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expert reaction to study looking at walking in a polluted street and a park, and cardiorespiratory health

The Lancet has published a study that analyses the health impact of a walk through Oxford Street in London, compared to Hyde Park.

 

Dr Marko Tainio, Senior Research Associate, MRC Epidemiology unit, University of Cambridge, said:

“This is a valuable study that increases our understanding of air pollution effects among older adults.  The authors are right to highlight that policies should aim to reduce air pollution, and noise, levels in streets to protect vulnerable population from potential harm.  For example, the planned removal of buses and taxis from Oxford Street should help to achieve this1.  However, it is important to remember the role that walking and cycling can play in helping to reduce air pollution and noise by removing motorized transport from the streets.

“It is also important to notice that this study looked at the short-term impacts, and, as authors commented, these findings need to be confirmed with empirical long-term studies examining trade-offs over months and years.  Based on our earlier modelling study, everyday walking and cycling would lead to clear health benefits for healthy adults in air pollution concentrations found in streets in London, even when the negative health effects of air pollution are taken into account2.  Also Professor Chung and colleagues noticed that health benefits of walking were reduced, not completely negated, among the healthy participants.

“The authors suggest that people should avoid walking in busy streets and should instead walk in parks or in green space.  We agree that this is good advice for recreational walking for people who can make that choice, but for people commuting or shopping, even in a city as polluted as London, we would still encourage walking and cycling.”

1 https://tfl.gov.uk/info-for/media/press-releases/2017/november/gla—consultation-on-major-transformation-of-oxford-street

2 ‘https://www.sciencedirect.com/science/article/pii/S009174351600040

 

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

“An important problem with most studies of the health effects of air pollution is that they are observational – that is, people are observed carrying out their normal activities.  In such studies it’s difficult or impossible to sort out whether bad health is actually caused by differences in pollution.  The people exposed to high levels of pollution may differ from the others in ways that have nothing to do with the pollution, and it could be these other differences that are causing any differences in health, and not the pollution at all.

“This very interesting new study gets round that limitation, by getting the participants to do things they wouldn’t necessarily have chosen to do as part of their normal activity.  That is, it’s a real experiment.  Another issue with studies of pollution and health is that people differ a lot from one another in the way their bodies respond to pollution, exercise, and just about everything else.  The ingenious design of this study gets round that by comparing each participant’s response to a walk along Oxford Street with the same participant’s response to walking in Hyde Park.  Therefore the research provides very good evidence that there is a real and substantial difference in people’s responses to taking a walk in these two places.

“What this doesn’t make clear is the extent to which the differences in response are actually due to differences in air pollution and traffic noise.  There are lots of differences between Oxford Street and Hyde Park apart from the levels of traffic and air pollution.  In case you haven’t been there, Oxford Street is a very busy city centre shopping street, completely built up, full of shops and rush.  Hyde Park is green, has beautiful trees, and is rather tranquil for a central London location.  Is it possible that the differences in response were caused by something other than the differences in air pollution and noise?  Perhaps it’s simply more relaxing to walk in the park.

“The researchers’ statistical analysis did deal with this issue.  They recorded the levels of important air pollutants, and noise, in both locations when individuals were walking, and they found evidence of some associations between the pollution measures and the health effects of the walks.  In other words, on average, respondents tended to experience better health effects from a walk when some pollutants were relatively low, compared to when they were high, even after allowing statistically for the fact that some walks were on Oxford Street and some in the park.  The measurement of these associations doesn’t benefit so much from the ingenious design of the study, in that each participant isn’t being compared with themselves in the same way, so we can’t be sure that all the differences in health impact between walking Oxford Street and Hyde Park are due to the differences in air pollution and noise.  The research does convince me, though, that poor air quality does play an important role in the short-term benefit one can get from taking a walk.  But perhaps that’s not all that’s going on, and I look forward to reading about future similar studies in other places.”

 

Prof. Ian Colbeck, Professor of Environmental Science, University of Essex, said:

“This paper highlights the risks to health by walking along polluted roads, for the over sixties with specific pre-existing medical conditions.  However we know from other research that for the vast majority of the population the benefits of any physical activity far outweigh any harm caused by air pollution except for the most extreme air pollution concentrations.  It’s important to that people continue to exercise.  In the UK physical inactivity is the fourth largest cause of disease and mortality and contributes to around 37,000 premature deaths in England every year.

“This study involved a limited number of participants and one location.  Ideally the work needs to be replicated with a larger cohort and a range of locations.

“What the report does confirm is the benefit of access to green space.  The link between green space and health was one of the reasons for the establishment of urban parks in the 19th century.  Beneficial effects of urban green spaces include improved mental health as well as reduced cardiovascular and respiratory mortality.

“This report comes days just after Sustrans concluded that more than 12,000 premature deaths would be prevented over the next decade if government targets for walking and cycling were met.”

 

Prof. Stephen Holgate, Special Advisor to the Royal College of Physicians on Air Quality, and MRC Clinical Professor at the University of Southampton, said:

“This is good quality research.  The data samples are on the small side (40 healthy volunteers, 40 individuals with COPD, and 39 with ischaemic heart disease), but the findings of differences across five time points adds robustness and confidence to the findings.  The study deliberately selected COPD and ischaemic heart disease at-risk patients.  Within these two groups, the differences, when they occurred during and after the exercise, are impressive and reassuring.  As far as I can tell, this is an experimental study using appropriate physiological measures of lung function and cardiovascular health.

“I believe we can be quite confident from this study that it is the pollution that is the factor responsible for changes in lung function – I am unable to see what confounding factors beyond drug treatment could have influenced the outcomes.  The findings that drug treatment prevented the CV changes is itself a very helpful ‘positive control’.

“Overall, the findings add to evidence of the importance of pollutant effects in vulnerable groups, and have implications for pollution in general from vehicles (diesel, petrol, brakes and tyres) as sources of pollutants.

“The observation that air pollution encountered on a high street in London removes any health protection produced by exercise outdoors is yet another demonstration that pollution is eroding the health of ordinary people.  More than this, it would seem that pollution, in large part related to traffic emissions, has an immediate adverse effect on those with chronic diseases such as COPD and cardiovascular diseases.  While medication for cardiovascular disease apparently protects against acute pollutant effects, is this the way we should be dealing with the problem?  I would say no!  This important study mandates action to radically reduce pollution at source to enable our cities and towns to be safe places to live in and move around.”

 

* ‘Respiratory and cardiovascular responses to walking down a traffic-polluted road compared with walking in a traffic-free area in participants aged 60 years and older with chronic lung or heart disease and age-matched healthy controls: a randomised, crossover study’ by Rudy Sinharay et al. published in the Lancet on Tuesday 5 December 2017.

 

Declared interests

Prof. Kevin McConway: “Kevin McConway is the lead author of a chapter on Measurement and Communication of Health Risks from Pollution for a forthcoming Annual Report of the Chief Medical Officer. He is a member of the Science Media Centre’s Advisory Committee.”

None others received.

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