Does living near a freeway increase your risk of dementia?

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Health researchers have long known that living near freeways increases the risk of cancer, heart disease and asthma. But a new study by two Canadian research institutes says that it also increases the risk of developing dementia. 

Noting recent studies that suggest living near major roads might damage cognition, researchers at Public Health Ontario and the Institute for Clinical Evaluative Sciences set out to investigate whether there's a correlation between such proximity and three neurological diseases: dementia, Parkinson's disease and multiple sclerosis.

The study examined the 2001-2012 health records of about 6.6 million Ontario residents aged 20-85, and found a correlation with dementia. It reported that the degree of risk increased the closer one lived to a freeway: People who lived within approximately 600 feet faced a 2 percent higher risk of developing dementia, whereas people who lived within approximately 150 feet had a 7 percent increased risk.

The study, published in The Lancet, found no increased risk for Parkinson's or multiple sclerosis. 

The researchers did not try to determine why there was an increased risk of dementia.

"The significance of these findings is mostly from a public health rather than an individual health perspective," said Dr. Ray Copes, a University of Toronto professor and study co-author. "Measures that would achieve further reductions in emissions from traffic is one thing that could be done to help."

Better city planning and building design could help reduce exposure to pollutants for people living near freeways, he said. 

"There’s no doubt that exposure to environmental risks affects mental health," said Dr. Roderick Shaner, medical director for the Los Angeles County Department of Mental Health. "We have to be cognizant in our land use planning."