind of activity at school Limited in amount or kind of activity at work Limited in amount or kind of activity in other activities
Without asthma or With asthma but With mental disorder With asthma and mental disorder without mental but without asthma mental disorder Asthma and mental disorder group (n=22,172) disorder (n=1786) (n=10,620) (n=1487) compared to asthma-only group
a Percentages can be interpreted as follows: 1.80% of respondents with neither asthma nor any mental disorder had been hospitalized overnight or longer. ⁎⁎⁎ P≤.001.
10 (0.03) 704 (2.45)
485 (1.80)
Hospitalized overnight or longer Any ER use Antianxiety medication
All n's are unweighted. All percentages are weighted. AOR-1=adjusted for gender, age, education, income, and marital status. AOR-2=adjusted for gender, age, education, income, marital status, and comorbidity of physical health conditions (dichotomous one or no disorder vs. two or more disorders).
1.56 (0.53–4.58) 1.24 (0.98–1.56) – 5.05 (3.52–7.23) ⁎⁎⁎ 11 (0.69) 274 (17.09) 54 (0.39) 1307 (10.95) 0 (0.00) 84 (3.96)
62 (2.16)
1394 (10.71)
269 (14.60)
– 5.46 (3.80–7.84) ⁎⁎⁎
1.54 (0.57–4.17) 1.70 (1.35–2.14) ⁎⁎⁎
AOR-2 (95% CI)
1.10 (0.88–1.37) 1.36 (1.10–1.69) ⁎⁎⁎ 7.99 (5.13–12.44) ⁎⁎⁎ 8.40 (5.40–13.08) ⁎⁎⁎
AOR-1 (95% CI) AOR-2 (95% CI) AOR-1 (95% CI) n (%) n (%) n (%)
a
n (%) Services
With asthma and mental disorder (n=1487) With mental disorder but without asthma (n=10,620) With asthma but without mental disorder (n=1786) Without asthma or mental disorder (n=22,172)
Table 4 Association between asthma and mental disorder comorbidity and health service use among adults in Canada
Asthma and mental disorder group compared to asthma-only group
Asthma and mental disorder group compared to mental-disorder-only group
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indicated that demographic characteristics did not explain the observed links between asthma, mental disorders, and functional impairment among adults in Canada. Our findings on the relationship between asthma and mental disorders are remarkably consistent with previous community-based results from Germany [1] and New Zealand [2] both in terms of the overall strength of the associations between asthma and mental disorders (i.e., strength of the odds ratio) and in terms of the relative strength of the relationships between asthma and each of the mental disorders assessed. We found the strongest link between asthma and PTSD, although this association cannot be directly compared with either previous study as they did not assess PTSD. In addition, PTSD was not assessed with the CIDI in this study as were the other mental disorders; hence, the accuracy of this diagnosis is somewhat unclear. No previous community-based study has examined the relationship between asthma and PTSD, though results from recent twin [23] and clinical studies have suggested strong links possibly due to traumatic or life-threatening medical situations among those with asthma [24–26]. Consistent with previous population-based and clinical findings, there were also strong links between asthma and panic disorder and panic attacks [1,2,27,28]. Our results provide new data on the potential impact of having both asthma and mental disorders on functional impairment among adults in the community. These findings are consistent with previous results from primary care and community studies showing depression and other mental disorders associated with increased functional impairment among adults with diabetes and other physical health problems [29,30]. Although this is purely speculative since mental disorders are measured only by lifetime status, the finding that there is only a significant interaction between asthma and mental disorders in predicting impairment in the past 2 weeks is intriguing and has potential clinical implications suggesting that the comorbidity does indeed have a detrimental impact above and beyond that of either disorder independently. It may also be that temporality is critical to the impact this comorbidity has; the specificity of the finding to past-2-week impairment may reflect that both need to occur simultaneously for the impact to be evident and that, therefore, this is best reflected in the most recent time assessment. The possibility that temporality of the comorbidity of asthma and mental disorders may affect the related impairment/severity of disease is consistent with findings from the German study that found stronger associations between more severe asthma and past-year, compared with lifetime, mental disorders [1]. The potential conclusion that having both asthma and mental disorders concurrently, rather than comorbid during the lifetime but not at the same point in time, makes clinical sense from the perspective that coping with more than one disease concurrently would translate into greater impairment. It is further conceivable that, for instance, there may be an interaction between mental disorders and asthma on
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respiratory functioning, which could lead to greater impairment in several areas. Future studies that can more specifically examine these patterns with longitudinal data, more detailed description of types of impairment, and refined respiratory measures may be helpful in developing treatment strategies for patients with both conditions. Of particular interest, these findings suggest that having both asthma and mental disorders is associated with a significantly increased level of use of mental health services among adults, compared with those with mental disorders without asthma. It is not clear why this would be the case. It also seems as if much of this difference in use is explained by differences in demographic characteristics between those with mental disorders with asthma and those without. Previous clinical studies have specifically shown that asthma patients with use of mental disorders used higher levels of asthma medications, and asthma services, compared with asthma patients without mental disorders [31], though no previous study has demonstrated a link with mental health services. Limitations of this study should be considered when interpreting results. First, asthma diagnosis was by selfreport and we have no information on duration, age of onset, or severity. In addition, we did not have information on treatment or pulmonary function, although results of a community-based study that measured pulmonary function, which found links between respiratory disease and mental health, are consistent with these findings [32]. Second, asthma and mental disorders tend to be strongly associated with sociodemographic characteristics, and the level of variability of sociodemographic characteristics in Canada may differ from other communities, such as the United States, and therefore, replication may be useful in a variety of communities in order to understand the role of sociodemographic characteristics in these links. Third, as these data are cross-sectional, it was not possible to draw any causal conclusions. Fourth, methods available for diagnosing PTSD were limited, and additional studies replicating these findings using more commonly used standardized measures will be useful. Lack of information on smoking status is also a shortcoming of the study, since smoking can be related to both asthma-like symptoms and mental disorders, resulting in the possible overestimation of the results. In sum, these results replicate findings of a link between mental disorders and asthma among adults in the community, as has previously been observed in other countries. Our findings provide initial evidence suggesting that comorbidity of asthma and mental disorders is associated with increased functional impairment, compared with either disorder alone with some evidence of an interactive effect. Results also suggest that having both asthma and mental disorders appears to be associated with higher levels of mental health service use. We also found that specific mental disorders, most commonly major depression, panic disorder, and social phobia, were most strongly associated
with impairment and service use among adults with asthma, while other mental disorders had variable or nonsignificant effects. The impact of this comorbidity on impairment and service use provides evidence supporting the call to develop both screening measures for mental disorders among patients with asthma and to develop treatment strategies specific to addressing these problems when they co-occur [33]. Future clinical and epidemiologic studies that can begin to investigate these new strategies are needed. In addition, future investigations using longitudinal, prospective data to investigate these links may be informative into understanding the etiology of this pattern of comorbidity.
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