Researchers at Montreal's Research Institute of McGill University Health Centre, McGill University and Universite de Montreal found a link between post-menopausal breast cancer and exposure to nitrogen dioxide -- a "marker" for traffic-related air pollution.
The study, published in Environmental Health Perspectives, found the risk of breast cancer increased by about 25 percent with every increase of nitrogen dioxide of 5 parts per billion.
"Another way of saying this is that 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," study co-author Dr. Mark Goldberg of the Research Institute said in a statement.
Goldberg and colleagues had created two air pollution "maps" showing levels of nitrogen dioxide -- a by-product of vehicular traffic -- in different parts of Montreal in 1996 and 10 years earlier in 1986. They then charted the home addresses of women diagnosed with breast cancer in a 1996-97 study onto the air pollution maps.
The incidence of breast cancer was clearly higher in areas with higher levels of air pollution, the study said.