Living near traffic pollution tied to heart deaths

NEW YORK (Reuters Health) - Middle-aged and older adults who live near high-traffic roads may have a heightened risk of dying from heart disease -- but the odds seem to go down if they move to a less-traveled neighborhood, a new study finds.

The findings do not prove that traffic pollution is the reason for the excess heart disease deaths, researchers say. But they do add to evidence tying vehicle-produced pollutants to the risk of dying from heart problems.

In May, the American Heart Association (AHA) released a report stating that recent studies have “substantially strengthened” the evidence that air pollution from traffic, industry and power generation is a risk factor for heart attack, stroke and deaths from cardiovascular causes.

The evidence most strongly points to particles known as fine particulate matter, which is produced from burning gasoline and other fossil fuels.

The AHA recommends that people with established heart disease and other at-risk individuals -- including the elderly and people with risk factors for heart disease, like diabetes and high blood pressure -- try to limit their exposure to congested roadways and spend less time outside on days when air quality is poorer.

For this latest study, Wen Qi Gan and colleagues at the University of British Columbia in Vancouver, Canada, analyzed data on more than 450,000 Vancouver-area residents between the ages of 45 and 85.

They found that over nine years, residents who consistently lived within roughly 500 feet of a highway or within 165 feet of a major road were more likely to die of heart disease than those who lived farther from high-traffic roadways.

But the researchers also found “two new twists” to what’s been known about the relationship between traffic and heart disease deaths, explained senior researcher Dr. Michael Brauer, a professor of environmental health at the university.

That is, the risk of heart disease death declined among residents who moved away from high-traffic roads during the study period, while it increased among those who moved closer to congested roads.

“It’s sort of like what we see with smoking cessation,” Brauer said in an interview. “The associated disease risks are lower in former smokers,” compared with persistent smokers.

The findings are based on 450,283 middle-aged and older adults with no known heart disease at the outset. Nearly 53,000 persistently lived within 500 feet of a highway or 165 feet of a major road over the nine-year study.

Of those residents, 607 -- or just over 1 percent -- died of heart disease during that period; that compared with 0.7 percent of the more than 328,000 people who persistently lived farther from traffic.

The researchers were able to account for a number of other factors that could explain any connection between living near major roads and having a higher risk of dying from heart disease -- including residents’ age, neighborhood income levels and any diagnoses of diabetes or major lung disease.

They found that living near a highway or major road was still linked to a 29 percent higher risk of heart disease death, versus living farther away. Among people who either moved away from or closer to a major road, the risk of heart disease death was also somewhat elevated -- but lower when compared with residents who persistently lived near busy roads.

In addition, the researchers used air pollution data to show that people living close to highways and major roads would have been exposed to higher levels of particulate matter, nitrogen dioxide and other traffic-related pollutants.

The findings do not prove that air pollution was the reason for the higher risks. Brauer said that traffic noise, for example, might be involved. In addition, the researchers had no information on certain key factors in heart disease risk, including people’s smoking habits and weight.

However, a body of research has now linked air pollution exposure to the risk of heart disease death, Brauer pointed out. And, he said, the evidence suggests that traffic pollution may be a particular risk.

A “big question,” Brauer said, is whether exposure to air pollution is linked to the initial development of heart disease -- or whether its association with heart disease death reflects an effect mainly on people with existing heart problems.

Researchers believe that air pollutants may trigger heart attacks, strokes or other cardiovascular “events” in vulnerable people by causing inflammation in the blood vessels and irritating the nerves of the lungs.

Brauer suggested that people view traffic pollution as one of the range of factors that may influence their heart disease risk -- which includes exercise and diet habits, smoking and the presence of any health conditions that contribute to heart disease, like diabetes, high blood pressure and high cholesterol.

Living near major roads does not mean a person is destined for heart disease. And, Brauer noted, living in a low-traffic area does not mean a person can slack on following a healthy lifestyle.

SOURCE: Epidemiology, online June 25, 2010.