‘Jobs identified that are linked to greater risk of asthma in adults’, reports The Daily Telegraph, while BBC News tells us that ‘cleaning products’ are to blame.
The news is based on a large UK study that looked at the major occupations and occupational exposures associated with the development of asthma in British adults. Researchers found that 18 occupations, including care workers and hairdressing, were associated with an increased risk of adults reporting asthma. Interestingly, only four occupations of the 18 were found to be significantly associated with an increased risk when asthma was diagnosed with lung function testing rather than self-reporting. These occupations were:
- office and hotel cleaners
- doorkeepers (which is not defined but may refer to security guards or bouncers)
- manufacturing labourers
- ‘hand packers’
The researchers make the case that exposure to certain chemicals, such as cleaning products, could explain this increased risk, though the association with doorkeepers is puzzling.
It is worth noting that this study does not provide evidence of a cause and effect (causal) relationship, only an association. There may be other factors at play (confounders), that the researchers did not account for, such as a family history of asthma.
If you are concerned that your workplace is contributing towards your symptoms of asthma, you should speak to your employer. There may be simple changes they can make in your workplace to improve the situation.
Where did the story come from?
The study was published in the peer-reviewed respiratory medical journal, Thorax.
The BBC and the Telegraph covered the story appropriately; however, the headlines suggest a causal relationship, which is not the case.
What kind of research was this?
This was a re-analysis of data collected from an ongoing cohort study which started in 1958. It looked at the association between adult asthma and various high- or low-risk occupations where employees are known to be exposed to agents or triggers for the development of asthma. The researchers were interested in what proportion of adult asthma is due to exposure in these occupations.
Cohort studies are useful for looking at possible associations between various lifestyle factors (such as occupation or occupational exposures) and health outcomes (such as an adult’s development of asthma). They enable researchers to follow large groups of people for many years, but they cannot establish cause and effect, only highlight possible associations.
What did the research involve?
The researchers analysed 11,000 people born in 1958 and living in the UK who were part of the larger National Child Development Study. These people were tracked over their lifetime, and for the purposes of this study, researchers used data up to age 45 years. Information was collected on self-reported asthma or wheezy bronchitis through interviews carried out at ages 7, 11, 16, 33 and 42 (parents were questioned for the interviews at ages 7, 11 and 16).
Participants were also interviewed at age 33 and 42, where they were asked about their jobs. They were asked to give a short description of their jobs from the ages of 16 to 42. A job was defined as lasting more than one month and included part-time or temporary work. Finally, participants had lung function testing at ages 44 and 45.
Individual occupational exposures were determined from the Asthma Specific Job Exposure Matrix, which assigns work-place exposures to 18 high-risk substances, such as flour, cleaning products and metal fumes. According to the researchers, jobs not assigned to these ‘high-risk’ substances were defined by the matrix as ‘low-risk’ or ‘non-exposed’. Office-based work was considered non-exposed.
Adult onset asthma was considered present when a participant reported they ‘ever had asthma’ at ages 33 or 42. Adult asthma with airflow limitation was considered present when confirmed on lung functioning testing. Lifetime exposure was considered as either:
- low-risk only
- high-risk only
- high-risk and low-risk
The researchers adjusted their results for smoking, gender, father’s social class, area of residence at age 42 and childhood hay fever. Participants who reported ever having had wheezy bronchitis or asthma at any of the surveys in childhood (ages 7, 11 and 16) were excluded.
What were the basic results?
A total of 7,406 participants were analysed after excluding 2,082 people who reported asthma or wheezy bronchitis during childhood. Of the 7,406 participants, 639 people (9%) had reported asthma by age 42. The main results were:
After testing, 18 of the total of 61 occupations were associated with self-reported adult onset asthma, with an increased odds ratio ranging from 1.50 for waiting staff to 4.26 for farmers. Other occupations included:
- aircraft mechanics
- building construction workers
- care workers
Four of the 18 occupations associated with reported adult onset asthma were also significantly associated with asthma airflow limitation (confirmed on lung function testing), however numbers were small and not all 18 occupations were able to be tested. These four occupations were:
- office and hotel cleaners
- manufacturing labourers
- hand packers
By age 42, 25% of participants were considered non-exposed, 8% had been exposed to high-risk agents, 28% to low-risk agents and 34% had been exposed to low-risk and high-risk agents. Having been exposed to high-risk agents was associated with a higher risk of reported adult onset asthma, irrespective of exposure to low-risk agents. Exposure to low-risk agents was not associated with an increased risk of reported adult onset asthma.
How did the researchers interpret the results?
The researchers conclude that approximately 16% (around one in six) of adult onset asthma in British adults born in the late 1950s could be due to occupational exposures, mainly recognised as high-risk exposures.
Lead researcher Dr Rebecca Ghosh, is reported as saying ‘occupational asthma is widely under-recognised by employers, employees and healthcare professionals. Raising awareness that this is an almost entirely preventable disease would be a major step in reducing its incidence’.
The results of this large study offer evidence of an association between occupational exposures and onset of asthma as a child. Importantly, it quantifies the proportion of asthma that is likely to be due to exposure to occupational agents.
There are several imitations to this study:
- Despite the authors’ efforts to adjust their results for confounders, it is always possible that other factors such as a family history of asthma influenced the results.
- Asthma confirmed with lung function testing was less prevalent than self-reported asthma or wheezy bronchitis. This suggests that some of the self-reported asthma, may have in fact not been confirmed as asthma on clinical diagnoses had they undergone lung function testing when they were reported – therefore allowing asthmas to be overestimated.
- The researchers were unable to rule out the possibility that participants who reported asthma or were diagnosed with lung function testing, had other respiratory conditions such as chronic obstructive pulmonary disease (COPD).
- Although the researchers attempted to estimate individual level exposures, these are still estimations made from the type of jobs they do and may not reflect actual exposure.
- It is likely that different people working in the same type of job had different exposures. It is also unknown if steps were taken by individuals to lessen exposure to agents (for example, if protective equipment such as face masks were worn while working).
- The authors note that unemployed and ethnic minority groups are under-represented in the participants included in the study.
Overall, this study is well-designed to answer a well-defined research question. It provides a good reason for extra care to be taken by employers and those working in jobs with high-risk exposures, especially those likely to involve exposure to cleaning agents.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 22 January 2013
The Daily Telegraph, 22 January 2013
Links to the science
Thorax. Published online January 21 2013