Article Text
Abstract
Objectives Occupational exposure to the composite measure vapours, gases, dusts and fumes (VGDF), contribute to the burden of asthma and rhinitis. The objective was to evaluate occupational exposure to VGDF, which is further divided into the components chemicals, organic and inorganic dust in relation to asthma and rhinitis.
Methods Previously examined participants from three population-based cohorts in the Obstructive Lung disease In Northern Sweden (OLIN) studies were re-examined during 2002–2004. In total, 4036 participated in a structured interview and answered a questionnaire on occupational exposures.
Results Occupational exposure to VGDF increased the risk of asthma, and concomitant asthma and rhinitis. Exposure to chemicals, but not dust, showed a similar pattern. Exposure to chemicals increased the risks (OR, 95% CI) of rhinitis without asthma (1.29, 1.10 to 1.52), asthma without rhinitis (1.42, 1.15 to 1.77) and concomitant asthma and rhinitis (1.60, 1.31 to 1.96) when adjusted for confounders such as age, smoking habits, body mass index and sex. The association between exposure to chemicals and asthma and rhinitis remained independent of exposure to dust and was also so when excluding exposure to isocyanates and welding fumes. The results were similar for women and men, as well as for never-smokers and participants without a history of allergy.
Conclusions In this cross-sectional population-based study, occupational exposure to chemicals contributed substantially to the increased risk of asthma and rhinitis observed for occupational exposure to VGDF.
- Materials
- exposures and occupational groups
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What this paper adds
Occupational exposure to vapours, gases, dusts and fumes (VGDF) is associated with asthma and rhinitis, but it is unclear to what extent the different components explain the observed association.
We found that occupational exposure to chemicals, but not inorganic or organic dust, was the main contributing factor for the observed increased risks of asthma and rhinitis among participants exposed to VGDF.
The results suggest that an increased vigilance regarding occupational exposure to chemicals may have a beneficial effect on respiratory health in the population.
Introduction
Asthma and rhinitis are common occupational airway disorders,1 ,2 and these have been studied in the general population as well as in specific working environments. There is increasing evidence that the upper and lower airways should be considered as one unit and that rhinitis, if debut is before asthma, may be not a risk factor, but an early manifestation of the disease.3 ,4
A history of occupational exposure to the composite measure vapours, gases, dusts and fumes (VGDF) has been shown to almost double the risk of incident asthma,5 and to increase the risk of developing nasal congestion and rhinorrhoea.6 VGDF includes a large number of both specific and non-specific agents, and it is unclear to what extent the different components explain the observed association with respiratory symptoms and conditions. Studies of occupational exposure to different types of dust have found an association with persistent cough and wheezing, while studies of occupational exposure to chemicals have found an association with asthma.7 It has also been reported that exposure to either wood dust, metal or chemicals is associated with adult-onset rhinitis.8 However, VGDF and its components, such as inorganic dust, organic dust and chemicals, have rarely been evaluated simultaneously in relation to asthma, rhinitis and concomitant asthma and rhinitis in population-based samples.
The aim of this population-based study was to evaluate occupational exposure to the composite measure VGDF, and the importance of the components chemicals, inorganic dust and organic dust as risk factors for rhinitis, asthma and concomitant asthma and rhinitis.
Material and methods
Study population
The Obstructive Lung disease In Northern Sweden (OLIN) studies recruited three adult population-based cohorts during the 1980s and 1990s. The recruitment process was similar for all three cohorts (flow chart, see online supplementary figure 1); a postal questionnaire survey was carried out for age-stratified (cohorts 1 and 2) and random (cohort 3) samples of the population, which was followed up by clinical examination of samples of the responders. These samplings were made on the basis of reported respiratory symptoms (cohort 2 and part of cohort 1) and random selection (cohort 3 and part of cohort 1). The methodology has previously been described in detail.9–13 In 2002–2004, all previously clinically examined participants from these cohorts were invited for a re-examination, in which 4036 individuals participated. The study population in the current study includes data from the structured interview and a questionnaire regarding occupational exposure collected from the participants at the re-examination. The study was approved by the Regional Ethical Review Board of Umeå University.
Supplementary figures
Questionnaires
The structured interview included questions regarding respiratory symptoms and conditions, smoking habits, current and previous occupations. The questions included in the structured interview are well validated, and have been used in several national and international studies.9 ,12 ,14–16 The participants were also asked to complete a separate questionnaire regarding occupational exposure.
Definitions
BMI (body mass index): calculated as height/weight2 and classified according to the WHO standard;17 Smoking habits: never-smoker, ex-smoker (stopped more than 12 months ago) and current smoker. Ever-smoker was defined as ex-smoker or current smoker. Pack-years (PY): (number of smoked cigarettes per day x numbers of years smoked)/20. Socioeconomic status was based on reported current or last held occupation, and defined according to the socioeconomic classification by Statistics Sweden.18 Occupational exposure was self-reported. The questions stated were ‘During your working career, have you more often than occasionally been exposed to…?’; answers given were ‘yes’ or left without response and classified as follows: Inorganic dust: mineral, stone, quartz, coal (in spite of not being strictly inorganic), coke and metal dust. Organic dust: wood, paper, textile and flour dust. Chemicals: oil products, solvents, cleaning products, dyes, fully or partly uncured plastics, colours/varnishes, insecticides/pesticides, handling materials releasing chemicals at drilling, grinding, sawing, etc, aldehydes (formaldehyde, formalin), acrylates (thermoplastics or thermosets in colours, varnishes, glues, bone cement, dental filling materials), hair care products and isocyanates. VGDF was defined as an affirmative answer to any of the above stated occupational exposures and/or affirmative answer for questions regarding welding fumes and diesel exhaust. History of allergy: ‘Do you have allergic rhinitis and/or conjunctivitis?’ Asthmatic wheeze: affirmative answer to all of the following: ‘usually having wheezing or whistling in the chest during the past l2 months’, ‘any wheezing with shortness of breath’ and ‘any wheezing while not having a cold’. Rhinitis: ‘often being troubled by nasal congestion or rhinorrhoea’. Asthma: ‘Have you been diagnosed as having asthma by a physician?’ Concomitant asthma and rhinitis: both asthma and rhinitis, based on the definitions above. The terms rhinitis and asthma correspond to each condition irrespective of the other, while rhinitis only means those reporting rhinitis without concomitant asthma, and asthma only means asthma without concomitant rhinitis.
Statistics
Pearson χ2 was used for comparing prevalence between groups. Binary logistic regression was used to calculate crude ORs and 95% CIs risk for respiratory conditions in relation to occupational exposures. Multinomial logistic regression models were used to evaluate occupational exposures as risk factors for the mutually exclusive outcomes of rhinitis only, asthma only and concomitant asthma and rhinitis (reference category: neither asthma nor rhinitis). Exposure to VGDF and each of the components (chemicals, inorganic and organic dust) were analysed separately and in addition, an analysis was performed including all components at the same time. Chemicals were also analysed after excluding isocyanates, and further after excluding isocyanates and welding fumes. The multinomial analyses were adjusted for sex, age, BMI and smoking habits, and were also executed stratified by sex, by smoking habits and by allergy. The analyses were also separately adjusted for socioeconomic status and for allergy. The number of missing values was generally low for all variables, at most 0.1%. The level of statistical significance was p<0.05. All analyses were carried out using IBM SPSS statistics V.23.
Results
Basic characteristics and prevalence of respiratory symptoms
The mean age of the study population was 59.4 years (range 31–85 years), without sex difference. The burden of tobacco smoking was higher among men, assessed as both smoking habits and PY (22.5 among men and 14.0 among women, p<0.001). All respiratory symptoms and conditions were more common among women than men (table 1). The overlap between asthma and rhinitis is illustrated in online supplementary figure 2. Occupational exposure to VGDF and each of the components chemicals, inorganic and organic dust was significantly more common among men. Exposure to chemicals was the most common in the study population and also among women; among men, exposure to inorganic dust was the most common (table 1). The overlap between occupational exposure to chemicals and dust was considerable with 24.5% reporting simultaneous exposure (9.4% of women and 40.0% of men, p<0.001) (see online supplementary figure 3).
Occupational exposure as risk factors for asthma and rhinitis
Bivariate analyses of occupational exposures as risk factors (OR, 95% CI) for asthma and rhinitis are shown in table 2. VGDF yielded a borderline significant increased risk of asthma in the total population. Among women, exposure to VGDF increased the risk of asthma and concomitant asthma and rhinitis; for men, however, the risk of rhinitis and asthma was increased. In the total study population and for both sexes, exposure to chemicals, but not dusts, increased the risk of all conditions; rhinitis, asthma and concomitant asthma and rhinitis.
Multivariate analyses of risk factors for rhinitis only, asthma only and concomitant asthma and rhinitis
Exposure to VGDF increased the risk of asthma only and concomitant asthma and rhinitis in a model adjusting for sex, age, BMI and smoking habits. When the components chemicals, inorganic and organic dust were added, one at a time, to a similar model; exposure to chemicals (but not any of the dust-variables) increased the risks for rhinitis only, asthma only and concomitant asthma and rhinitis (table 3). Among women, exposure to VGDF increased the risk of concomitant asthma and rhinitis, and exposure to chemicals showed a similar pattern. Among men, exposure to VGDF increased the risk for rhinitis only and asthma only while exposure to chemicals increased the risk of all conditions; rhinitis only, asthma only and concomitant asthma and rhinitis. Among men, the exposure to inorganic dust increased the risks of asthma only (table 3). When all the components chemicals, inorganic and organic dust were included in the same model, exposure to chemicals remained significantly associated to an increased risk for rhinitis only, asthma only and concomitant asthma and rhinitis (figure 1), and the analyses stratified for sex showed a similar pattern (see online supplementary figure 4). Including the variables socioeconomic status and history of allergy into the model did not change the main results.
Sensitivity analyses
After excluding exposure to isocyanates and isocyanates and welding respectivley, exposure to chemicals remained an increased risk for rhinitis only, asthma only and concomitant asthma and rhinitis when analysed in a similar multivariate model adjusting for sex, age, BMI, smoking habits and inclusive of the dust-variables (table 4). Including socioeconomic status and history of allergy in the models did not change the results. Among women, the risk for asthma only and concomitant rhinitis and asthma was increased; among men, risks for rhinitis only and concomitant rhinitis and asthma increased.
Analyses were also performed stratified by smoking status. Among never-smokers, exposure to chemicals increased the risk for rhinitis only, asthma only and concomitant asthma and rhinitis, and the pattern was also fairly similar after excluding exposure to isocyanates respectively both isocyanates and welding fumes. Among ever-smokers, chemicals increased the risk for asthma only; the pattern was also the same when excluding isocyanates and welding fumes.
In analyses performed among participants without a history of allergy, chemicals remained a risk factor for rhinitis only and concomitant asthma and rhinitis but not for asthma only, when excluding isocyanates and welding fumes (table 4). Neither of the dust variables included in any of the above models yielded any significant results.
Discussion
In this population-based cross-sectional study, occupational exposure to VGDF was associated with an increased risk for asthma only and concomitant asthma and rhinitis, and exposure to chemicals, but not inorganic and organic dust, yielded a similar pattern. Men were, in general, more exposed than women, and there was a substantial overlap between exposure to chemicals and dusts. However, the observed increased risk for rhinitis only, asthma only and concomitant asthma and rhinitis associated with occupational exposure to chemicals persisted independent of concomitant exposure to inorganic or organic dust. Thus, occupational exposure to chemicals seems to be an important factor contributing to the association between exposure to the composite measure VGDF and rhinitis and asthma. The risk factor pattern was fairly similar among women and men, as well as among non-smokers and participants without a history of allergy.
Occupational exposure to unspecified airborne chemicals has rarely been evaluated in population-based studies. A recent publication including a selected population of participants with work-related asthma reported that exposure of miscellaneous chemicals was associated with asthma in 20% of women and 16% of men.19 Most studies use either reported exposure to gas, dust and fumes or the wider composite concept VGDF,20 ,21 or exposure to specific substances such as cleaning agents, pesticides, acrylates, aldehydes, dyes and solvents,22–24 or exposure evaluated in relation to job titles or a job exposure matrix.25 ,26 In a previous Swedish population-based study, occupational exposure to gas, dust and fumes was associated with an increased risk for asthma only as well as concomitant asthma and rhinitis,21 which is similar to our findings associated with exposure to VGDF. In the referred Swedish study, almost two-thirds of those with a diagnosis of asthma had allergic rhinitis and 40% chronic rhinitis;21 in our study also there was a substantial overlap between asthma and rhinitis. The overlap between upper and lower airway conditions, and the observed increased risk of concomitant asthma and rhinitis associated with exposure to VGDF are supportive of the united airway hypothesis.
In our study, exposure to chemicals, but not to inorganic and organic dust, yielded similar risk factor patterns as exposure to the composite measure VGDF. The risk for asthma after exposure to isocyanates and welding fumes is well known,27 and these substances may contribute to the observed increased risk for respiratory conditions among participants exposed to chemicals. However, the increased risk for respiratory conditions after exposure to chemicals was similar even after excluding exposure to isocyanates as well as exposure to both isocyanates and welding fumes, and a similar pattern was also seen among never-smokers and this is independent of exposure to dust. Thus information on general occupational exposure to unspecified chemicals is important for the medical evaluation of participants with asthma and/or rhinitis in the clinical setting. To the best of our knowledge, the present study is one of the first studies indicating that occupational exposure to chemicals may be an important factor driving the observed association between the composite measure VGDF and respiratory conditions, such as rhinitis and asthma, in the population. However, our study cannot distinguish to what extent the underlying mechanism of sensitisation to certain chemicals or airway inflammation is induced by chemical irritants, even though the most commonly known occupational allergen, isocyanates, has been excluded. Furthermore, cross-sectional studies, such as ours, can only describe associations and not evaluate cause and effect.
In population-based studies of occupational health, sex is most often evaluated as a risk factor, while possible sex-dependent differences in respiratory symptoms related to occupational exposure are seldom considered.28 ,29 Sex-stratified analyses are required to evaluate possible different risk factor patterns30 as it has been indicated that men and women react differently to dusty environments. In a review of studies on dusty working environment, female sex was associated with asthma and nasal symptoms, while male sex was associated with chronic cough and chronic phlegm.31 In our study, there was no relationship between dust exposure and asthma among women, while inorganic dust increased the risk of asthma among men. Furthermore, exposure to chemicals increased the risk for rhinitis only among men but not among women. There seems to be sex-differences regarding reported occupational exposures; for example, men were more likely to report exposure dust and chemical substances than women in the same occupations.32 We cannot establish whether these sex-differences are a result of biological differences, or due to exposure to different substances or chemicals. Even though occupational exposure, in general, was more common among men, both sexes had a fairly similar pattern regarding risk of asthma, rhinitis and concomitant asthma and rhinitis after exposure to the composite measure VGDF as well as chemicals in our study.
In occupational studies, the healthy worker effect must be considered.33–35 First, the selection into job bias: workers not in good health tend to avoid risky jobs, and they can also be rejected at pre-employment screening, resulting in workers in better health than the general population. Second, the selection out-of-job bias: workers with deteriorating health will tend to leave their work place which will also result in a workforce with better health than the general population. It is difficult to control for the healthy worker effect in a cross-sectional study. Both types of healthy worker effect biases may result in our observed associations being an underestimate of the true associations. On the other hand, occupational exposure was based on self-reporting, and recall bias cannot be excluded; those with respiratory symptoms/conditions may have been more prone to report previous occupational exposure. Another limitation is that asthma is self-reported and not verified by medical records or, for example, methacholine provocation.
Occupational exposure can be estimated not only by using a single-item question of exposure but also by using multiple-item questions, as in our study, or by using a job exposure matrix (JEM) based on job titles.36 Some argue that a JEM leads to more accurate measures of occupational exposure, while others have shown that the difference between self-reporting and JEM are smaller than expected and that the question of VGDF-exposure is applicable in epidemiological research.36–38 However, it should be noted that self-reporting usually yields higher risks and more strongly statistically significant results than a JEM.36 The sizes of the risk estimates in this study may not be fully generalisable to the general population as the study population was enriched with participants with respiratory symptoms.
In conclusion, according to this population-based study, occupational exposure to chemicals may be an important component contributing to the increased risk of asthma and rhinitis observed for occupational exposure to VGDF. Occupational exposure to chemicals seems to affect both upper and lower airways in both sexes, in line with the united airways hypothesis. The results suggest that an increased vigilance regarding occupational exposure to chemicals may have a beneficial effect on respiratory health of the population.
Acknowledgments
Statisticians Helena Backman and Ola Bernhoff are acknowledged for their support with statistical questions and for comprising the data file. The authors also thank research assistants Ann-Christin Jonsson and Sigrid Sundberg for collecting the data.
References
Footnotes
Contributors CS carried out the statistical analyses and drafted the manuscript. ER, BL and AL contributed in the study design, collection of data and critical revision of the manuscript. AL also contributed in drafting the manuscript. MA and UH critically revised the manuscript, especially with regard to occupational exposures. LH contributed with critical revision of the manuscript, statistical advice and collection of data.
Funding Financial support from the Swedish Heart and Lung Foundation, Swedish Asthma and Allergy Association, Visare Norr (a research foundation sponsored by Northern Sweden healthcare authorities and Umeå University), Norrbotten County Council and Blekinge County Council is gratefully acknowledged.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Ethical Review Board of Umeå University, Umeå, Sweden.
Provenance and peer review Not commissioned; externally peer reviewed.