Exhaust-ing ride for cyclists: Air pollutants trigger heart risk
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In big cities around the world, cyclists breathe an array of pollutants from exhaust-spewing cars. A new study has now found a link between cycling on high traffic roads and heart risks. Even healthy cyclists had harmful changes in their heart rates. Experts say cyclists should stick to their two-wheels, however, pointing to simple solutions to reduce exposure.
Unrelenting traffic leaves a wake of gritty exhaust for cyclists to breathe.
By Brett Israel
Environmental Health News
July 6, 2011
NEW YORK – Even by this city's standards, the Garment District is an imposing place to ride a bike.
A never-ending parade of delivery trucks rumbles along 8th Avenue between 34th and 42nd streets, leaving a wake of gritty exhaust for cyclists to feel, smell and breathe.
After riding in the Garment District, Robert "Rocket" Ruiz, a 13-year veteran of the bike messenger business, would often look into the bathroom mirror and see his face covered in grime.
"I remember having to wash my face three or four times a day," said Ruiz, now the head dispatcher for Quik Trak Messenger Service. "There's nothing but tar and smoke on your face." Ruiz, a star on the Travel Channel's bike messenger show "Triple Rush," said he once had to miss a day of work to see a doctor because of exhaust burning his eyes.
Pedaling behind pollutant-spewing cars and trucks may not seem as scary as being hit by one, but scientists say it can pose invisible dangers.
Now, 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.
Pedaling behind pollutant-spewing cars and trucks may not seem as scary as being hit by one, but scientists say it can pose invisible dangers."Our findings suggest that short-term exposure to traffic may have a significant impact on cardiac autonomic function in healthy adults," the scientists from Health Canada, Environment Canada and the University of Ottawa wrote in the journal Environmental Health Perspectives.
The study does not suggest that bikers would be better off driving, experts say. Rather, the findings intensify the scrutiny on cyclists' pollution exposure, and point to simple solutions for a cleaner ride, such as avoiding busy roads like 8th Avenue whenever possible.
"It's something that actually concerns a lot of people that do cycle," said Michael Brauer, a cyclist and atmospheric scientist at the University of British Columbia who was not involved in the new study. "People want to understand their risk. They're just thinking all the time, 'Is this good for me? Is this bad for me? I'm doing my part, but there's this car that's throwing this exhaust in my face.' "
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 heavy traffic 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," said Arden Pope, an expert in the health effects of air pollution and professor at Brigham Young University in Provo, Utah. "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."
But 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.
Researchers are not sure how air pollution alters heart rate variability. One idea is that particles in the lungs cause inflammation, which throws off the body's ability to carry out its automatic functions.For the Canadian cyclists, when their exposure to certain pollutants, including ultrafine particles, nitrogen dioxide or ozone, increased, their heart rate variability decreased, according to the study.
Sheer proximity to tailpipes is one reason why cyclists have a high exposure to the tiny particle pollutants, which are emitted by vehicles along with thousands of other chemicals. Diesel buses and trucks are among the worst offenders.
"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 – something that's missing for most of 8th Avenue – is important for cyclists.
Two white stripes of paint, with a few feet of cycling space between them, is all that is reserved for bikers on this crowded street. Trucks commonly idle on the bike lane. Heavy traffic creates a wind tunnel that traps pollution on the road, according to a study by the California Air Resources Board.
A 2010 study of cyclists in the Netherlands showed that hard-pedaling, deep-breathing cyclists on busy roads inhale more of this dirty air. In many cases, they also spend more time exposed to it compared to someone driving the same distance.
"Those things add up and they give cyclists that cycle in traffic a high exposure," Brauer said.
But whether that exposure ups a cyclist's risk for heart or breathing problems has been less well established. One small study of Netherlands cyclists found a weak link between exposure to ultrafine particles and soot and airway inflammation.
The new study of Canadian cyclists does not mean that people should lock up their bikes and hop back into the driver's seat, said Brauer. Another study has shown that drivers have higher respiratory problems than cyclists because of their higher exposure to volatile organic chemicals in vehicle exhaust.
"In stop-and-go traffic, [drivers] have more exposure than a cyclist who stays 15 feet or more from the tailpipes," said Rebecca Serna, executive director of the Atlanta Bicycle Coalition, a cycling advocacy group.
The health benefits of cycling far outweigh the risks from air pollution and traffic collisions relative to car driving, according to one estimate by researchers in the Netherlands, where cycling is king. Taking cars off the road also helps reduce greenhouse gas emissions and traffic accidents.
"In general, you're better off cycling than not," Brauer said. "The physical activity benefits outweigh negative impacts. But you'd like there to be no impacts."
Exposure to dirty air adds to the perception problem that cycling is unsafe, said C.H. Christine Bae, an urban planner at the University of Washington in Seattle, who specializes in how bike facilities affect air pollution exposure.
The Canadian study authors have a simple solution. Avoid busy streets.
"In general, you're better off cycling than not. The physical activity benefits outweigh negative impacts. But you'd like there to be no impacts." – Michael Brauer, cyclist and atmospheric scientist, University of British Columbia"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.
"Our recommendations to cyclists would be to avoid busy as streets as much as possible," said Dimitri Stanich, a spokesman for California's Air Resources Board.
Of course, cyclists might want to avoid busy streets for a number of reasons – fewer distracted drivers being one. But the busiest streets also have the dirtiest air, with ultrafine particle and soot exposure highest on busy roads, according to a recent study.
Bike routes should aim to minimize time spent on these high-traffic roads, the Canadian researchers wrote. This would reduce exposures of riders who may be more susceptible to the immediate health risks of traffic-related air pollution, such as the elderly, children, and pregnant mothers.
A study of bike lanes in Portland, Ore., showed that lanes separated by planters, not just by white paint, actually decreased cyclists' air pollution exposure. A Belgian study of traffic pollution found that cycling as little as several feet off the road gave measurable differences in exposure.
"Little things like that can help a lot to reduce exposure to cyclists," Bae said.
If a little is good, more is better. Brauer says the preliminary results of his lab's work suggest that bike lanes are best when built one block from a major traffic artery. Despite the emerging research, Bae said that she does not know of any cities that consider cyclists' pollution exposure when designing bike lanes.
Including Vancouver, where Brauer cycles, many of the cities that built bike lanes one block away from a major road thought about cost, not pollution.
"Most were done by accident, because they were cheaper," Brauer said. "But they actually give you an air pollution benefit."