Study: Bicyclers Inhale Tailpipe Pollution

Photo: Mario Tama/Getty Images

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For the first time, cycling in heavy traffic has been linked to a heart health risk, Canadian researchers reported last month. A new study found cyclists in Ottawa, Ontario, had heart irregularities in the hours after their exposure to a variety of air pollutants on busy roads.

The study does not suggest that bikers would be better off driving; the health benefits of cycling far outweigh the risks from air pollution and traffic collisions relative to car driving, and drivers are exposed to more pollution in stop-and-go traffic, according to other studies. Rather, the findings point to simple solutions for a cleaner ride, such as these:

• Avoid bicycling on busy roads;
• Separate bike lanes from busy roads by as much as a block, as one study suggested, or by something as simple as planters, as a study in Portland, Ore. suggested, to reduce pollution levels around bicyclers;
• Provide "bicycle boxes" or other designated areas that separate bicyclists from idling cars at traffic lights and intersections.

For the study, 42 healthy, non-smoking cyclists wore heart monitors before, during and after cycling for one hour on high- and low-traffic roads between May and September last year. Instruments on the bikes' panniers measured exposure to air pollution.

Short-term exposure to pollution in heavy traffic — like ultrafine particles, nitrogen dioxide or ozone — significantly decreased heart rate variability in the cyclists for up to three hours after they finished cycling. Experts say reduced heart rate variability is associated with a higher risk of heart attacks.

"A very healthy person is like a Ferrari. Step on the gas and it really goes fast. Step on the brakes and it really slows down. The human heart, you want it to be like that too," said Arden Pope, an expert in the health effects of air pollution and professor at Brigham Young University in Provo, Utah. With lower heart rate variability, the heart is behaving more like a minivan than a Ferrari, Pope said, meaning that it is less able to respond to stress.

Researchers are not sure how air pollution alters heart rate variability, Pope said. One idea is that particles in the lungs cause inflammation, which throws off the body's ability to carry out its automatic functions. No respiratory effects were found in the cyclists. The researchers did not find any significant changes in their lung function, probably because all the cyclists were healthy, and most had no asthma or other respiratory problems.

Around the world, researchers have found that whenever fine particles increase in the air, deaths and hospitalizations from asthma, heart attacks and other cardiopulmonary problems increase, too. Hours to weeks of exposure to particles that are smaller than 2.5 micrometers in diameter, which peak during rush hours, can trigger cardiovascular effects, according to the American Heart Association.

"The closer you are to the source of the fresh exhaust, the worse it is," said Patrick Ryan, an environmental epidemiologist at the University of Cincinnati, who studies the health effects of traffic-related pollution.

Near the tailpipe, these particles are small enough to lodge deep in the lungs, triggering heart attacks and hospitalizations from lung diseases such as asthma. Tiny particles can also cross the blood-brain barrier, potentially harming the nervous system. Farther away from the tailpipe, these particles clump together, growing too large to lodge deeply, Ryan said.

That's why even a small separation from cars, created by physical barriers to traffic is important for cyclists.

"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," the research team wrote.

This is an edited version of "Exhaust-ing ride for cyclists: Air pollutants trigger heart risk", which first appeared in Environmental Health News. It is republished with permission.

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