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Toront's Allen Road in heavy congestion. (Dave Chan for The Globe and Mail)
Toront's Allen Road in heavy congestion. (Dave Chan for The Globe and Mail)

Breast cancer linked to traffic-related air pollution Add to ...

Women living in areas with high levels of traffic-generated air pollution may be at greater risk for breast cancer, Montreal researchers have found.

Scientists from McGill University and the University of Montreal say that while their findings are "disturbing," they insist the subject needs more investigation.

"This is really a dramatic association," said study co-author Mark Goldberg, a McGill environmental policy professor. "We never thought that breast cancer would be related to air pollution. We were shocked."

The researchers used maps measuring pollution from cars and other vehicles at 130 spots around Montreal; then they crossed the information with the home addresses of postmenopausal women diagnosed with breast cancer.

The results, published in the journal Environmental Health Perspectives, were "startling," the researchers said. Even after taking risk factors such as family history into account, they found that the incidence of breast cancer was markedly higher in more polluted zones.

"Women living in the areas with the highest levels of pollution were almost twice as likely to develop breast cancer as those living in the least polluted areas," said Prof. Goldberg, a researcher with the McGill University Health Centre.

The researchers examined exposure to smog-causing nitrogen dioxide, and found the risk for breast cancer rose about 25 per cent with every increase of nitrogen dioxide of five parts per billion.

Air pollution wasn't only a problem for people living next to busy downtown streets or expressways. It also rose on neighbourhood streets if there was a school nearby and parents left their cars idling while dropping off their children.

"These are small pockets of air pollution," said co-author France Labrèche, an epidemiologist at the University of Montreal.

The findings add to the weight of evidence linking air pollution to a range of health problems. Research has already established a connection to lung cancer and cardiovascular disease.

But the researchers cautioned that their study does not conclude that nitrogen dioxide causes breast cancer, and more study is needed. "One study is not enough to be able to assert that there is a causal relationship," Prof. Labrèche said.

Also, the authors did not factor in the amount of time women spent indoors or outdoors, or how much time they spent at home.

Still, it should prompt decision-makers to try to reduce urban air-pollution through measures like improving public transit or even synchronizing traffic lights to reduce idling, the researchers said.

The authors crossed over results from air-pollution measurements in 2005 and 2006; they then extrapolated the data to find calculations for the mid-90s, the years they tracked home addresses for women with breast cancer.

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