Even Low-Level Air Pollution Found to Cause Heart Damage

Nicky Broyd

August 03, 2018

New UK research has found a clear association between air pollution and the development of larger right and left ventricles in the heart, similar to that seen in the early stages of heart failure.

Most of the 3920 middle-aged participants analysed for the research lived outside major UK cities often associated with high air pollution levels but the scientists found that even people exposed to air pollution levels well within UK guidelines showed changes to the structure of their heart.

The findings have been published in the journal Circulation.

In the UK more deaths are believed to be caused by air pollution than road traffic accidents.

The Study 

The research was a collaboration between Queen Mary University of London and the University of Oxford.

Scientists, led by Professor Steffen Petersen from Queen Mary University of London, studied data from participants in the UK Biobank study.

Their aim was to investigate the relationship between chronic past exposure

to traffic-related pollutants and cardiac chamber volume, ejection fraction and left ventricular remodelling patterns, after accounting for potential confounders.

Participants underwent blood tests and health scans. Cardiac magnetic resonance imaging (MRI) was used to measure the size, weight and function of their hearts at fixed times.

The studied cohort was free from pre-existing heart disease, had a mean age of 61.7 years and 45.6% were men.

The research was part-funded by the British Heart Foundation.

Findings

There was a clear association between those who lived near loud, busy roads, and were exposed to nitrogen dioxide (NO2) or fine particulate matter (PM2.5) – and the development of larger right and left ventricles.

The authors write that PM2.5 concentration was significantly associated with larger left ventricular end-diastolic volume and end-systolic volume.

Similarly, higher nitrogen dioxide (NO2) concentration was associated with larger right and left ventricular volume.

In the study, average annual exposures to PM2.5 (8-12µg per cubic metre) were well within UK guidelines (25µg per cubic metre), although they were approaching or past World Health Organization (WHO) guidelines (10µg per cubic metre). The WHO has said that there are no safe limits of PM2.5.

The participants' average exposure to NO2 (10-50µg per cubic metre) was approaching and above the equal WHO and UK annual average guidelines (40µg per cubic metre).

Strengths and Limitations

The study, 'Association between ambient air pollution and cardiacmorpho-functional phenotypes: Insights from the UK Biobank population imaging study', had a number of strengths – it had a large sample size, accurate and reproducible measurements by cardiac MRI imaging and uniform data collection protocols.

However, it also had limitations – it estimated outdoor pollution levels at participants' homes, did not take into account things like the time spent at home or in traffic, indoor air pollution or workplace exposure.

Modifiable Risk

The study authors say: "The association between ambient air pollution and adverse cardiac phenotypic changes in individuals without prevalent cardiovascular disease suggests that air pollution should be recognised as a major modifiable risk factor which needs to be targeted via public health measures."

Dr Nay Aung from Queen Mary University of London, lead author who led the data analysis, said in a news release: "Although our study was observational and hasn't yet shown a causal link, we saw significant changes in the heart, even at relatively low levels of air pollution exposure. Our future studies will include data from those living in inner cities like Central Manchester and London, using more in-depth measurements of heart function, and we would expect the findings to be even more pronounced and clinically important."

Dr Holly Shiels, reader in physiology at the University of Manchester, commented on the findings: "The association[s] 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."

Prof Kevin McConway, emeritus professor of applied statistics at the Open University, said that although this appeared to be "good, competent" research, "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."

Professor Jeremy Pearson, associate medical director at the British Heart Foundation, commented: "What is particularly worrying is that the levels of air pollution, particularly PM2.5, at which this study saw people with heart remodelling are not even deemed particularly high by the UK Government – this is why we are calling for the WHO guidelines to be adopted. They are less than half of UK legal limits and while we know there are no safe limits for some forms of air pollution, we believe this is a crucial step in protecting the nation's heart health."

Author Steffen E. Petersen provides consultancy to Circle Cardiovascular Imaging Inc, Calgary, Canada. Other authors have no conflicts of interest to declare.

Association between ambient air pollution and cardiac morpho-functional phenotypes: Insights from the UK Biobank population imaging study, Aung et al. 3 Aug 2018Circulation. 2018;0:CIRCULATIONAHA.118.034856. Abstract.

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