Lindström, Irmeli MD; Suojalehto, Hille MD; Pallasaho, Paula MD, PhD; Luukkonen, Ritva PhD; Karjalainen, Jouko MD, PhD; Lauerma, Antti MD, PhD; Karjalainen, Antti MD, PhD
Asthma is a significant, increasing health problem among working-age people.1,2 Recognizing the modifiable risk factors of poor asthma outcome is important for decreasing the burden of the disease. The impact of work and workplace exposure on asthma has been widely studied. Previous population-based studies have shown that job changes because of respiratory problems at work are common and that occupational exposure to irritants and dusts contribute to respiratory work disability.3 In earlier studies, about 20% of working asthmatic persons reported exacerbation of asthma symptoms at work.4,5 Exposure to occupational asthmogens has been associated with more severe adult-onset asthma,6 and work-related exposure to gas, dust, and fumes with multisymptom asthma7 and severe asthma exacerbations.8
Nevertheless, only limited information is available about the interactions of work and asthma since childhood or early adulthood. Childhood asthma is usually of an atopic phenotype and is generally milder than nonatopic adult-onset asthma.9 Men with asthma from a young age suffer from the disease throughout or almost throughout their entire career. Being male, they fairly often work in dusty environments. Therefore, more knowledge about how work and workplace exposure affect asthma that has begun at a young age is needed for improving guidance in the choice of profession among young asthmatic men.
Current asthma treatment can reduce asthma symptoms and possibly modify the effect of occupational exposure. This study was performed in Finland, where inhaled corticosteroids have been extensively used as a first-line therapy for persistent asthma for the last 20 years, and treatment practices have been influenced by the National Asthma Programme.10 Vocational guidance is mostly provided by the physicians treating asthmatic people. The Finnish Allergy Program11 encourages young people with severe asthma to avoid occupations with exposure to respiratory irritants; but generally, work as a firefighter is the only explicit career restriction to those with mild asthma. In Finland, occupational hygiene standards are considered high in general, and Finnish legislation requires that employers provide personal protective equipment for employees who are exposed to airborne harmful agents. Nevertheless, compliance with the use of such equipment varies.
The aim was to study the current occupational status and exposures and their associations with current asthma severity, asthma control, and the occurrence of exacerbations, in a population of approximately 40-year-old men with either mild or moderate asthma or relatively severe asthma in their youth.
Study Population and Design
The selection of study participants from the Finnish Defence Force register is explained in more detail in our previous study.12 In Finland, it is obligatory for all young men of sufficiently good health to participate in either military or civil service. At the end of the 1980s, about 90% of young men, typically at the age of 19 to 21 years, carried out 8 to 11 months of military service. Up to 98% of all men underwent a medical examination at the age of 18 to 19 years. Men with mild asthma and normal lung function were evaluated as fit for most service duties. Those with stable moderate asthma and good lung function were evaluated as fit for restricted duties. Men with unstable or deteriorating asthma or clearly decreased lung function were exempted from military service. We used the data for this classification when evaluating the severity of asthma at baseline.
The study consisted of two groups of asthmatic people and a control group without asthma. All participants were 39 to 44 years old at the time of the study. Asthma group 1 (N = 505) consisted of all men who were referred during 1987 to 1990 to the Central Military Hospital because of a diagnosis of asthma (including men in military service with asthma already diagnosed before service and men with a new onset of asthma during service). This group represented an unselected population of men who suffered from mild or moderate asthma and lived in southern and central parts of Finland during their military service at the age of 18 to 27 years. Asthma group 2 (N = 393) included men who were exempted from military service in 1986 to 1989 because of asthma, representing an unselected population of Finnish men suffering from relatively severe asthma at the age of 18 years.
The control group (N = 1500) was randomly selected from the 7433 young men who entered military service in five big military units in southern Finland between 1986 and 1990 and who had no asthma diagnosis during military service according to the Defence Force register. After the completion of the study, we excluded the 28 men who, in the study questionnaire, reported having been diagnosed with asthma during their military service. We decided to select 1500 controls to ensure a sufficient number with regard to probable nonresponse and in relation to the number of asthma cases. About 90% of the population of young men served their military service at the end of the 1980s. The selected five military units were located in different areas of southern Finland; and to avoid any selection bias, all nonasthmatic men entering service in those units in 1986 to 1990 were chosen for randomization. Thus, the controls represented an unselected population of men without asthma or any other disabling illness in their youth and who lived in southern or central parts of Finland.
A postal questionnaire was sent out in the spring of 2009, that is, approximately 20 years (18 to 23 years) after military service or exemption at call up. After two reminders, 232 men (54%) from the first study group, 161 (44%) from the second study group, and 608 (44%) of the controls answered and thus composed the final study population.
We used the nationwide registers of the Finnish Social Insurance Institution to obtain information on the nonrespondents. We collected the following data on both asthma groups' respondents and nonrespondents: (1) special medication reimbursement rights for asthma medication in 1992 and 2009 (objective data on reversible bronchial obstruction and the typical symptoms of persistent asthma must be demonstrated to obtain the reimbursement rights; see Saarinen et al4 for details of the definition and criteria of these rights), (2) asthma medication purchases in 2008, (3) the number of sick leave periods because of respiratory illness lasting more than 9 days in 2009. The study was approved by the ethical committee of the Department of Medicine of the Helsinki University Central Hospital, and the study participants gave their written informed consent.
The questionnaire included questions on personal characteristics, education, lifetime work history, current exposures at work, relief of asthma symptoms during days off, work ability, lifestyle, weight, and height. We used the previously validated Finnish questions of the Tuohilampi questionnaire13 to evaluate current asthma symptoms, the presence of other atopic disorders, the current use of asthma medication, and the age of asthma onset. For this study, the data were assessed as follows.
We used the Asthma Control Test™ to evaluate current asthma control14 (Finnish version of the Asthma Control Test™. The Asthma Control Test™ is a trademark of Quality Metric Incorporated © 2002 GlaxoSmithKline). This self-administered questionnaire assesses the key components of asthma control over the preceding 4 weeks, including asthma symptoms, everyday functioning, the use of rescue medications, and night-time awakenings. The Asthma Control Test™ scale ranges from 5 to 25, with higher scores indicating better asthma control. Men with scores less than 20 are identified as having poorly controlled asthma.
The participants were classified as having asthma exacerbation if they reported at least one of the following during the past 12 months: (1) an unscheduled visit to a physician or a visit to the emergency department for asthma, (2) hospitalization for asthma, or (3) an oral corticosteroid burst for asthma.
A chest physician (Irmeli Lindström) estimated the current severity of asthma according to the information on asthma medication used, asthma symptoms, night-time symptoms, and their frequency during the last 12 months. The classification was based on the modified Global Initiative for Asthma guidelines,15 without forced expiratory volume in 1 second values, as in previous studies.16 The categories were as follows: remission, intermittent, mild persistent, moderate persistent, and severe persistent. Remission was defined as having had no asthma symptoms and not having used asthma medication in the last 3 years. In the risk factor analyses, we compared the men with asthma in remission, intermittent asthma, or mild persistent asthma categories with those with moderate or severe persistent asthma.
Occupational Exposure Assessment
The participants who were not currently employed (22 men in asthma group 1, 23 men in asthma group 2, and 49 controls) were excluded from the analyses of occupational exposure (Tables 1 and 2). Because asthma exacerbations and severity were evaluated over the preceding 12 months, participants who had changed jobs in 2008 or 2009 were excluded when occupational exposure was studied as a determinant of poor asthma outcome (22 men in asthma group 1 and 14 men in asthma group 2; Table 2).
The respondents were asked about exposure to each of the following factors in their current job, using previously established questions: dusts, chemical agents or factors, abnormal temperatures (cold and heat), poor indoor air quality, and physically strenuous work.4
The current occupation of the respondents was first coded according to the 1997 Classification of Occupations of Statistics Finland,17 which is based on ISCO-88 (COM), the European Community version of the International Standard Classification of Occupations. The coded occupational history was matched with the asthma-specific job exposure matrix (JEM) developed by Kennedy et al.18 The study participants were assigned to exposure risk groups on the basis of currently having a job that places them at high risk of developing occupational asthma or being exposed to some nonspecific respiratory irritants. The asthmogens were classified into three groups as follows: high-molecular-weight agents, low-molecular-weight agents, or mixed environment; the nonasthmogenic irritants were classified into one separate group, as in the previous study.6 We ignored latex exposure in this study, as nonpowdered low-latex gloves have been used in Finland for many years.
Other Explanatory Variables
Smoking: On the basis of the questionnaire data, the respondents were classified as current smokers, ex-smokers, or nonsmokers.
Body mass index (BMI) was calculated as weight in kilograms divided by the square of height in meters, from self-reported measures at follow-up. Obesity was defined as having a BMI of 30 kg/m2 or more.
Education: Men having completed only comprehensive school, high school, or vocational school were classified as having basic education. Those with college or other upper secondary education were classified as having mid-level education. Men with a university degree were classified accordingly.
Professional status was categorized as upper-level nonmanual worker, lower-level nonmanual worker, manual worker, self-employed (including farmers), not currently employed, and other or unknown. In the risk factor analyses, upper- and lower-level nonmanual workers were classified as nonmanual workers.
Men who answered “yes, frequently” or “yes, sometimes” to the question: Do your asthma symptoms decrease on days off (“no symptoms in current job” or “yes, frequently” or “yes, sometimes” or “no”) was defined as having relief from asthma symptoms on days off. In the risk factor analyses, these men were compared with those choosing the last answer alternative (no). Information was elicited on whether or not men had changed occupation after military service and whether asthma was the reason for the change (“no” or “yes, partly” or “yes, mainly”).
Our data set consisted of both continuous and categorical variables. We tested whether the asthma groups and their controls differed from each other and applied chi-square tests for categorical variables and one-way analysis of variance for continuous variables. A P value of less than 0.05 was considered statistically significant.
We used logistic regression analyses for examining the associations between determinants at follow-up and poorly controlled asthma, asthma exacerbations, and current asthma severity. The odds ratios (ORs) with 95% confidence intervals (95% CI) are presented. All analyses were carried out using the Statistical Analysis System 9.1 program (SAS Institute, Cary, NC).
Characteristics of Study Populations
The characteristics of the study groups are presented in Table 1. The socioeconomic status of asthma group 2 differed from the other groups: these men were less educated, more often manual workers, and a larger proportion of them were not currently employed. Interestingly, 30.8% (n = 4) of the not currently employed men in asthma group 1 (n = 13) and 56.2% (n = 9) of the not currently employed men in asthma group 2 (n = 16) reported being partly or mainly unemployed because of asthma.
There was no significant difference in self-reported occupational exposures in current work between the groups. According to the JEM, exposure to low-molecular-weight asthmogens in current work was more common among the controls (P = 0.006), but we found no significant difference in exposure to other asthmogens or nonasthmogenic irritants between the study groups. Change of occupation because of asthma was relatively uncommon, being reported by only 13.8% of the men in asthma group 1 and 16.8% of the men in asthma group 2.
Comparison of Respondents and Nonrespondents
The respondents of asthma group 2 had special medication reimbursement rights for asthma medication statistically significantly more often in 1992 (P = 0.022) and in 2009 (P = 0.007) compared with nonrespondents (Table 2). We found no other significant differences between the respondents and nonrespondents.
Current Asthma Status
Asthma was more often poorly controlled in asthma group 2 than in asthma group 1 (28.0% vs 15.1%; P = 0.002; Table 3), and exacerbations during the past 12 months were more frequent (19.3% vs 11.6%; P = 0.036). A total of 40.5% of the men in asthma group 2 and 17.7% of the men in asthma group 1 (P = <0.001) currently had moderate or severe persistent asthma.
Determinants of Current Poor Asthma Outcome
In the univariate model (data not shown), current smoking associated with poorly controlled asthma in asthma group 1 (OR = 3.6; 95% CI, 1.4 to 9.3) and in asthma group 2 (OR = 2.5; 95% CI, 1.1 to 5.5), whereas asthma exacerbations did not significantly associate with smoking in either groups. The determinants of having poorly controlled asthma and the occurrence of exacerbations during the last 12 months are presented in Table 4. In this model, asthma group 1 (men with mild or moderate asthma in youth) and asthma group 2 (men with relatively severe asthma in youth) are analyzed separately by using logistic regression, including adjustment for smoking status (current smoker vs ex- or nonsmoker).
Poorly Controlled Asthma
Being obese (OR = 4.2; 95% CI, 1.2 to 14.9) associated significantly with poorly controlled asthma in asthma group 1. Not being currently employed yielded an OR of 3.5 (95% CI, 1.1 to 11.0), and relief of asthma symptoms on days off an OR of 2.4 (95% CI, 1.0 to 5.7), for currently poorly controlled asthma in asthma group 2.
Occurrence of Exacerbation During Last 12 Months
In both the asthma groups, reported relief of asthma symptoms on days off associated with asthma exacerbations (OR = 3.0; 95% CI, 1.0 to 9.2 in asthma group 1; and OR = 3.2; 95% CI, 1.2 to 8.5 in asthma group 2). Having only basic education showed a tendency to associate with exacerbations but without statistical significance. In asthma group 2, being a manual worker or self-employed (OR = 4.5; 95% CI, 1.2 to 16.3) and not being currently employed (OR = 4.9; 95% CI, 1.1 to 22.3) associated significantly with asthma exacerbations. Self-reported occupational exposure to dust or chemical agents or gases or fumes, abnormal temperatures, and bad indoor air quality as well as physically strenuous work showed a clear tendency to associate with exacerbations in asthma group 2, with ORs between 2.0 and 3.5. Nevertheless, they had no statistical significance. We also detected some tendency of association between the JEM-based exposure to nonasthmogenic irritants and asthma exacerbations, as well as poorly controlled asthma in asthma group 2.
Moderate or Severe Persistent Asthma
We also analyzed associations between current moderate or severe persistent asthma and all the listed variables in Table 4 (data not shown). We found no significant associations.
We studied the current occupational exposure and its association with current poor asthma outcome in men aged approximately 40 years with asthma since childhood or early adulthood. The self-reported and expert-evaluated current occupational exposure to asthma-aggravating factors differed only slightly between the asthmatic groups and the controls without asthma in youth. In men with relatively severe asthma in youth (asthma group 2), (1) being a manual worker or self-employed associated significantly with asthma exacerbations, (2) self-reported occupational exposure to asthma-aggravating factors showed a clear tendency to associate with asthma exacerbations, and (3) not being currently employed and days off, providing relief from asthma symptoms, associated with asthma exacerbations and poorly controlled asthma. In men with mild or moderate asthma in their youth (asthma group 1), current professional status and exposure had less effect on current asthma status.
In this study, asthma that had started at a young age seemed to have only a small effect on current occupation and exposure to airway irritants, when a participant was 40 years old. Dumas et al19 reported that the participants with more severe asthma in childhood tended to choose less exposing jobs. In a US adult population–based study, those with childhood asthma history generally achieved a better educational level and tended to work in specific jobs.20 Nevertheless, in a Swedish conscription register–based study, asthma diagnosis in adolescence only marginally influenced the choice of job.21
In our final model, asthma exacerbations in men with relatively severe asthma in youth were associated with being a manual worker or being self-employed, whereas self-reported or JEM-based occupational exposure showed only a tendency to associate with asthma exacerbations. In this model, variables were adjusted only for smoking, because all study participants were male and of the same age and BMI showed no association with asthma exacerbations. In addition, occupational exposure–related variables correlated closely with each other and with the educational level. In the European Community Respiratory Health Survey, the relative risk for severe asthma exacerbation during the last year was 3.1 in participants with JEM-based occupational exposure to dust, gas, or fumes.8 This association, which was stronger than that of our results, can be explained by the fact that the European Community Respiratory Health Survey included women and participants with adult-onset of asthma, and also by the use of a different JEM.
In this study, current occupational exposure did not correlate with asthma severity, as has been reported in the European study of severe asthma.22 The study of Le Moual et al6 did not detect an association between severe asthma and the exposure to occupational asthmogens or irritants among participants with childhood-onset asthma, although a positive association was found among participants with adult-onset of the disease. In a Swedish study, occupational exposure to gas dust or fumes yielded an OR of 2.0 for multisymptom asthma, which could be used as a marker of more severe asthma.7 Smoking and obesity associated with poorly controlled asthma in our study, as has also been shown earlier.23,24
The study population in this survey was homogenous regarding age and sex and represented unselected men from southern and central parts of Finland. The asthma groups had a clinically verified disease at the age of 19 to 21 years and represented all severity forms of asthma, and their asthma severity in youth could be evaluated. The controls had not suffered from asthma in their youth. This setting allowed us to study the associations between work-related exposures and asthma in middle-aged men with asthma for at least 20 years. Because of the extensive use of inhaled corticosteroids in Finland during the follow-up period,10 it is probable that the associations also apply to young men whose asthma is treated according to the current recommendations.25 We used several clinically relevant outcomes to evaluate current asthma status and used both self-reported and JEM-based information on occupational exposure.
Because of the rather low response rate, the selection of a specific type of asthmatic people cannot be ruled out. Nevertheless, the register-based information on asthma medication and sick leaves showed only relatively small differences between the respondents and the nonrespondents. In addition, a Swedish study with a male response rate of 56% found no difference in respiratory symptoms between respondents and nonrespondents.26 Second, the healthy worker effect might have led to an underestimation of associations between occupational exposures and asthma. Nevertheless, in this study, current occupational exposure to asthma-aggravating factors differed only slightly between the asthmatic groups and the controls, and change of occupation because of asthma was relatively uncommon in both the asthma groups. On the basis of these facts, it seems unlikely that a significant proportion of asthmatic people would have chosen cleaner jobs. In this study, occupational exposure to asthma-aggravating factors only showed a trend with no statistical significance, which could be explained by the small number of study participants. The true association between occupational exposure and poor asthma outcome is supported by the fact that being a manual worker or being self-employed was also a clear risk factor for asthma exacerbations.
Findings from this population-based longitudinal study suggest that current work and occupational exposure may associate with the occurrence of asthma exacerbations in middle-aged men who have had relatively severe asthma at around 20 years of age. Nevertheless, the role of current workplace exposure on asthma seems to be less significant among young men with milder asthma. On the basis of our findings, it is advisable to take asthma severity into account in the vocational guidance of young asthmatic men. It seems unjustified to guide those with a relatively mild form of the disease to restrict their careers. Nevertheless, paying attention to the choice of future work environment and avoidance of exposure to respiratory irritants may be relevant for young men with a more severe form of asthma. These conclusions are in line with the current recommendation of the Finnish Allergy Program.
Occupational health care professionals should frequently assess asthmatic men who are already working and are exposed through their work to respiratory irritants, abnormal temperatures, or physically strenuous tasks. Employers should consider reducing occupational exposure to asthma-aggravating factors and motivating employees with relatively severe asthma since youth to regularly use personal protective equipment, especially if frequent exacerbations occur or asthma control is poor.
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