Social Determinants in Asthma : Population-based studies on asthma and respiratory symptoms in relation to occupation, occupational exposure and socioeconomic status

Abstract: Background: Asthma is one of the most common chronic obstructive airway diseases among children and adults, with a prevalence between 6-11% in European countries. It is also the most common work-related occupational respiratory disease. There are different methods to classify occupational exposure and, even though there is no clear consensus on which method is the most accurate, the single-item question on exposure to the composite measure vapour, gas, dust or fumes (VGDF) is commonly used in epidemiological research. Low socioeconomic status is associated with asthma and also behavioural factors such as smoking and over-weight, which by themselves are risk factors for asthma. Socioeconomic status is, however, truly a multifaceted concept and using only one measure does not encompass its entire effect on health-related outcomes. Asthma does also have a negative impact on the quality of life among adolescents: they report less physical fitness compared to their peers and more school absenteeism due to respiratory symptoms. Still, research on whether childhood asthma has any impact on socioeconomic status in young adulthood is scarce.Aim: The overall aim is to study social determinants of health such as socioeconomic status, occupation and occupational exposure and their relationship with asthma and respiratory symptoms among adults and further, to evaluate if asthma during childhood or adolescence is associated with social determinants in young adulthood.Method: This thesis includes four papers based on data from the Obstructive Lung Disease in Northern Sweden (OLIN) studies. Papers I-III are cross-sectional studies among adults; a structured interview from clinical examinations between 2002-04 (paper I, n=4036) and postal questionnaire surveys from 2006 (paper II, n=9992) and 2016 (paper III, n=6854) with the addition of register-based data in paper III. Paper IV is a longitudinal prospective cohort study; the first OLIN paediatric cohort followed from 7 to 19 years of age and a postal questionnaire follow-up at ages 27-28 in 2015 (n=2017). Asthma was defined as physician diagnosis (paper I) together with respiratory symptoms (paper II-IV) or use of asthma medication (paper IV). In paper IV asthma was further categorized based on age of onset and p v and adolescence. Main or longest held occupation was used to categorize occupational and socioeconomic groups. In papers III and IV additional measures of socioeconomic status were included; educational level (papers III and IV) and income (paper III). In all papers, occupational exposure to vapour and/or gas, dust and fumes (VGDF or GDF) were taken into consideration and in paper I further divided into subgroups based on a detailed questionnaire on occupational exposure.Results: In paper I we found that the association between occupational exposure to VGDF and asthma and rhinitis was driven by the component of chemicals rather than dusts. In paper II, the ISCO-based manual Swedish Standard Classification of Occupations (SSYK) and the manual Socioeconomic classification (SEI), could both identify occupational and socioeconomic groups at risk for respiratory symptoms and asthma, while the older ISCO-based manual Nordic Classification of Occupations (NYK) was not as sensitive.In paper III, behavioural risk factors for respiratory symptoms and asthma such as smoking and obesity and, occupational exposure to GDF were associated with low educational level. Interaction analyses between income level and sex revealed different patterns among women and men. Among women, low income was associated with all respiratory symptoms as well as asthma, while among men only with productive cough.In paper IV, early onset asthma was associated with lower educational level in young adulthood, especially not continuing after compulsory school. Further, those with asthma during childhood or adolescence did not seem to refrain from smoking at age 19, nor did they as young adults seem to avoid occupations with known or expected exposure to GDF.Conclusions: Increased automation in industries have decreased the number of manual workers in industries with typically dirty tasks, meaning that the interrelationships between the subgroups included in VGDF may have changed. This may also affect the meaning of occupational exposure to VGDF, at least with regard to asthma and rhinitis, and according to our findings exposure to the component of chemicals may be the most important. We also found that the use of an ISCO-based manual (SSYK) as well as socioeconomic classification based on job-title (SEI) can be useful and easily applicable tools to identify occupational and socioeconomic groups at risk for respiratory symptoms and asthma. Further, low socioeconomic status is associated with respiratory vi symptoms and asthma. It seems as these associations relies more on low income than low educational level. Low educational level as well as low income are furthermore related to known behavioural risk factors for respiratory symptoms and asthma such as obesity, smoking and, also potentially modifiable risk factors as occupational exposure to gas dust or fumes. Having a persisting asthma since childhood is associated with lower educational level as a young adult. This may, in turn, be related with behavioural risk factors as discussed above and, there were no indications that those with child or adolescent asthma refrained from smoking at age 19. Neither did they in young adulthood avoid occupations with known or expected exposure to gas, dust or fumes, such as manufacturing, construction and transportation work. To conclude, our results indicate a vicious circle with regard to the relationship between the studied social determinants of health and asthma and respiratory symptoms.