After taking risk factors such as hereditary into account, researchers found the number of breast cancer cases was far higher in areas with high levels of traffic generated pollution.
The researchers used maps measuring pollution from vehicles in 130 spots around Montreal, Canada. They used the home addresses of post menopausal women already diagnosd with breast cancer.
They found that women living in the areas with the highest levels of pollution were twice as likely to develop the disease.
According to the Globe & Mail air pollution was also a problem if there was a school nearby and parents left their cars running when dropping off their childrten. The pollution rose on those neighbourhood streets.