A summer day, a leafy street, a bicycle. Under the right circumstances cycling can be a delight, and it’s universally recommended as a healthy physical activity. But because of the shared nature of most streets, vehicular traffic is often an inescapable part of the cycling experience. While bike-specific infrastructure can reduce the risk of collisions, automotive pollution doesn’t stop where bike lanes begin.

A 2011 study published in Environmental Health Perspectives, “Traffic-Related Air Pollution and Acute Changes in Heart Rate Variability and Respiratory Function in Urban Cyclists,” sought to examine the health effects experienced while cycling in traffic. The researchers, based at Health Canada, Environment Canada, and the University of Ottawa, looked at the relationship between automotive pollution and changes in measures of cyclists’ heart rate variability, a measure of cardiovascular health.

In the study, 42 healthy, nonsmoking adults cycled for an hour on both busy and quiet streets as well as indoors. Factors such as carbon black and volatile organic compounds were measured along each route and participants’ health was examined before and after cycling.

The study’s findings include:

• Exposure to heavy traffic significantly decreased heart-rate variability (HRV) in the cyclists for up to three hours after they finished cycling. Decreased HRV is associated with a higher risk of heart attacks.
• Increased levels of ultra-fine particles were associated with a significant decrease in the high frequency measure of HRV four hours after the start of cycling.
• Nitrous oxide levels were inversely associated with variation in heartbeat-to-heartbeat intervals two hours after the start of cycling.
• Ambient ozone levels were inversely associated with heartbeat-to-heartbeat intervals three hours after the start of cycling.
• Levels of atmospheric volatile organic compounds were not associated with changes in HRV.

The researchers note that the study has some weaknesses, in particular the small sample size, but overall conclude that short-term exposure to automotive air pollution can contribute to changes in autonomic regulation of the heart. Because the health benefits of physical activity outweigh the risks, the researchers suggest, “When possible, it may be prudent to select cycling routes that reduce exposure to traffic.”

Drivers are not immune to the risks of breathing polluted air, of course. Another study in Environmental Health Perspectives, “Air Pollutants from Automotive Traffic Act on Glutamatergic Neurons,” showed that ultrafine particles, which easily pass through car air filtration systems, can cause brain neurons to show of signs of inflammation associated with premature aging and Alzheimer’s. And for drivers, unlike cyclists, not being in traffic isn’t an option.

Tags: bicycling, bicycle, bikes, safety, pollution, cars

By Leighton W. Klein | July 14, 2011