How pollution cancels cardiovascular benefits

Exposure to traffic fumes may negate any heart and lung benefits of walking among older adults

A new UK study examined how even short-term exposure to tiny particles of soot or dust in traffic fumes can affect the arteries and lungs – and the research is likely applicable to Australia, says one expert.

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

“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,” says senior author Professor Fan Chung from the National Heart & Lung Institute at Imperial College London, UK.

“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.”

In the UK, polluted air contributes to about 40,000 deaths a year, nearly a quarter of them in London. Air pollution is responsible for around 5.5 million premature deaths worldwide each year.

Earlier research shows that exposure to fine particulate matter (with a diameter of 2.5 micrometers or less; PM2.5) found in diesel exhaust fumes increases the risk of cardiovascular disease and death, and can reduce lung function, particularly in the elderly and those with chronic obstructive pulmonary disease.

The Lancet study included 119 adults aged 60 or over, including 40 healthy volunteers, 40 with stable COPD and 39 with stable ischaemic heart disease. All participants had abstained from smoking for the past 12 months, and continued any medications as usual throughout the study.

Participants were randomly assigned to spend two hours walking along the western end of London’s Oxford Street, an area where traffic is restricted to diesel-powered buses and cabs; or through a traffic-free area of the city’s Hyde Park.

Three to eight weeks later, the participants swapped routes.

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.

However a walk along 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 health impact of pollution was particularly marked in participants with COPD, who experienced a narrowing of the small airways—reporting more respiratory symptoms including cough, sputum production, shortness of breath, and wheeze—and increased arterial stiffness after walking in Oxford Street compared with Hyde Park.

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

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, suggesting that these drugs might have protective effects.

The authors say more research is needed to confirm this finding. They also point out that there was no resting control group, so they can’t be sure that walking contributed to the changes in lung function and arterial stiffness, although previous studies have shown that walking improves arterial stiffness.

 “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,” says Prof Chung.

“Our study provides a clear message to improve the quality of the air we all share,” the authors conclude.

“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.”

Dr Gayan Bowatte, from the Melbourne School of Population and Global Health at The University of Melbourne, says the findings are relevant to Australia.

“These results confirm our findings generated using observational Australian studies where we investigated both short and long term exposure to traffic related air pollution,” Dr Bowatte says.

“Our research conducted within the Tasmanian Longitudinal Health Study and published in Journal of Allergy and Clinical Immunology and European Respiratory Journal found that NO2 exposure and living close to a busy road cause adverse respiratory effects in middle-age adults.

“The highest recoded mean annual NO2 in our studies was 23 ppb, which was a relatively low level compared to South East Asian countries. Nevertheless, our studies found that even these relatively low levels were associated with increased risk of adverse adult lung health outcomes such as asthma and poor lung function.

“The findings from recent Lancet paper are relevant to Australia since some of our busy roads may fall within the poor air quality observed in Oxford Street, London.”

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