Pollution Trips Up Female Marathon Runners

Female marathon runners take heed: If you want to run your best race, you'd be advised to look at the pollution levels before you choose your course.

Higher levels of coarse particle pollution appear to slow marathon times for women, according to research presented today by Linsey Marr of Virginia Tech.

Marr and colleague Matthew Ely of the U.S. Army Research Institute of Environmental Medicine considered marathon times in seven cities -- Boston, New York, Chicago, Minneapolis/St. Paul, Sacramento, Los Angeles and Duluth, Minn. -- over the years 1980 to 2007.

They calculated how much slower the average of the top three finishers' times was compared to the course record. The researchers then weighed those times with levels of various pollutants on the day of the marathon.

The team accounted for variations in temperature, sunshine and humidity, which all have a strong effect on performance. The optimum temperature for marathon running is 54 degrees Fahrenheit, according to researchers' findings.

The pair found no significant relationship between marathon times and the levels of carbon monoxide, ozone, nitrogen dioxide or sulfur dioxide.

This was a partial surprise. "I was expecting to see a relationship, if any, between carbon monoxide -- because carbon monoxide displaces oxygen in your blood -- or potentially ozone, because we know ozone causes respiratory irritation," Marr told the audience at the American Association for Aerosol Research annual meeting in Minneapolis.

Marr noted that ozone levels tend to be low on weekend mornings, when marathons typically are run, so runners probably do not experience high enough levels to cause a problem.

There was one set of pollutants -- coarse particles smaller than 10 microns in diameter -- that did have an effect on running times, but only for women. Fine particles less than 2.5 microns in diameter did not have an effect.

"This was a surprise to me," Marr said, because many studies have shown more negative health effects from fine particles than from coarse particles. "But in fact what we found is that there was a significant relationship."

Every 10 micrograms per cubic meter increase in coarse particles corresponded to a 1.4 percent increase in marathon time for women, the team found, equivalent to more than a minute extra on the women's marathon world record time.

Typical coarse particle concentrations in U.S. cities average between 20 and 40 micrograms per cubic meter.

The reason women are affected but not men are not, the researchers believe, is that women's tracheas, or windpipes, are 32 percent smaller on average. Particles are much more likely to hit the sides of the smaller tracheas and stick.

This means that a larger percentage of the particles women inhale deposit in their throats, where they presumably cause irritation.

"There is evidence in the literature to suggest that discomfort in this area can affect athletic performance," Marr said.

The findings were food for thought for aerosol scientist and marathon runner Annemarie Carlton of the U.S. Environmental Protection Agency in Research Triangle Park, N.C.

"You might pick a marathon based on where it is or what the temperature might be," she said, "but you might also think about what the pollution might be like, especially if you are trying to qualify for Boston."

Alternatively, she suggested: "I need to get a bigger trachea. That's one way around it."