AIR POLLUTION and CYCLING
While the health benefits of exercise via cycling are estimated to substantially exceed any health impacts related to air pollution exposure or injuries from traffic collisions, cyclists are known to experience elevated exposures to traffic-related air pollutants. In addition, our research on cycling motivators and deterrents identified traffic-related air pollution exposure and traffic as major factors influencing the choice to make a trip by bicycle. This article in the Huffington Post outlines the issues well.
The Cycling in Cities team investigated the relationship between traffic-related air pollution exposure and respiratory and cardiovascular health impacts in commuting cyclists.
Study objectives were to:
- measure commuting cyclists’ exposure to traffic-related air pollutants (PM 2.5, PM10, ultrafine particulate) while cycling along two different bicycle routes in the city of Vancouver;
- estimate the pollutant dose received by each cyclist by accounting for changes in breathing rates, and related this to the health effects observed; and
- determine if there was a change in lung function, endothelial function (a measure of the health of the cells that line the inside of blood vessels), measures of inflammation (C-reactive protein, Interleukin-6), and a measure of oxidative stress (8-hydroxy-2′-deoxyguanosine) related to the level of air pollution exposure and estimated pollutant dose.
This study used a randomized (single) blinded crossover design. Each subject bicycled along two separate routes, while air pollutant levels along each of the routes were measured. Before and after each cycling session, subjects’ lung function and endothelial dysfunction were measured and a blood sample was collected. While cycling, subjects wore a heart rate monitor, and a cycling computer measured and recorded their work rate. At the end of each cycling session subjects’ minute ventilation was measured and related to their heart rate and work rate by cycling in the laboratory on a stationary bike while breathing into a respirometer. This helped us understand how much the cyclist breathed at different levels of effort throughout the ride. The health endpoints were endothelial function, lung function and markers of inflammation.
In comparisons of health indicators after cycling downtown (higher traffic) versus along the residential routes (lower traffic), endothelial function was found to be on average 21% lower after cycling on the more polluted downtown route. Females and older participants experienced larger decreases. Endothelial function improved after cycling on the residential route. None of the other measures were different between the two routes. Although, the downtown route had levels of ultrafine particles ~ 60% higher than the residential route, other factors – besides air pollution – may have been responsible for the effects on endothelial function. Cycling increased breathing rates by 3.5 times compared to at rest.
Active transportation is a non-polluting form of transportation, and is increasingly encouraged by public health agencies as a way to improve air quality as well as physical fitness. While exercise is promoted as healthy behaviour, cyclists may experience higher doses of air pollution compared to other transportation modes due to their elevated breathing rates and cycling in proximity to traffic, especially during periods of elevated air pollution.
Interestingly, although ultrafine particle exposures and intakes were higher along the downtown route, the lack of association between air pollutant exposure or intake with endothelial function and other measures suggests that other factors on the downtown route may have influenced endothelial function.
The information from this study may be useful for providing advice to the public regarding about where and when to cycle (or where to reduce motor vehicle traffic) in order to achieve health benefits while at the same time minimizing potential adverse impacts related to air pollution exposure.
In another study focused more on climate, we used data from the 2003 Canadian Community Health Survey and Environment Canada to test whether cycling rates in Canadian cities were affected by climate, demographics, or population. The figure below shows the proportion of people in each city* who reported bicycling in a typical week, data for Canadian cities with at least 50,000 people.
*Note that, in the Canadian Community Health Survey, cities are not identified directly via political boundaries, but via Health Regions.
Conclusions: Bicycling patterns are associated with individual demographic characteristics and the climate where one lives. This evidence might be useful to guide policy initiatives for targeted health promotion and transportation infrastructure.
- [Article] Winters, M., Friesen, M. C., Koehoorn, M., & Teschke, K. (2007). Utilitarian bicycling: a multilevel analysis of climate and personal influences. American journal of preventive medicine, 32(1), 52-58.
- [Article] Cole, C. A., Carlsten, C., Koehle, M., & Brauer, M. (2018). Particulate matter exposure and health impacts of urban cyclists: a randomized crossover study. Environmental Health, 17(1), 1-14.