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London air pollution cancels positive health effects of exercise in over 60s

6 Dec 2017

Exposure to air pollution on city streets is enough to counter the beneficial health effects of exercise in older adults, according to new research. The study is one of two new studies led by scientists from the MRC-PHE Centre for Environment and Health at Imperial College London and King's College London.

In the first study, published in The Lancet, researchers recruited 119 volunteers over the age of 60 through the Royal Brompton Hospital, who were either healthy, had stable chronic obstructive pulmonary disease (COPD), or stable heart disease. The volunteers walked for two hours in two London settings at midday: in a relatively quiet part of leafy Hyde Park and along a busy section of Oxford Street, which has regularly breached air quality limits set by the World Health Organization.

Physical measurements were taken before and after the walks to show the effects of the exercise on cardiovascular health, including measurements of lung volume exhaled, blood pressure, and the degree to which their blood vessels could expand.

Analysis revealed that all participants benefitted from a stroll in the park, with lung capacity improving within the first hour and a significant lasting increase for more than 24 hours in many cases. By comparison, a walk along Oxford Street led to only a small increase in lung capacity in participants, far lower than recorded in the park.

Blood flow also increased after exercise, with decreases in blood pressure and an increase in heart rate. Arteries became less stiff in those walking in Hyde Park with a maximum change from baseline of more than 24% in healthy and COPD volunteers, and more than 19% in heart disease patients.

This effect was drastically reduced when walking along Oxford Street, however, with a maximum change in arterial stiffness of just 4.6% for healthy volunteers, 16% for those with COPD and 8.6% for heart disease.

Professor Fan Chung, senior author from the MRC-PHE Centre for Environment and Health, and the National Heart & Lung Institute at Imperial College London, said: “These findings are important as for many people, such as the elderly or those with chronic disease, very often the only exercise they can do is to walk. Our study suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic.

“It is possible that studies such as this could support new air quality limits, it shows that we can't really tolerate the levels of air pollution that we currently find on our busy streets. For people living in the inner city, it may be difficult to find areas where they can go and walk away from pollution, there may be a cost associated as they have to travel further away from where they live or work. These are issues that mean we really need to reduce pollution by controlling traffic. That should allow everyone to be able to enjoy the health benefits of physical activity in any urban environment.”

The authors add that it is possible that stress could account for some of the physiological differences seen between the two settings, with the increased noise and activity of Oxford Street having an effect. They also emphasise that while the study only involved two relatively short walks, the findings suggest that repeated exposures to air pollution would not be beneficial to our respiratory and cardiovascular systems.

The study was funded by the British Heart Foundation.

Air pollution linked to birth weight

A second study, led by another team of researchers from the MRC-PHE Centre for Environment and Health at Imperial College London, found that increases in traffic related air pollutants were associated with 2% to 6% increased odds of low birth weight, even after taking account of road traffic noise.

The study, published in the BMJ, used national birth registers to identify over 540,000 live, single, full-term births occurring in the Greater London area between 2006 and 2010. The mother’s home address at time of birth was recorded and average monthly concentrations of traffic related pollutants - nitrogen dioxide (NO2), nitrogen oxides (NOx), and fine particulate matter (PM2.5) from traffic exhaust and non-exhaust sources, such as brakes or tyre wear - as well as larger particulate matter (PM10) were estimated. Average day and night-time road traffic noise levels were also estimated.

Using statistical models to analyse the data, the researchers found that increases in traffic related air pollutants - especially PM2.5 - were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age, even after taking account of road traffic noise.

“With the annual number of births projected to continue increasing in London, the absolute health burden will increase at the population level, unless air quality in London improves,” the study authors conclude.

The findings held true after other potentially influential factors were taken into account, such as mother’s age, ethnicity and deprivation. However, an observational study cannot show a causal link between air pollution and birth weight and the authors also point to limitations, such as whether they have fully adjusted for deprivation.

The study was funded by the cross-research council Environmental Exposures & Health Initiative, led by the Natural Environment Research Council, in conjunction with the MRC, the Economic and Social Research Council, the Department of Environment, Food and Rural Affairs, and Department of Health.

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