A new Canadian study finds that living near major roads is associated with an increased risk of developing dementia.
Funded by Health Canada and undertaken by researchers at Public Health Ontario and the Institute for Clinical Evaluative Sciences, the study looked at health records for 6.5 million people aged 20 to 85 living in Ontario over an 11 year period and tracked potential correlations between proximity to major roads and either multiple sclerosis, Parkinson’s disease or dementia. While no connection was found in the cases of MS and Parkinson’s, the team did uncover a statistically significant link for dementia.
Compared with those Ontario residents living at least 300 metres from a major road, those living within 50 m had a seven per cent higher risk of developing dementia, those between 50 and 100 m had a four per cent higher risk and those between 100 and 200 m had a two per cent higher risk. Overall, the study suggested that a full seven to 11 per cent of dementia cases attributed to people living within the 50 m zone could be caused by the vehicle traffic.
“Increasing population growth and urbanisation have placed many people close to heavy traffic,” says Dr. Hong Chen, study co-author from Public Health Ontario in Toronto, to BBC News. “And with widespread exposure to traffic and growing rates of dementia, even a modest effect from near-road exposure could pose a large public health burden.”
The study did not speak to the potential source of the correlation but experts suggest a range of factors from noise pollution to particles released from tire wear to, most prominently, vehicle emissions: nitrogen oxides, carbon monoxide and unburned hydrocarbonds are all potential culprits.
Car exhaust is a well-known contributor to higher rates of asthma, bronchitis and cardiac disease in urban centres, but the link between air pollution and neurological disease is less established. One 2015 study found a link between increased long-term exposure to fine particulate (air particles less than 2.5 micrometres in size, composed of dust, dirt, soot and smoke) and both a reduction in total brain volume and a increased risk of covert brain infarcts, so-called “silent” strokes.
The World Health Organization states that seven million people died worldwide in 2012 due to air pollution and that about 40 per cent of these cases were linked to stroke.
About 564,000 Canadians are currently living with dementia, according to the Alzheimer Society of Canada, with about 25,000 new cases being diagnosed every year. Stated risk factors for developing dementia include genetics, aging, diabetes, smoking, unhealthy diet and physical inactivity.
“Little is known in current research about how to reduce the risk of dementia,” said lead author of the new study, Dr. Hong Chen, environmental and occupational health scientist at Public Health Ontario, to the Toronto Star. “Our findings show the closer you live to roads with heavy day-to-day traffic, the greater the risk of developing dementia.”
The study reports that 19 per cent of Ontarians live within 50 m of major roads and that almost half the population lives within 200 m.