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Traffic-polluted streets may negate benefits of walking in older adults, finds study in London

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Even short-term exposure to tiny particles of soot or dust found in traffic fumes on busy roads appears to thwart the benefits of walking on the heart and lungs of older adults, a study has found.

The effect was particularly marked in people with existing respiratory illness, said the researchers, suggesting clinicians should advice patients over 60 to avoid walking on streets with lots of traffic.

“We suggest that, where possible, older adults walk in parks or other green spaces away from busy roads”

Fan Chung

They analysed health impact of a walk through the traffic-polluted Oxford Street in London, compared to the city’s Hyde Park.

The study, funded by the British Heart Foundation and published in The Lancet, suggests that short term exposure to pollution is associated with stiffening of the arteries and impaired lung function.

The authors noted that polluted air contributed to 40,000 deaths each year in the UK, nearly a quarter of them in London.

They also highlighted earlier research showing the added dangers of exposure to the fine particulate matter – with a diameter of 2.5 micrometers or less; PM2.5 – found in diesel exhaust fumes.

It was found to increase the risk of cardiovascular disease and death, and can reduce lung function, particularly in the elderly and those with chronic obstructive pulmonary disease.

The new study involved 119 older adults aged 60 or over, including 40 healthy volunteers, 40 individuals with stable COPD, and 39 with stable ischaemic heart disease.

Aerial view of Hyde Park taken in 2011

Traffic pollution may negate benefits of walking in older adults

Source: BaldBoris

Hyde Park, London

They were randomly assigned to spend two hours walking along the western end of Oxford Street where vehicles are restricted to buses and cabs, or through a traffic-free area of Hyde Park.

Then, three to eight weeks later, participants did the other walk. All participants had abstained from smoking for the past 12 months, and continued any medications as usual throughout the study.

Levels of traffic-related air pollutants and measures of lung function and cardiovascular responses were taken before and during each walk.

In healthy participants, walking in Hyde Park led to an improvement in measures of lung capacity – average 7.5% increase in FEV1 – at five hours after the start of the walk – and arterial stiffness – 5% decrease in pulse wave velocity on average after three hours – that persisted for up to 26 hours.

In contrast, walking on Oxford Street led to only a small transient increase in lung capacity, and substantial worsening of arterial stiffness – average 7% increase in pulse wave velocity – associated with greater exposure to black carbon soot and ultrafine particles from diesel exhaust.

The detrimental effects of pollution were particularly marked in COPD patients who experienced increased arterial stiffness and a narrowing of the small airways – with more symptoms like cough, sputum production, shortness of breath and wheeze – after walking in Oxford Street than Hyde Park.

The harmful effects were associated with increasing exposure to black carbon soot and ultrafine particles, supporting the theory that fossil fuel combustion particles are particularly toxic to individuals with cardiovascular and lung disease.

Interestingly, further analyses found that pollution levels on Oxford Street resulted in worsening arterial stiffness in participants with ischaemic heart disease not using cardiovascular drugs, but had little effect on those taking medication.

This finding suggested that these drugs might have protective effects, said the study authors, though they noted that more research is needed to confirm this finding.

In the 78 walks involving the 39 participants with ischaemic heart disease, 49 walks were done with patients taking oral medication on that day, and the remaining 29 with participants not using drugs.

National Heart and Lung Institute, Imperial College London

Traffic pollution may negate benefits of walking in older adults

Kian Fan Chung

Senior study author Professor Kian Fan Chung, from the National Heart and Lung Institute at Imperial College London, said: “Our findings indicate that in traffic congested streets, like London’s Oxford Street, the health benefits of walking do not always outweigh the risk from traffic pollution.

“However, this should not be seen as a barrier to many older people for whom walking is the only exercise they do. We suggest that, where possible, older adults walk in parks or other green spaces away from busy roads”, he said.

Professor Chung added: “Our data indicates that taking medications which improve arterial stiffness such as statins, ACE inhibitors, and calcium channel blockers may well reduce the adverse effects of air pollution in individuals with ischaemic heart disease.”

In their study paper, the researchers concluded: “Our study provides a clear message to improve the quality of the air we all share. In London, the introduction of the low emission zone has had little impact on particulate matter levels.

“More radical solutions, such as recently announced to phase out diesel-powered black cabs and replace them with battery powered electric alternatives, are needed,” they said in The Lancet.

“Health professionals should make a reduction in public exposures to diesel particulate matter a high priority”

George Thurston and Jonathan Newman

In a linked comment in the same journal, Professor George Thurston and Dr Jonathan Newman, from the New York University School of Medicine in the US, said: “The changes in arterial stiffness reported in the study…are biologically consistent with the air pollution and CVD health associations found in the population-based studies of hospital admissions and mortality, further strengthening the consensus that the association between particulate matter and CVD is causal.

“Although more studies are needed on the respective health effects of all the individual constituents and sources of PM2.5, the results of this and other recent urban studies already indicate that policy makers and health professionals should make a reduction in public exposures to diesel particulate matter a high priority in PM2.5 air pollution control and patient avoidance strategies,” they said.

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