People who live near high-traffic roadways may face a higher risk of developing dementia than those who live farther away, warns a new study which suggests that air pollution from vehicles may be a factor in the development of the neurological disorder.

Researchers, including those from Institute for Clinical Evaluative Sciences (ICES) in Canada, found that people who lived within 50 metres of high-traffic roads had a seven per cent higher likelihood of developing dementia compared to those who lived more than 300 meters away from busy roads.

They examined records of more than 6.5 million Ontario residents aged 20-85 to investigate the correlation between living close to major roads and dementia, Parkinson's disease and multiple sclerosis.

Scientists 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.

In addition, they mapped individuals' proximity to major roadways using the postal code of their residence.

The findings, published in the The Lancet journal, indicate that living close to major roads increased the risk of developing dementia, but not Parkinson's disease or multiple sclerosis, two other major neurological disorders.

"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," said Hong Chen, scientist at Public Health Ontario (PHO).

"With our widespread exposure to traffic and the greater tendency for people to live in cities these days, this has serious public health implications," said Chen.

The study also found that the increase in the risk of developing dementia went down to four per cent if people lived 50-100 metres from major traffic, and to two per cent if they lived within 101-200 metres.

At over 200 metres, there was no elevated risk of dementia.

"Our study is the first in Canada to suggest that pollutants from heavy, day-to-day traffic are linked to dementia," said Ray Copes from PHO.

"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," said Copes.

"This study suggests air pollutants that can get into the brain via the blood stream can lead to neurological problems," Copes added.

As urban centres become more densely populated and more congested with vehicles on major roads, Copes suggests the findings of this paper could be used to help inform municipal land use decisions as well as building design to take into account air pollution factors and the impact on residents.