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Air pollution reduces lung function, increases risk for COPD

Air pollution appears to be associated with reduced lung function and an increased risk for COPD, especially among people with lower incomes, new study results published in the European Respiratory Journal suggest.

“There are surprisingly few studies that look at how air pollution affects lung health,” Anna L. Hansell, MD, PhD, professor of environmental epidemiology in the Centre for Environmental Health and Sustainability at the University of Leicester in the United Kingdom, said in a press release. “To try and address this, we assessed more than 300,000 people using data from the UK Biobank study to examine whether air pollution exposure was linked to changes in lung function, and whether it affected participants’ risk of developing COPD.”

Hansell and colleagues estimated the levels of pollution to which study participants were exposed using a validated air pollution model. In particular, they assessed exposure to particulate matter 10 µm or less in diameter (PM₁₀), fine particulate matter (PM_2.5) and nitrogen dioxide. As part of the UK Biobank data collection, participants completed health questionnaires and spirometry was used to measure lung function.

The researchers accounted for various participant characteristics, including age, sex, BMI, household income, education level, smoking status and exposure to secondhand smoke, in their analyses. They also examined the association between occupations that place people at an increased risk for COPD and prevalence of the disease.

Effects of air pollution

The data demonstrated a significant association between higher exposure to pollutants and reduced lung function. Specifically, each 5-g/m³ increase in PM_2.5 exposure resulted in lower FEV₁, FVC and FEV₁:FVC that was on par with the effects of 2 years of aging. Similar results were noted with each 10-g/m³ increase in nitrogen dioxide.

FEV₁ and FVC were also lower with exposure to PM₁₀ and coarse particulate matter between 2.5 m and 10 m in diameter. However, exposure to particulate matter was not associated with FEV₁:FVC and there was a slight positive association between exposure to coarse particulate matter and FEV₁:FVC.

In analyses of COPD, prevalence increased with each 5-g/m³ increase in exposure to PM_2.5 (OR = 1.52; 95% CI, 1.42-1.62), each 10-g/m³ increase in exposure to PM₁₀ (OR = 1.08; 95% CI, 1-1.6) and each 10-g/m³ increase in exposure to nitrogen dioxide (OR = 1.12; 95% CI, 1.1-1.14). However, COPD prevalence was not associated with exposure to coarse particulate matter.

Furthermore, the prevalence of COPD attributable to living in areas where PM_2.5 exceed WHO guidelines (5.6%) was nearly half that of prevalence attributable to current or past tobacco smoking (12.1%) and more than fourfold higher than the prevalence attributable to exposure to passive smoking at home (1.2%).

In subgroup analyses, the associations between exposure to PM_2.5 and nitrogen dioxide and lower FEV₁ were stronger among men, people with lower incomes and those with occupations determined to be at risk for COPD. FVC was also lower in relation to exposure in these subgroups, as well as in people who never smoked. Notably, FEV₁ and FVC levels were about twice as low among people from lower-income households than among both those from higher-income households and those with at-risk occupations.

Additionally, the adverse association between lower FEV₁:FVC and exposure to PM_2.5 and nitrogen dioxide exposure was stronger among people who were older, obese and current or past smokers, and those with lower income. Similarly, the associations between COPD prevalence and exposure to PM_2.5 and nitrogen dioxide were stronger among obese and lower-income patients and those without asthma. Household income was, again, an effect modifier: Associations between COPD and each pollutant were three times as strong among lower-income participants vs. higher-income participants.

Ramifications

These findings suggest that air pollution may have significant adverse effects on respiratory health, according to Hansell.

“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 aging,” she said in the release.

“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.”

Hansell noted that the circumstances in which people with lower household income live may be a factor.

“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 health care or long-term effects of poverty affecting lung growth in childhood. However, further research is needed to investigate the differences in effects between people from lower- and higher-income homes,” she said.

Overall, though, the study population was generally wealthier and healthier than the general public, meaning that the association between air pollution and lung function may be underestimated, the researchers noted.

“The findings of this large study reinforce that exposure to polluted air seriously harms human health by reducing life expectancy and making people more prone to developing chronic lung disease,” Tobias Welte, MD, professor of respiratory medicine at Hannover University in Germany and president of the European Respiratory Society, said in the release.

The study results also emphasize a larger message, Welte added.

“Access to clean air is a fundamental need and right for all citizens in Europe. Governments have a responsibility to protect this right by ensuring that maximum pollutant levels indicated by the World Health Organization are not breached across our cities and towns. Breathing is the most basic human function required to sustain life, which is why we must continue to fight for the right to breathe clean air,” he said. – by Melissa Foster

Disclosures: The authors report no relevant financial disclosures.