Living near a busy road may raise risk of dementia, major study into pollution finds

Living near a busy road may raise risk of dementia, major study into pollution finds

Air pollution and noise could be to blame for thousands of dementia cases each year 

Air pollution and noise could be to blame for thousands of dementia cases each year 

Sarah Knapton, science editor 

4 JANUARY 2017 • 11:30PM

Living near a main road increases the risk of dementia, the first major research into air pollution and disease has shown.

A decade-long study of 6.6 million people, published in The Lancet, found that one in 10 dementia deaths in people living within 50 metres of a busy road was attributable to fumes and noise. There was a linear decline in deaths the further people lived away from heavy traffic.

Air pollution is already known to contribute to the deaths of around 40,000 people in Britain each year by exacerbating respiratory and heart conditions, while previous research showed emissions can cause brain shrinkage.

But the new study by Canadian public health scientists is the first to find a link between living close to heavy traffic and the onset of dementia, a discovery described as "plausible" and "impressive" by British experts.

This study does ask serious questions about the environments where many people live

Prof Tom Dening, University of Nottingham

Dr Hong Chen, the lead author from Public Health Ontario, said: “Our study suggests that busy roads could be a source of environmental stressors that could give rise to the onset of dementia.

“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.

“More research to understand this link is needed, particularly into the effects of different aspects of traffic, such as air pollutants and noise.”

Around 850,000 people suffer from dementia in Britain, and it is now the leading cause of death for both men and women. 

There has been concern that air pollution could be driving neurodegenerative conditions for many years. Last year British scientists discovered tiny magnetic particles produced by car engines and brakes in the brains of people diagnosed with Alzheimer’s disease.

In the new study, the team tracked all adults aged between 20 and 85 living in Ontario for more than a decade from 2001 to 2012.

They used postcodes to determine how close people lived to a main road and analysed medical records to see if they went on to develop dementia, Parkinson’s disease or multiple sclerosis.

Over the study period, more than 243,000 people developed dementia, 31,500 people developed Parkinson’s disease and 9,250 people developed multiple sclerosis.

While there was no association between living near a road and Parkinson’s disease or multiple sclerosis, dementia risk reduced as people lived further from a main road,  with a 7 per cent higher risk in developing dementia among those living within 50 metres; a 4 per cent  higher risk at 50-100 metres and a 2 per cent higher risk at 101-200 metres. After 200 metres there was no increase.

Researchers believe that noise of traffic may also play a role in the raised risk as well as other urban pollution, which is often present near busy roads.

The government is already under pressure to cut pollution after missing EU emissions targets and being ordered by the High Court to come up with a new clean air strategy by the summer.  New guidelines by the National Institute for Health and Care Excellence (Nice) which are out for consultation have suggested that new homes should be built with living rooms at the back to prevent fume exposure.

Experts and environmental campaigners said the Canadian study increased the impetus to improve city air.

“Regardless of the route of causation, this study presents one more important reason why we must clean up the air in our cities,” said Prof Rob Howard, professor of old age psychiatry, at University College London.

Prof Tom Dening, director of the Centre for Old Age and Dementia at the University of Nottingham, added: “It is certainly plausible that air pollution from motor exhaust fumes may contribute to brain pathology that over time may increase the risk of dementia, and this evidence will add to the unease of people who live in areas of high traffic concentration.

“It is unlikely that Ontario has the worst air quality in the world, so the risks might be even greater in cities that are habitually wrapped in smog.

“It is impressive that there seems to be a gradient of risk depending on the distance from the road and  that this is seen for dementia but not two other significant neurological conditions. This study does ask serious questions about the environments where many people live.”

Prof Martin Rossor, NIHR national director for dementia research at University College London Hospitals, said: "The effects are small but with a disorder with a high population prevalence such effects can have important public health implications."

However some scientists were more skeptical, believing that it is impossible to rule out that other social factors are at play. For example people who live near congested roads are likely to be poorer and less well educated than those living in the leafy suburbs, and so prone to worse health.

Prof John Hardy, professor of neuroscience, University College London, said: “The analyses are exceedingly complex with many co-variates included in the model and this always leads to concerns that the analytic complexity is hiding confounding factors in the analytic pipeline.  

“There are several reasons why one might not want to live near a major road, but this study is not an additional one.”

Dr David Reynolds, chief scientific officer at Alzheimer’s Research UK, added: "Studies like this are valuable in revealing new factors that could be implicated in Alzheimer’s disease and other dementias, and opening new avenues for further research.

"Conditions like dementia have multiple risk factors including age and genetics, and other social factors relating to where people live in cities could also be playing a part here. "

http://www.telegraph.co.uk/science/2017/01/04/living-near-busy-road-may-raise-risk-dementia-major-study-pollution

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