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.

To the Editor: Health professionals in the Sydney Greater Metropolitan Region have been found to be less aware of air pollution and its health effects than are patients susceptible to such effects.1 Therefore Sharman’s brief review of the harmful effects of air pollution is welcome.2

In offering advice on how to minimise the exacerbation of pollution-induced harm by exercise, Sharman concentrates on the spatial distribution and temporal variation of traffic. The advice is sound for the metropolitan population, but incomplete for non-metropolitan residents exposed to smoke from burning biomass.

Australia’s National Environment Protection Measure defines limits for inhalable particulate matter suspended in ambient air (PM10). The NSW Department of Environment and Conservation operates a network of monitoring stations to measure PM10 and other pollutants, and posts the results daily on its Internet site <www.epa.nsw.gov.au/index.htm>. The National Environment Protection Measure requires environmental authorities to work towards reducing the number of days on which PM10 exceeds the daily limit to no more than 5 days per year. This goal is far from being realised in some places.

One such place is Wagga Wagga, NSW, where monitoring of PM10 started on 11 April 2001. From that date up to 6 July 2005, the city experienced 118 days on which PM10 exceeded the limit, as well as many days of pollution near but below the limit. In the same period, monitoring stations in the Sydney Greater Metropolitan Region registered between 11 and 33 days of excess PM10.

Of the 118 days of above-limit PM10 in Wagga Wagga, 30 occurred in the period from 30 October 2002 to 26 January 2003, when there were severe bushfires in south-eastern Australia. Most of the rest had a cause that is very evident in the surrounding countryside in autumn — the burning of paddocks to prepare them for sowing.

Rural residents’ health is worse than urban residents’ health for many reasons, but biomass burning is not widely recognised as one of them. The Australian Medical Association’s Rural Reference Group, which is being convened to improve rural health,3 may wish to add environmental health to its agenda.

There are two steps that the Group could take to lessen the effects of smoke from burning biomass. The first is to acquaint rural doctors with information such as that presented by Sharman. The second is to persuade the Department of Environment and Conservation and NSW Health to issue rural health warnings based on the continuous, real-time output of PM10 monitors in regional centres.

In reply: As emphasised in my editorial, regular aerobic exercise is to be encouraged, as it is of undeniable benefit to health.1 The crux of the intended message was for people to undertake an exercise program, but not near busy roads. There was no suggestion to curtail outdoor activities.

Although the effect of traffic pollution on an individual is not well understood, there are many hundreds of scientific papers consistently finding that whole automotive pollution, or components thereof, damage biological tissue and promote disease.2 The World Health Organization recognises urban air pollution as a major risk to human health, with exposure to particulate matter alone accounting for an estimated 800 000 deaths a year globally.3

Would it be ethical to confine this information to the annals of scientific literature, or should some attempt be made to inform those who may be unknowingly and unnecessarily exposing themselves to veritable risk? People should have access to all the available information so that they can make an informed decision on where to exercise. Not only is it common sense, but it is entirely reasonable to suggest that people would be better off avoiding exercise alongside roadways congested with traffic.

Quite separate to the question of exercising beside busy roads, but equally important from a health perspective, is the issue of persistently high ambient levels of particulate air pollution in certain regions. The air quality problem encountered in Wagga Wagga is exacerbated by geographical and climatic factors that encourage entrapment of air pollution, owing to a temperature inversion layer that is particularly apparent during winter. Other cities, such as Launceston, Tasmania, suffer the same fate and, in both cases, smoke from domestic wood-heaters is thought to be the biggest contributor to poor air quality.

What are people to be told regarding exercise in these regions? It may be reasonably argued that habitual exercise in such environments would be detrimental to health, but it would be a very poor public health outcome if people were advised to stop exercising. In the affected areas mentioned, community education programs have been in existence for years, but these appear to be of limited value, as daily air pollution limits are regularly exceeded,4 as highlighted by du Plessis. Although unpopular, the answer lies in stricter regulations to clean the air, such as banning wood-heaters and tighter monitoring of rural burning.