Traffic pollution seen as a major contributor to new asthma cases

By the time you've finished reading this sentence, you've likely taken two breaths and inhaled about two litres of air. In a day, the average person will breathe in about 20,000 litres.

Consider the amount of pollution that air contains and it's easy to imagine how ill you can become from just breathing. It's no surprise, then, that air pollution is a major contributor to asthma, the most common chronic disorder in children.

Almost half of all children have at least one episode of wheezing before six years of age, according to a report which was published in The Lancet to coincide with World Asthma Day last week. Forty-eight per cent of children under five years of age with asthma report an attack in the preceding year, a rate higher than any other age group.

In Hong Kong, more than 330,000 people suffer from asthma, according to 2011 figures from the Hong Kong Thoracic Society. About 8 per cent of primary students aged six to seven years, and 10 per cent of secondary students aged 13 to 14 years, have asthma. Every year, about 70 to 90 people in the city die from asthma attacks; among them, 20 to 30 people are aged between 15 and 44.

Evidence from studies during the past several decades makes it clear that air pollution can exacerbate pre-existing asthma. But recent research suggests that air pollution might cause new-onset asthma as well, say the authors of The Lancet report, professors Michael Guarnieri and John Balmes, of the University of California, San Francisco.

Reviewing studies from the past five years since 2009, the authors show that short-term exposure to ozone, nitrogen dioxide, sulphur dioxide, PM2.5 particulate matter and traffic-related air pollution can increase the risk of exacerbations of asthma. They also found that long-term exposure to air pollution, especially from traffic, can lead to new cases of asthma in adults and children.

A study of 10 European cities published last year in the European Respiratory Journal estimated that 14 per cent of chronic childhood asthma is due to exposure to traffic pollution near busy roads.