Urban cyclists breathe in more than twice the amount of harmful soot pedestrians do says London study

Cyclists in London and other large cities inhale more than 2.3 times more black carbon soot than pedestrians according to new reasearch carried out by Barts and The London School of Medicine.

Inhalation of the tiny soot particles expelled by cars, buses and lorries is increasingly being associated with a wide range of health effects including heart problems and impaired lung function.

The London study led by Proffessor Jonathan Grigg aimed to find out whether cyclists had a greater exposure to black carbon and whether the way healthy adult cyclists commute to work increases their exposure.

To do this researchers compared the lung dose of black carbon in a sample of five healthy non-smoking urban cycle commuters and five healthy non-smoking urban pedestrians all between the ages of 18 - 40. To measure lung dose the researchers sampled lower airway cells called airway macrophages - specialised cells that sit on the airway surface and ingest foreign material. Analysis of these microphages showed that the cyclists had 2.3 times more black carbon in their lower lungs compared with the pedestrians.

"The results of this study have shown that cycling in a large European city increases exposure to black carbon. This could be due to a number of factors including the fact that cyclists breathe more deeply and at a quicker rate than pedestrians while in closer proximity to exhaust fumes, which could increase the number of airborne particles penetrating the lungs, said Dr Cinedu Nwokoro one of the researchers involved in the study.

The London study, will be presented to presented to the European Respiratory Society's Annual Congress and although it was based on a small sample of adults it does in some ways echo the findings of a Canadian study published earlier this year in the journal Environmental Health Perspective which found evidence of short term heart irregularities in cyclists exposed to high levels of air pollution.

However, the scientists behind behind the Canadian study which itself was of a relatively small sample size were careful not to strike an alarmist note saying simply:

"When possible it may be prudent to select cycling routes that reduce exposure to traffic and/or to avoid cycling outdoors or exercise indoors on days with elevated air pollution levels."

While any threat to health is a cause for concern most researchers stress that not cycling is not the answer to the problem – reducing exposure to pollutants and understanding the risks of different transport choices is. While the London study suggests cyclists breathe pollutants in more deeply, Danish research suggests that car occupants are exposed to up to four times the levels of pollutants that cyclists are.

According to researchers on both studies lowering exposure to pollutants should be a consideration for cyclists when planning their routes and more importantly still for those that build cycling infrastructure. London's network of Barclays Cycle Superhighways are either along or adjacent to exactly the sorts of roads that both the London and Ottowa studies suggest cyclists should avoid.

There is as yet no study into levels of heart or lung impairment amongst populations of cyclists with a correlation to historic levels of air pollution (although there is surely population-wide data on countries like the Netherlands which has high levels of cycling amongst it's population). In the meantime most researchers seem to agree that the positive health benefits of cycling outweigh the negative effects of breathing in pollutants. Although Dr Nwokoro of the London research team and an active cyclist appeared to hedge his bets somewhat in a press release put out by the European Lung Foundation announcing the new research: "Our data strongly suggest that personal exposure to black carbon should be considered when planning cycling routes. Whether cycling by healthy individuals is in itself associated with adverse health effects is currently being assessed in a larger ongoing study."

The Canadian study, Traffic-Related Air Pollution and Acute Changes in Heart Rate Variability and Respiratory Function in Urban Cyclists, which took place last year in Ottowa involved 42 healthy cyclists wearing heart rate monitors and riding for an hour on busy and quiet roads while an instrument in their cycle panniers measured levels of atmospheric pollution. According to researchers the results of the study suggest that short term exposure to pollutants, particularly fine soot particulates, nitrous oxide, and ozone increased heart rate variability for up to 3 hours after riding. That's not a good thing because increased heart rate variability reduces the heart's ability to deal with stress. On the other hand, you might expect that cyclists will have stronger hearts in the first place.

The suggestion from other researchers quoted in a Scientific American article on the Ottowa study is that close proximity to fine soot particles by being too close to the exhaust pipe of the vehicle in front may be part of the problem – as the soot particles move further away from the exhaust pipe they clump together to form larger particles that are less likely to be breathed deeply in to the lungs. So the suggestion is that cyclists keep at least 15 feet between themselves and the backs of vehicles belching out exhaust fumes. US researchers say moving to the side in to a segregated bikes lane is better still, as is filtering up to the front of traffic queues to take advantage of advanced stop lines. Physically segregating cycle lanes from the traffic has even more of an impact as does choosing a less busy route.

The bottom line is that all city dwellers are exposed to raised levels of pollutants, how these affect your body and how great your exposure comes down to how fit you are, your chosen mode of transport and very probably your genetic susceptibility to various combinations of pollutants in differing concentrations over prolonged periods of time. Less pollution is the answer and in the meantime just move back a bit from that exhaust pipe.