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expert reaction to air pollution and childhood asthma

Research published in The Lancet Planetary Health suggests that pollution guidelines may need to be re-evaluated as a reduction in NO2 exposure could help prevent a substantial portion of new paediatric asthma cases.

Prof. Jonathan Grigg, Professor of Paediatric Respiratory and Environmental Medicine, Queen Mary University of London, said:

“Asthma is a major non-communicable disease with adverse effects across the life course. In the past, asthma was considered to be a disease of high-income countries, but now most affected people live in low- and middle-income countries, where asthma prevalence is increasing fastest ( The study by Achakulwisut et al, is therefore important since it seeks, for the first time, to qualify the effect of modelled exposure to nitrogen dioxide (NO2) on the global burden of asthma in children.

“The study’s estimate of 4 million new cases of asthma per year in children due to air pollution is compatible with other studies reporting an association between air pollution and new onset asthma. For example, a European study published in Lancet Respiratory Medicine in 2015 by Gehring et al reported an increased risk of new-onset asthma in children exposed to higher concentrations of NO2. It is important to note that NO2 in the global study by Achakulwisut et al is used as a marker of the complex mix of emissions from traffic. Thus, air pollution exposure-reduction policies aimed at reducing new cases of paediatric asthma must target not only NO2, but also other components of the pollution mix including particulate matter (PM). Since the effects of air pollution on new-onset asthma in adults was not considered in the study, the global burden of asthma across the whole life course due to air pollution is likely to be substantially higher. Overall, the study of Achakulwisut et al provides further evidence that ultra-low-emissions zones, such as the one launched recently in London, must be of sufficient size to reduce exposure of all children living in these urban areas.”

Prof. Stephen Holgate, Professor of Immunopharmacology, University of Southampton, said:

“It has long been known that outdoor air pollution can trigger worsening asthma, but only recently has it been linked to the causation of new asthma. This remarkable study has used multiple measures of air pollution to evaluate its impact on a worldwide scale on new asthma with a particular emphasis on NO2, a major primary pollutant from traffic especially diesel vehicles. By connecting health data with pollution modelling the authors make a powerful case that, at levels below the WHO guidelines, NO2 exposure is linked to new asthma. This startling discovery mandates that NO2 as a toxic pollutant is taken more seriously and more stringent limits introduced to protect the generations to come.”

Dr Stefan Reis, Science Area Head, Atmospheric Chemistry & Effects, Centre for Ecology & Hydrology, said:

“The results of this comprehensive, global study serve as a timely reminder, that air quality guideline values are not designed to represent a ‘no effect’ threshold, below which air pollution exposure does not cause adverse health effects. WHO explicitly states this for fine particulate matter: “In addition to guideline values, the Air Quality Guidelines provide interim targets for concentrations of PM10 and PM2.5 aimed at promoting a gradual shift from high to lower concentrations”, and the same principles apply for other air pollutants. The currently ongoing review of the WHO guideline values will substantially benefit from such results. These findings are timely as well for the review and discussion of air quality objectives in the UK. They highlight the need to aim for substantive reductions in overall population exposure, rather than focusing on attainment of limit values at few monitoring sites. “

Dr Matthew Loxham, Fellow in Respiratory Biology and Air Pollution Toxicology in Medicine, University of Southampton, said:

“A similar study published in 2017 looking at the effects of air pollution in over 60 million people in the USA saw something similar, but with different pollutants – that exposure to PM2.5 and ozone below concentrations very similar to WHO guidelines was associated with a risk of death which, per amount of pollutant, was no less than the effects above the WHO guidelines. That air pollution causes adverse health effects below these guidelines, which are often significantly lower than legal limits, is beyond doubt. The issue is how we generate the data to decide what the guideline levels should be or, perhaps more fundamentally, get across the message that there is no appropriate guideline level.”

‘Global, national, and urban burdens of paediatric asthma incidence attributable to ambient NO₂ pollution: estimates from global datasets’ by Achakulwisut et al. was published in The Lancet Planetary Health at 23:30 UK time on Wednesday 10th April 2019.

Declared interests

Dr Stefan Reis: “No conflict of interest/competing interests to declare.”

None others received

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