Chronic exposure to traffic-related air pollution can make cells in the body look older — about 10 years older, a new study finds.

Andrea Baccarelli of the University of Milan, Italy, and his colleagues extracted genetic material from white blood cells that had been collected from 57 office workers and 77 people who spent their days in the road directing traffic. They focused on telomeres, repetitive segments of DNA that serve as protective caps on the tips of chromosomes.

As a general rule, as cells divide, the length of that protective telomere in each successive generation shrinks. Eventually, the telomeres on some daughter cells become so short that a chromosome begins to degrade, which puts a halt to future cell division. So telomere length can serve as a rough gauge of biological aging, Baccarelli says. And in his team’s new study, although telomeres were shorter for older workers in each employment category, telomers were disproportionately short in the traffic officers.

After accounting for age, telomere shortening was roughly 15 percent greater in traffic officers than in the office workers, the researchers reported this week in San Diego at the American Thoracic Society annual meeting.

The researchers then restricted their analysis to telomere length in the traffic officers. Each participant had been fitted with an air-sampling monitor to wear throughout a work day. It measured benzene, a gaseous constituent of auto exhaust. In this study, benzene readings served as a proxy for an individual’s exposure to the mix of pollutants associated with traffic.

All of the traffic officers had been assigned street duty for at least five years. The average telomere length in those who worked in low-traffic areas (32 people) was about the same as those measured in the office workers. However, telomere length in the workers assigned to highly trafficked streets (45) was substantially shorter — equivalent to the shortening associated with about 10 years of age in normal healthy people.

So based on telomere length, Baccarelli says, the blood of workers who regularly had high daily exposures to combustion exhaust “looked 10 years older” than it should.

There’s some debate about what such findings might mean, since blood assays do not measure effects from cells throughout the body. But the trend is worrisome, Baccarelli says, since a number of studies over the past decade have linked shorter telomeres with elevated risk of chronic ails, such as cardiovascular disease and cancer.

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