People living in urban areas near high traffic roads are at higher risk of developing dementia, according to a study published last week in the medical journal The Lancet.

The effects of air pollution (causing 6.5 million deaths every year) and traffic noise on the human body, including on the brain, have been subject of research for the past years. But so far, little was known about its relationship with the incidence of dementia, Parkinson’s disease, and multiple sclerosis.

Now, a study led by scientists at Public Health Ontario in Canada, has found that up to one in 10 cases of dementia among those living 50 metres from a busy road could be related to exposure to high levels of traffic.

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The authors tracked all adults between the ages of 20 and 85 living in Ontario — around 6.6 million people — from 2001 to 2012. Then they used postal-code addresses to determine the person’s proximity to major roadways and analysed medical records to see who went on to develop these neurological diseases.

Over the course of the study, approximately 243,600 people were diagnosed with dementia, 31,600 with Parkinson’s disease, and 9250 with multiple sclerosis. Despite the number of cases identified, the scientists found no association between living close to heavy traffic and Parkinson’s disease or multiple sclerosis.

They found, however, that dementia was more recurrent among those living closer to main roads. People living within 50 metres of a busy road were 7 to 12 per cent more likely to develop dementia, depending on how long they lived there and if they lived in an urban or rural area. The risk dropped down to 4 per cent for residents at 50-100 metres and 2 per cent at 101- 200 metres. For those living more than 200 metres away, the risk dissipated.

People living within 50 metres of a busy road are 7 to 12 per cent more likely to develop dementia.

“The challenge is to look at different ways of laying out of communities so that we have a higher percentage of our population who are located or residing more than 200 meters away from major traffic arteries,” said Ray Copes, the director of environmental and occupational health at Public Health Ontario and co-author of the Lancet paper.

Better building designing and planning cities with more dispersed traffic are among the measures that could help reduce exposure to pollutants, according to Copes.