Workplace air pollution increases risk of asthma in men

A new study reveals that exposure to non-sensitising air pollution at work significantly increases a man's risk of developing adult-onset asthma but has no corresponding effect in women.

It is now well established that acute workplace exposure to high levels of sensitising chemicals, including chlorine, ammonia, ozone and sulphur dioxide, can trigger so called reactive airway dysfunction syndrome (RADS) and cause late-onset asthma in adults. There has been much less research looking at chronic low level exposure to air pollution considered non-sensitising, such as dust, smoke and fumes from non-sensitising chemicals. The suggestion that such low-level chronic exposures can cause asthma has generated a not unsubstantial amount of debate, much like the issue of chronic low-level chemical exposures leading to multiple chemical sensitivity (MCS).

A Swedish research team sought to clarify the role of chronic low-level exposure to non-sensitising air pollutants in adult-onset asthma  and address the controversy surrounding the issue. The scientists, based at the Clinic of Occupational and Environmental Medicine, University Hospital, Linkoping, designed a case-control study involving 192 adult-onset asthma cases and 323 healthy control subjects, all aged between 20 and 65.

The cases were identified from computerised registers covering the southeastern region of Sweden and then confirmed via medical records. To be included in the study's analysis the cases must have been diagnosed with asthma during the period from the year 2000 to 2004. Potential participants were randomised to obtain a study sample with a mix of attributes such as sex, age, ethnicity and field of work to ensure it represented a close approximation of the population of the region and the results could therefore be taken to apply to the population as a whole.

Participants were asked to complete a 16 page questionnaire that sought to ascertain their occupational exposure to non-sensitising air pollution over previous years. Since the goal of the research was to determine if this non-sensitising type of pollution specifically could cause adult-onset asthma, the scientists devoted special attention devoted to identifying exposures to known sensitising substances (e.g. chlorine, ozone etc) and to exclude participants exposed to these substances from the final analyses.

After looking at the data obtained through the questionnaires and medical records the researchers found that three years or more of workplace exposure to air pollution from dust, smoke, or fumes more than doubled the risk for asthma in men, but no such increase in risk was seen in women. Further analysis using multiple logistic regression for men without a history of childhood allergy found they were almost 3 times as likely to develop asthma after chronic workplace air pollution exposure than those not exposed, when subjects exposed to identified allergens were excluded.

The researchers concluded that their findings supported a role for chronic exposure to low level, non-sensitising air pollution in the workplace and the development of adult-onset asthma in men.

Further research on a larger scale will be required to confirm these results and also to explain why it is that occupational exposure to air pollution of this type does not appear to affect women's risk for adult-onset asthma.

Source: Graff P Fredrikson M Jönsson P Flodin U (2011) Non-sensitising air pollution at workplaces and adult-onset asthma in the beginning of this millennium International Archives of Occupational and Environmental Health [Epub ahead of print] PMID:21720882