Air pollution cancels out benefits of exercise

DANIEL LEAL-OLIVAS via Getty Images

Traffic pollution poses health risks for older people and unborn babies according to two separate studies published today. They also occur among healthy people, the study found. However, it is still a notorious area for dirty air, with high levels of black carbon, nitrogen dioxide, and fine particulate matter.

The study, in the Lancet medical journal, warned breathing in pollution from diesel cars is particularly unsafe.

An analysis of the data found that increases in traffic-related air pollutants were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age. 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.

The project was also supported by the UK Natural Environment Research Council, the Medical Research Council, the Economic and Social Research Council, the Department of Environment, Food and Rural Affairs, and the Department of Health.

"The findings suggest that air pollution from road traffic in London is adversely affecting foetal growth", the study's authors concluded.

The researchers from Imperial College London and Duke University in the U.S. recruited 119 people for the study who were either healthy, had stable heart disease, or stable chronic obstructive pulmonary disease (COPD) - a type of lung disease.

The volunteers were asked to take two-hour walks at midday in two London settings: a busy section of Oxford Street (which regularly exceeds global air quality limits) and a relatively quiet, traffic-free area of Hyde Park.

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 the blood vessels could expand.

Noise and air pollution in both of the settings were also measured at the times of the walks.

Participants spent two hours walking along traffic-heavy Oxford Street, which is one the most polluted spots in the United Kingdom, or in Hyde Park.

Their stride through a quiet section of Hyde Park had a positive impact on the heart and lungs, but a similar level of exercise in Oxford Street had a minimal effect on health.

While people doing the park walk had increased blood flow and their arteries became less stiff by 24% in some cases, the Oxford Street walkers saw barely any improvement, with just a 4.6% improvement for healthy volunteers.

By comparison, a walk up and down Oxford Street led to only a small increase in lung capacity in participants - far lower than recorded in the park.

Although the team noted that stress could be a contributing factor, with the increase in noise and the number of people on Oxford Street another reason behind the physiological differences observed, the new findings still add to the growing body of evidence on the dangers of urban air pollution.

"About 17 million babies worldwide live in areas where outdoor air pollution is six times the recommended limit, and their brain development is at risk, the United Nations children's agency (UNICEF) said on Wednesday..."

"For many people, such as the elderly or those with chronic disease, very often the only exercise they can do is to walk", said Kian Fan Chung, professor of respiratory medicine at the National Heart and Lung Institute at Imperial and lead author of the study.

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