March 24, 2015

expert reaction to two papers on air pollution and stroke/anxiety

Two papers have been published in The BMJ regarding the effects of air pollution on cases of stroke and symptoms of anxiety, with the research groups reporting an association between higher levels of air pollution and both illnesses.

Prof. Jon Ayres, Professor of Environmental & Respiratory Medicine at the University of Birmingham, said:

“It has long been thought that exposure to air pollution is associated with stroke and this meta analysis confirms the association with a range of pollutants. Mechanistically the most likely agent are particles and from these data those smaller than 2.5 microns seem the most likely causal agents. Gases at such low concentrations are very unlikely to have an effect on vascular endothelium. In particular, the high solubility of SO2 will not allow the gas to penetrate beyond the respiratory mucosa and so will not influence the vascular tree. That effects are more marked in low/middle income countries may be a reflection of a higher mean concentration in those countries. It would have been helpful to see the data analysed in this way to explore this further.

“The study purporting to link air quality to anxiety is much less convincing. By far the most likely explanation, especially given that more recent exposure has a greater effect, is that the anxiety relates to traffic (noise, increased risk of accident) than to air pollutants themselves. Even though the authors say that living nearer to main roads was allowed for, this does not take away concern that having to walk/drive around in an area with greater traffic flows was not the major influence on this association. Other potential confounders such as green space were also not allowed for. There are also no real plausible mechanisms why this association shouldn’t be other than one which has arisen by chance. I am surprised that this was accepted for publication given these weaknesses and concerned that this will result in inappropriate anxiety in readers.”

‘Short term exposure to air pollution and stroke: a systematic review and meta analysis’ by Anoop Shah et al and ‘The relation between exposure to fine particulate air pollution and anxiety: a cohort study’ by Melinda Power et al published in the BMJ on Tuesday 24 March 2015. 

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/tag/air-pollution/

Declared interests

Prof. Ayres is former chair of DH’s Committee on Medical Effects of Air Pollutants (COMEAP) and served on DEFRA’s Expert Panel on Air Quality Standards (EPAQS)