Clear The Air News Blog Rotating Header Image

December, 2005:

Dont run in smog

Dont run in smog

Monday, December 19, 2005

Letter to the South China Morning Post

We believe that many of your readers are interested in whether physical exercise in an environment of polluted air is harmful to health. We would like to follow up on the letter “Running in smog risky” (December 12), by Wong Chit-ming, Lam Tai-hing and Anthony J. Hedley, who suggested that there were no studies addressing this important issue.

Some years ago, we conducted an epidemiological study of the association between air pollution and cardiopulmonary fitness of primary-school children in Hong Kong. We showed that physical exercise was positively associated with cardiopulmonary fitness in those children who lived in and attended schools in the less-polluted district in our study, but not in children living and attending schools in the more-polluted district.

In other words, the beneficial effect of physical exercise that we all know seems to have disappeared among children exposed to an environment with high air pollution, in contrast to those living in a district of relatively clean air.

In our study, cardiopulmonary fitness was represented by “maximal oxygen uptake” – the maximum amount that a child can consume during maximum physical effort. The higher the oxygen uptake, the fitter the child. We estimated this parameter by an indirect method, using a standard test widely adopted in sports science. The study is called “Impact of air pollution on cardiopulmonary fitness in schoolchildren.”

Owing to limitations in the study design, our results could not demonstrate a definite cause-effect relationship, but the conventional wisdom that physical exercise is always beneficial to health must be questioned. Specifically, we consider it prudent to refrain from strenuous physical activity in highly polluted environments, for example, jogging on roads with moderate to heavy traffic. Moreover, the potential harm to the health of children playing in school grounds that are exposed to heavy traffic fumes should be urgently assessed.

WONG TZE-WAI and IGNATUS YU TAK-SUN, department of community and family medicine, Chinese University of Hong Kong

Running in smog risky

Running in smog risky

Monday December 12 2005

The answer to Rob James’ important question about the hazard of exercising in highly polluted air is potentially complex (‘Damage to exercisers?’, December 7). Research on this and related health issues is seriously hampered by lack of funding.

So far, on a whole-population basis, our analyses have shown that pollution causes large-scale harmful effects to health at all ages. Equally, they show that exercise is hugely protective to our health and prevents premature death. We have evidence that this protective effect operates for some even in the presence of air pollution.

But it is important to note that the large benefits of exercise are gained at relatively very low levels of activity. While athletes need to ‘regularly train and race outdoors’, doing this in highly polluted air will predictably cause an injury to heart, lungs and blood vessels. In susceptible individuals this could lead to acute adverse health effects. Children may be particularly vulnerable.

But those who take regular vigorous exercise are a highly self-selected group who are probably less likely to experience health problems in the short term. It is equally likely that many non-athletes limit their activity because they experience pollution-induced symptoms.

The benefits of exercise and good nutrition may mitigate these pollution-induced health effects, but we suggest there are no strong arguments for raising your ventilatory rate to very high levels in the air of the Pearl River Delta. Unfortunately, Hong Kong’s Air Pollution Index is of no help because most of the measured harm from pollution occurs well below the average level, where health effects are officially stated to be ‘not expected for the general population’.

CHIT-MING WONG, TAI-HING LAM and ANTHONY J. HEDLEY, department of community medicine, University of Hong Kong