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expert reaction to low levels of air pollution linked to changes in the heart

Researchers examine the association between ambient air pollution and cardiac morpho-functional phenotypes in a new study in Circulation.

 

Dr Holly Shiels, Reader in Physiology, Division of Cardiovascular Sciences, University of Manchester and Charlotte Marris, BHF PhD student working on air pollution in mammalian hearts, University of Manchester

  1. Does the press release accurately reflect the science?

“It does in part.  However, some of links the press release makes between the heart remodelling seen in the study and early stage HF are not reflected in the paper.

“Also the grounds for the statement ‘For every 1 extra µg per cubic metre of PM2.5 and for every 10 extra µg per cubic metre of NO2, the heart enlarges by approximately 1%’ is unclear.” – Charlotte Marris

  1. Is this good quality research?  Are the conclusions backed up by solid data? And how strong are the findings?

“Yes. The association between heart size and air pollution are intriguing and worrisome.  Other markers for cardiovascular disease could help confirm the seriousness of these finding for human health.” – Holly Shiels

  1. How clear is the link between air pollution and heart disease and other illnesses?

“This is an intriguing study showing clear associations between air pollution and cardiac size.  It does not yet explain the causality and this is where future work will need to focus.” – Charlotte Marris

  1. How does this work fit with the existing evidence?

“Oil spills, which release similar pollutants into the environment, are known to have serious negative effects on fish hearts, including changes in size and shape.  Thus, the cardiac association described here for humans, is in keeping with these earlier studies. It also increases the relevance of the work done on fish and crude oil pollution to human cardiovascular health.” – Holly Shiels

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

“Yes the authors have accounted for important confounders.  The authors have clearly stated the limitations within the paper.” – Charlotte Marris

  1. What are the implications in the real world?  Is there any over-speculation?

“This study suggests current air pollution levels are already high enough to alter heart structure; therefore current air quality standards are not stringent enough.  Therefore this study provides important information for policy makers, especially those in urban areas.” – Holly Shiels

  1. Should people be worried about air pollution exposure?

“This study consolidates on the already concerning phenomenon that air pollutants produce detrimental effects on the heart. The British Heart Foundation is already funding studies to try and understand the mechanism behind these effects in order to target key issues. However, research such as this requires policy makers to take note and implement strategies which could make a difference to the health of the population.” – Charlotte Marris

 

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“This is a good, competent study. It provides pretty solid evidence that there’s a correlation between the levels of two air pollutants (fine particulates, that is, fine dust as measured in a particular way, and nitrogen dioxide) and changes in the heart that might lead later to heart failure. But a study like this can’t tell us everything. Heart disease is affected by a wide range of factors – smoking, drinking alcohol, diet, exercise, social position, and more.  Suppose that people whose heart health is worse because of some of these factors also are more likely to live in places where air pollution is high. That could show up as a correlation between air pollution and heart disease, even if the pollution itself is having no direct effect on the heart. In this study, the researchers made great efforts to allow for possible confounding factors like this, by adjusting for them statistically – but even though they did a good job on this, doubts about what causes what can never be eliminated from an observational study like this. Another limitation is that the researchers had no data on exposure to pollution inside the home, or at work, so they could not make adjustments for these. Also, the research could not look at possible effects of air pollution many years ago on people’s heart health now, because the participants were not followed up over a long period of time. Someone who lived in a very polluted area most of their life, but moved to a cleaner spot just before the study started, would look to the researchers just like someone with the same characteristics who had lived in cleaner air all their life.

“There are also some questions about how typical the participants were of people in the UK in general. People in the UK Biobank cohort do differ from UK averages in several ways. Also, for the purposes of this study, the researchers did not use data from people who moved house between the time when basic data on them was collected and the time a few years later when the measurements of their hearts were made, and they did not use data from people with pre-existing cardiovascular disease. Those exclusions are necessary for this study, but they do make the people studied less typical of the UK population as a whole, and therefore make it a little harder to conclude that the findings are broadly typical. Nearly 15% of the original list of participants had to be left out because they had changed their address – maybe people who move tend to be different from those who don’t. And, interestingly, the person (Mya Steer) whose experience is reported in the press release could not have been included in the study because of her pre-existing heart disease – so this study actually tells us nothing direct about possible effects of air pollution on people like her.

“Even though I can’t be sure from this study that these air pollutants do actually cause these potentially harmful changes to the heart in the ways described in this study, I think there is good evidence that these pollutants do have real effects on heart health. My opinion is based on results from many other studies, not just this one, and though most of them were also observational, the evidence for the relationship being one of cause and effect does gradually add up. More research is needed on exactly how the pollutants cause harm, and that might lead to ways of reducing the harm. But clearly it’s important to look at how the levels of these air pollutants can be reduced. This isn’t as straightforward as is sometimes thought. The press release says that 20-30% of UK outdoor air pollution is due to road transport – but that means that 70-80% of it is not due to road transport and we aren’t going to be able to deal with the issue by looking only at roads. Even on the roads, the pollution doesn’t all come from fuel burning. Despite various problems like the scandals about pollution from Volkswagen and other cars, pollutant levels from diesel vehicles have been falling fairly fast, and already a big proportion of the particulate (fine dust) pollution from roads actually comes from dust from tyres and brakes, and from passing vehicles stirring up the dust that is already on the road. Changing to electric vehicles will reduce some pollutants, but won’t have much effect on these sources that have nothing to do with fuel. So effective action to reduce harms from outdoor air pollution will have to involve changes of many different kinds, not just to road fuels.”

 

* ‘Association between ambient air pollution and cardiac morpho-functional phenotypes: Insights from the UK Biobank population imaging study’ by Aung et al. published in Circulation aon Friday 3rd August.

 

Declared interests

Prof Kevin McConway: “Kevin McConway was the lead author of a chapter on Measurement and Communication of Health Risks from Pollution for the 2017 Annual Report of the Chief Medical Officer ‘Health Impacts of All Pollution: what do we know?’. He is a member of the Science Media Centre’s Advisory Committee.”

None others received.

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