Air pollution has long been linked to health conditions such as stroke, heart disease and lung cancer. According to a new Canadian study, polluted air may also boost the risk of breast cancer.

tracked nearly 90,000 Canadian women over two decades and found that younger women who live in areas that experience high air pollution had a staggering 30 per cent higher risk of developing breast cancer before menopause than others.

Carleton University health sciences researcher Dr. Paul Villeneuve, an author of the study, said it is “building the evidence that air pollution is indeed linked to the development of cancer.”

Emily Piercell was just 27 years old when she found a lump in her breast.

“I was shocked and scared,” she told CTV News. “I don’t have any cancer, breast cancer in my family. I’m so young.”

The study offers Piercell a possible clue. She grew up in Windsor, Ont., which experiences persistently high levels of fine particle air pollution.

“Pollution is awful for our bodies,” Piercell said. “So to see that link, it’s not surprising to me.”

She is now eating right and has taken up half marathons, doing what she can to stay healthy after undergoing a double mastectomy, radiation and chemotherapy.

Researchers suspect that tiny particles in polluted air may promote inflammation or make breasts denser and thus more prone to developing tumours. The believe that the link between pollution and breast cancer is pronounced among women before menopause because their hormones are more active then and may interact more with chemicals in the environment.

Scientists say that the best prevention would be a worldwide reduction in air pollution. Until that happens, Dr. Anthony Miller of the University of Toronto’s Dalla Lana School of Public Health says there are several things young women can do to lessen their exposure.

“If you’re living in an area where there is a great deal of air pollution, you should do your best to remove it from your environment,” Miller, who co-authored the study, told CTV News. “Keep your windows closed, have good air conditioning with good filters. At the moment, that’s all we can advise people to do.”

According to the , around seven million people die every year from being exposed to fine particles in polluted air.

The study is published in the journal Environmental Epidemiology.

With files from CTV’s medical affairs specialist Avis Favaro and producer Elizabeth St. Philip