Live on a busy road? Then you're SIGNIFICANTLY more likely to develop dementia, shock study finds

Millions of people have a significantly greater risk of developing dementia because they live near a busy road, a major study suggests.

Scientists found people exposed to traffic fumes and noise were up to 12 per cent more likely to develop the disease.

And among those at the highest risk – those living within 50 metres of a major road – up to one in nine cases of dementia might be caused by traffic exposure.

The study, which tracked nearly seven million people for more than decade, is the largest study to suggest environmental factors could play a major role in dementia risk.

An estimated 850,000 people in the UK currently have dementia, and the number is expected to soar to one million by 2025 and two million by 2050.

The disease is thought to be largely linked to genetics – but increasing evidence suggests other factors such as smoking, obesity and lack of exercise may increase the risk.

The new study, published last night in the Lancet medical journal, suggests air pollution and noise may also play a role.

The Canadian research reveals the closer someone lives to a major road – and the longer they live there – the higher their risk of developing dementia.

Study leader Dr Hong Chen, of the University of Toronto and Public Health Ontario, 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.’

The team plotted the addresses of 6.6million adults aged between 20 and 85 living in the Canadian province of Ontario, and then tracked them for 11 years between 2001 and 2012.

The team found those living within 50m of a major road – defined as a main urban road or a motorway – were 7 per cent more likely to develop dementia than those who lived 300m away.

Those who lived between 50 and 100 metres away had a 4 per cent increased risk, and those between 101 and 200 metres a 2 per cent increased risk.

They also found that people lived within 50m of a major road in towns and cities, and those who lived within 50m of a major road for the entire study period, had the highest risk – of 12 per cent greater than those who lived more than 300m away.

Those living more than 200m from a major road had no increased dementia risk, the scientists found, and no link was found between proximity to busy roads and Parkinson’s disease or multiple sclerosis.

Among the Ontario population, half live within 200m of a major road and more than one in five live within 50m of a major road, the researchers calculated.

In Britain – which has a population density five to times that of Ontario – many more people live near main roads, including the vast majority of people living in cities.

The UK is also notoriously bad at controlling air pollution, with 37 cities across Britain persistently breaching legal limits of air toxins set by the EU.

The new findings add to evidence that long-term exposure to air pollution and traffic noise may contribute to brain shrinkage and mental impairment.

Scientists think this is because nitrogen dioxide and the sooty particles generated by diesel engines interfere with the blood-brain, the crucial membrane which stops harmful chemicals entering brain cells.

They also think pollution may provoke inflammation in the brain, a problem which may trigger dementia.

Other studies have found that persistent noise is linked to cognitive impairment, which may also explain the findings.

Medical experts are increasingly aware of the impact of traffic on human health, including the risk of asthma and heart disease, but this is the first time such a strong link has been made between traffic exposure and dementia.

NHS watchdog NICE last month warned air pollution now contributes towards 25,000 deaths a year in England – almost 5 per cent of all deaths.

It called for a reduction in speed limits and traffic to be restricted around schools.

British experts described the findings as ‘important’ and ‘provocative’, but stressed that they highlighted associations and did not demonstrate a causal link between exposure to traffic and dementia.

Dr David Reynolds, chief scientific officer at Alzheimer’s Research UK, said: ‘This study has identified major roads and air pollutants from traffic as possible risk factors for dementia, a finding which will need further investigation before any firm conclusions can be drawn about the relative risks of air pollutants for dementia versus other risks such as smoking, lack of exercise or being overweight.’

Professor Tom Dening, director of the Centre for Old Age and Dementia at the University of Nottingham, said: ‘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.’

Professor Rob Howard of University College London added: ‘Regardless of the route of causation, this study presents one more important reason why we must clean up the air in our cities.’