The September 13, 2006 issue of the New England Journal of Medicine has a very interesting and unsettling paper on the deleterious coronary health effects associated with physical exertion in polluted environments (I learned about the paper from an AP story which includes helpful analysis from outside experts). Specifically, the paper studies the health effects of exposing 20 men with “stable coronary disease,” all over the age of sixty, to diesel exhaust while they exercise. The results:
Brief exposure to dilute diesel exhaust increases myocardial ischemia [angina] and impairs endogenous fibrinolytic capacity [the ability to clear clots] in men with stable coronary heart disease. Our findings suggest mechanisms for the observation that exposure to combustion-derived air pollution is associated with adverse cardiovascular events, including acute myocardial infarction [heart attack].
Before I jump to conclusions – and I will – I think it’s fair and worthwhile to consider comments on the limits of the study made in an editorial accompanying the NEJM paper:
… the study does not directly address the cardiovascular consequences of air pollution from sources other than diesel combustion. Furthermore, the findings can be directly applied only to men with a history of myocardial infarction and evidence of inducible ischemia on exertion. Nonetheless, if such exposures are causal, these findings may represent the tip of an iceberg constituting the effects of transient changes in exposure to elevated levels of air pollution on cardiovascular risk.
The editorial concludes:
The evidence … suggests that the risk of having an acute cardiovascular event triggered by vigorous exertion may be heightened with exposure to high levels of air pollution. Considering the unequivocal benefit of habitual exercise, including its established role in decreasing the risk that isolated episodes of exertion may trigger the onset of an acute cardiovascular event, the risk–benefit ratio may be optimized if people exercise away from traffic when possible.
This is not the first scientific study to connect air pollution to increased health risks. Indeed, the New England Journal of Medicine has covered this subject extensively, including papers on the long-term health effects of air pollution, and the deleterious influence of traffic on coronary health (including the heightened risk of heart-attack associated with riding a bicycle in traffic). But this new paper is significant in that it is the first controlled study of the short-term effects of air-pollution on an adult in the process of physically exerting himself. To be sure – as noted above – the study restricted itself to over-60 males with a history of heart disease. But, presumably, the physiological effects of the diesel fumes are measurable in younger, healthier (and female) bodies, too.
Now for the conclusion jumping. First, I should acknowledge that I have spent the better part of the last hour trying to figure out how and whether the diesel exhaust concentrations in the NEJM study have any relationship to standards and measurements of air quality in China. In this, I have failed; if anyone can help with insights on this subject, I will be very grateful and acknowledge the aid on this site.
In either case, I am going to take it on faith that the NEJM study used concentrations of diesel exhaust that are akin to those found in polluted urban environments — such as those found in Beijing, Los Angeles, Bangkok and other cities. If so – and this is a big if until I can figure out how applicable the NEJM study is – I think that there are three immediate conclusions:
1. The most important issue in any discussion of the Olympics and air quality must be the effect that polluted air will have upon the residents of Beijing before and after the games. I am keenly interested in how pollution will effect the performance of Olympic athletes, but I am even more keenly interested in how it will effect, say, the health of a Chinese migrant laborer on a busy road project that requires short-term physical exertions (for example, carrying heavy equipment).
2. Short-term visitors to China (or, for that matter, Los Angeles) need to take special care when exercising in traffic-heavy cities. I know of several Shanghai-area hotels that distribute “jogging maps” to guests; those maps tend to send joggers along traffic-heavy streets (such as the Bund) where diesel concentrations are quite high. At the very least, I think, the maps should include a warning of some kind.
3. I seriously doubt we are going to see strokes and heart attacks during Olympic events next August; modern Olympic athletes are too well-trained and monitored to succumb to catastrophic cardiac events, even during long events like the marathon. But I do think it’s time to acknowledge that athlete performance at the Olympics will be inhibited by air particulate pollution. During Beijing’s recent traffic experiments, air quality was improved, but not good (at least by the standards set by the US Environmental Protection Agency).
[On a personal note, during my recent trip back to clean-air Minnesota, I found that my endurance levels during exercise- as measured in my ability to run further - immediately rose by (an unscientifically measured) 20% - 30% (again, as measured in distances that I could run). And, upon my return to Shanghai, I found my endurance clipped quite quickly --- even though I work-out in an indoor gym. For what it's worth.]