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Exposure to pollution linked to uncontrolled asthma

Long-term exposure to air pollution is strongly linked to uncontrolled asthma, suggests research published online in the Journal of Epidemiology and Community Health.

The findings held true irrespective of risk factors traditionally associated with worsening or poorly controlled asthma, such as smoking, weight and use of inhaled corticosteroids.

It is known that air pollution has a role in worsening respiratory symptoms, including increased use of medication and admissions to hospital, but it has not been clear what, if any, effect long term air pollution has on the control of asthma.

The researchers base their findings on 501 adults with active asthma who completed a detailed questionnaire on respiratory health between 2003 and 2007.

Asthma control was measured according to symptoms, asthma attacks, and lung function or FEV1.

Just under half (44%) of the 481 asthmatics for whom information on pollutant levels was available had well controlled asthma. In 29% the asthma was partially controlled; but in more than one in four (27%) symptoms were uncontrolled.

Levels of ozone and particulate matter were strongly associated with poorer asthma control, with long term exposure to ozone conferring a 69% increased risk of uncontrolled asthma and particulate matter increasing the risk by 35%.

Both pollutants were associated with each of the three measures used to assess asthma control. Women and older people were more likely to have poorly controlled asthma.

"Our results indicate that both ambient O3 and PM10 concentrations jeopardise asthma control in adults," conclude the authors, adding: "The results are robust."

Journal of Epidemiology and Community Health