August 8, 2019

expert reaction to study looking at air pollution and childhood asthma in Europe

Research, published in the European Respiratory Journal, reports that 33% of new childhood asthma cases in Europe are attributable to air pollution.

Prof Anna Hansell, Professor in Environmental Epidemiology, University of Leicester, said:

Does the press release accurately reflect the science?

“Yes.

Is this good quality research?  Are the conclusions backed up by solid data?

“This is a well-conducted study, using standard methods for estimating burden of disease.  It combines evidence from 41 scientific papers investigating relationships between air pollution and asthma and uses a robust method to estimate population air pollution exposures across Europe.  It then combines this with country specific asthma rates (which vary) and predicts the percentage of cases attributable to air pollution.

“The results make for sobering reading!

How does this work fit with the existing evidence?

“The study findings are consistent with previous studies for specific European areas.

Have the authors accounted for confounders?  Are there important limitations to be aware of?

“A very important limitation pointed out by the authors is that the figures are not adjusted for other pollutants (e.g. PM2.5 is not adjusted for NO2 exposure that will be occurring at the same time).  So where they state “lowest levels of NO₂ and black carbon were achieved would be 135,000 (or 23%) and 89,000 (or 15% of all incident cases), respectively”, it is *not* correct to add up the numbers (135000+89000) or (23% + 15%) as that would over-estimate the numbers or % of cases attributable to air pollution.

“Asthma is a complex disease and diagnosis rates vary between European countries, which may be due to differences in the way in which the diagnosis is made rather than in rates of underlying disease.  This may affect the number of cases attributed to air pollution.

“The air pollution exposure estimates are average area exposures for populations within 1km area squares.  Personal exposures may vary e.g. if living near a main road or a park.  The exposures relate to outdoor levels – while a good proportion of outdoor air pollution penetrates indoors, the amount that does so varies depending on type of house, ventilation etc.  Also people spend varying times indoors.

“The methods do not take account of factors such as deprivation (which make worsen the impact of air pollution) or diet and exercise that potentially have beneficial effects that offset the impacts of air pollution.

What are the implications in the real world?  Is there any overspeculation?

“It has been clear for many years that we need to reduce air pollution exposure.  Most studies previously have concentrated on air pollution contributions to mortality.  Studies like this show how very important it is to also consider children’s health.

“The lowest levels of air pollutants recorded by previous studies are extremely low – they represent for example, what you might record in unpolluted areas in northern Scandinavia.  We would need a complete overhaul of our traffic and emissions policies to achieve this.

“As well looking at air pollution regulations, we need to look at interventions to reduce individual’s exposures to air pollution.  We also need more scientific studies on factors, for example in the diet, that may reduce harmful effects of air pollution.”

Prof Stephen Holgate, RCP Special Advisor on Air Quality and UKRI Clean Air Champion, University of Southampton, said:

“This ground-breaking study confirms the massive impact that air pollution has on childhood asthma, not only in making it worse in those who already suffer, but initiating new asthma in those who otherwise would not have the disease.  The U.K. has among the highest prevalence of asthma worldwide and, in Europe, among the greatest deaths from this devastating disease.  The study emphasises the enormous impact that adhering to WHO air pollution limits for PM2.5 and NO2 would create a massive health gain for this vulnerable population.  Brexit presents the UK with a unique opportunity to set such standards for the health of the future generation.”

‘Outdoor Air Pollution and the Burden of Childhood Asthma across Europe’ by Haneen Khreis et al. was published in the European Respiratory Journal at 00:01 UK time on Thursday 8 August 2019. 

DOI: 10.1183/13993003.02194-2018

Declared interests

Prof Anna Hansell: “None.”

None others received.