Clinicians prescribing exercise: is air pollution a hazard?

To the Editor: The editorial by Sharman about exercise and air pollution1 makes the point that cars contribute substantially to air pollution, and air pollution is known to have adverse health effects. Therefore, Sharman posits that exercise, which is unequivocally good for human health, is best done away from sources of air pollution.

This “common-sense” maxim to avoid air pollution when exercising is superficially reasonable as far as it goes, but is a very weak response to the health and social problems generated by motor vehicles or the need for increased levels of physical activity in the population. With only half the Australian population achieving adequate levels of physical activity,2 recommendations to patients to be more physically active are essential. To simultaneously promote exercise and then put a health warning on this physical activity effectively undermines the recommendation.

Part of the difficulty in judging the actual risks from air pollution and benefits of physical activity is that the science of pollutant exposure is not well understood at the individual level. It is not currently possible to say that exercising in a particular environment will have a net negative effect. Thinking laterally, perhaps physical activity even boosts the immune response in a way that helps the body resist adverse effects of air pollution? Perhaps only under more extreme conditions would outdoor activities need to be curtailed.

One body of relevant research that Sharman did not consider is the research on pollutant exposure by travel mode, which clearly indicates that car drivers and passengers have pollutant exposures at least twice that of pedestrians walking on the same street.3,4 The longer people sit in cars, the greater their exposure to air pollutants, not to mention the increased risk of obesity.5 Therefore, a highly sensible approach is to recommend to patients that they avoid travelling in cars, particularly if the patient is sensitive to air pollutants or if traffic is congested.

The most obvious common-sense solution to reduce air pollution and increase individual and population levels of physical activity is to recommend to patients that they replace short car trips with walking or cycling. As little as two 15-minute active transport trips per day can achieve recommended levels of physical activity to maintain health. It is possible to change travel behaviour, and this is a far better recommendation for all patients than telling them not to exercise near traffic.