It seems that neuroscientists are just now discovering what real estate agents have known all along: living near a highway can be hell.

New research from Public Health Ontario and the Institute for Clinical Evaluative Sciences indicates that people who live close to high-traffic roadways face a higher risk of developing dementia than those who live further away.

...and it's no small discrepancy: If you live within 50 meters of high-traffic roads you have a 7 percent higher likelihood of developing dementia compared to people who live more than 300 meters away from busy roads. The increase in the risk of developing dementia went down to 4 percent if people lived 50 to 100 meters from major traffic, and to 2 percent if they lived within 101 to 200 meters. At over 200 meters, there was no elevated risk of dementia. There was no correlation between major traffic proximity and Parkinson's disease or multiple sclerosis.

"Little is known in current research about how to reduce the risk of dementia. Our findings show the closer you live to roads with heavy day-to-day traffic, the greater the risk of developing dementia. With our widespread exposure to traffic and the greater tendency for people to live in cities these days, this has serious public health implications," says Dr. Hong Chen, environmental and occupational health scientist at PHO and an adjunct scientist at ICES.

The study mapped individuals' proximity to major roadways using the postal code of their residence. The researchers identified 243,611 cases of dementia, 31,577 cases of Parkinson's disease, and 9,247 cases of multiple sclerosis in Ontario between 2001 and 2012.

"Our study is the first in Canada to suggest that pollutants from heavy, day-to-day traffic are linked to dementia. We know from previous research that air pollutants can get into the blood stream and lead to inflammation, which is linked with cardiovascular disease and possibly other conditions such as diabetes. This study suggests air pollutants that can get into the brain via the blood stream can lead to neurological problems," says Dr. Ray Copes, chief of environmental and occupational health at PHO and an author on the paper.

The researchers believe that, as cities become more densely populated and more congested with vehicles on major roads, their work can be used to help guide urban planners and architects to take into account air pollution factors and the impact on residents.

The research was published in The Lancet.