Exposure to outdoor air pollution is linked to decreased lung function and an increased risk of developing chronic obstructive pulmonary disease (COPD), according to a study of over 300,000 people published Tuesday.
COPD is a long-term condition linked to reduced lung function that causes inflammation in the lungs and a narrowing of the airways, making breathing difficult.
According to the Global Burden of Disease (GBD) project COPD is the third leading cause of death worldwide, and the number of global COPD deaths are expected to increase over the next ten years.
Lung function normally declines as we age, but the research published in the European Respiratory Journal suggests that air pollution may contribute to the ageing process and adds to the evidence that breathing in polluted air harms the lungs.
"There are surprisingly few studies that look at how air pollution affects lung health," said Anna Hansell, a professor at the University of Leicester, UK.
The researchers used a validated air pollution model to estimate the levels of pollution that people were exposed to at their homes when they enrolled in the UK Biobank study.
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The types of pollutants the researchers investigated included particulate matter (PM10), fine particulate matter (PM2.5) and nitrogen dioxide (NO2), which are produced by burning fossil fuels from car and other vehicle exhausts, power plants and industrial emissions.
The team then conducted multiple tests to see how long-term exposure to higher levels of the different air pollutants was linked to changes to participants' lung function.
The participants' age, sex, body mass index (BMI), household income, education level, smoking status, and exposure to secondhand smoke were accounted for in the analyses.
Further analyses also looked at whether working in occupations that increase the risk of developing COPD impacted disease prevalence.
The data showed that for each annual average increase of five microgrammes per cubic metre of PM2.5 in the air that participants were exposed to at home, the associated reduction in lung function was similar to the effects of two years of ageing.
When the researchers assessed COPD prevalence, they found that among participants living in areas with PM2.5 concentrations above World Health Organization (WHO) annual average guidelines of ten microgrammes per cubic meter, COPD prevalence was four times higher than among people who were exposed to passive smoking at home, and prevalence was half that of people who have ever been a smoker.
The current EU air quality limits for PM2.5 is 25 microgrammes per cubic metre, which is higher than the levels that the researchers noted as being linked to reduced lung function.
"In one of the largest analyses to date, we found that outdoor air pollution exposure is directly linked to lower lung function and increased COPD prevalence.
"We found that people exposed to higher levels of pollutants had lower lung function equivalent to at least a year of ageing," Hansell said.
"Worryingly, we found that air pollution had much larger effects on people from lower income households. Air pollution had approximately twice the impact on lung function decline and three times the increased COPD risk on lower-income participants compared to higher-income participants who had the same air pollution exposure.
"We accounted for participants' smoking status and if their occupation might affect lung health, and think this disparity could be related to poorer housing conditions or diet, worse access to healthcare or long-term effects of poverty affecting lung growth in childhood," Hansell said.