People who live near busy roads are at greater risk of developing dementia, according to research published in The Lancet.
Researchers from the University of Toronto found that people exposed to traffic and noise pollution were significantly more likely to develop the disease.
The researchers plotted the proximity of 6.6 million people to major roads. They found that the closer a person lived to a major road — and the longer they lived there — the more likely they were to develop dementia than those living further away.
Those at the greatest risk of dementia (12 per cent) lived within 50 metres of a major road for the entire 11-year duration of the study.
A study last year found toxic nanoparticles called magnetite in ‘abundant’ quantities in human brains. The particles, which come from vehicle engines and open fires, had previously been linked with Alzheimer’s.
The study’s lead author, Dr Hong Chen, said: ‘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.
‘Increasing population growth and urbanisation has placed many people close to heavy traffic, 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.’
This population-based cohort study of over six million residents looked at the relationship between living near a major road and the likelihood of common neurological disorders such as dementia, Parkinson’s disease and multiple sclerosis.
There was no association between proximity to a major road and Parkinson’s disease or multiple sclerosis. This makes sense as, unlike for dementia, the cause of these diseases remains largely unknown.
However, there is already emerging evidence that links dementia to exposure to road pollution and so this research further supports this hypothesis.
The study controlled for important extraneous variables that could confound the results of the study, including diabetes, brain injury, income, access to a neurologist and exposure to selected air pollutants. But it did not account for smoking, lack of exercise and obesity, which can also lead to dementia and must not be ignored.
What such studies can’t tell us is the direction of the relationship, eg, does proximity to major roads cause dementia (likely), does a predisposition to dementia lead to a propensity to choosing property near major roads (unlikely) or does a third factor influence both (possible).
Also, what is it about living close to a major road that leads to the development of dementia — is it more likely that individuals are less active, more sedentary and more likely to drive? Is it high exposure to noxious car fumes containing free radicals, oxides and metals, leading to inflammation and cerebrovascular disease?
Furthermore, despite being a large longitudinal study, it was only based in one region in Canada and thus may not be the same in other areas of Canada or other parts of the world. The Ontario region is more polluted than most regions in Canada and EU and Canadian regulations clearly differ on vehicle emissions, with European vehicles traditionally smaller, driven less (see here and here) and more efficient than their North American counterparts.
This is an important study that may be used to influence policymakers and nudge individuals towards lower car usage. But it will need repeating in Britain if such findings are to be applied here.
Research score: 4/5