'Safe' levels of pollution could cause Parkinson's or Alzheimer's: Poor air quality may be linked to dementia, new study suggests

 Living in a polluted area significantly raises the risk of dementia, according to the world's largest study on the issue.

Scientists found that the higher the level of toxic air in a postcode, the more likely its residents are to be hospitalised with Alzheimer's or Parkinson's disease.

The research showed that any air pollution – even within 'safe' limits – is linked to neurological diseases.

The study by Harvard University, published yesterday in the Lancet Planetary Health journal, drew on data from 63 million adults. 

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Pollution can significantly raise the risk of dementia, a new study has found (stock image)

It is the strongest evidence that dirty urban air can damage the brain.

Air pollution is already known to cause lung disease, asthma and heart disease, cutting short around 40,000 lives a year in the UK.

The study analysed the link between progressive neurological conditions and tiny pollution particles known as PM2.5, which form as a result of burning diesel, petrol, wood and coal. 

The World Health Organisation (WHO) states that the amount of PM2.5 pollution must not exceed annual average levels of 10 micrograms of toxic particle per cubic metre of air.

Experts compared the health records of 63 million over-65s in America with air pollution data for the- ir postcode.

The participants were followed over 17 years, during which time one million developed Parkinson's disease and 3.4 million dementia.

For every five microgram rise in air pollution, the likelihood of getting admitted to hospital with either Alzheimer's or Parkinson's increased by 13 per cent. 

Women were slightly more vulnerable than men.

The study found that this increased risk existed even when air pollution was relatively low, showing there is 'no safe threshold for harmful pollution'.

It concluded: 'Long-term exposure to air pollution is significantly associated with a higher risk of neurological health deterioration, even at concentrations less than the current national standards.' 

Fiona Carragher, director of research and influencing at Alzheimer's Society

In the UK as a whole the average level of PM2.5 in urban areas is 10. And average levels are above 15 in some busy areas of cities.

The microscopic pollution particles are less than 1/30th the width of a human hair, and are able to penetrate the lungs and enter the bloodstream.

The authors said they may cross the blood-brain barrier, increasing inflammation in the brain and causing conditions including dementia.

Two years ago researchers at King's College London calculated that air pollution could account for 60,000 of the UK's 850,000 dementia cases. 

Fiona Carragher, director of research and influencing at Alzheimer's Society, said: 'Air pollution is a hot topic in dementia research. 

'While this study adds to the evidence that air pollution could raise your dementia risk, we still need to know how particulate pollution might be causing changes in the brain, and if these lead to dementias. 

'This study only looked at people with dementia admitted to hospital and we can't rule out the possibility of other factors.'

Around 145,000 people in the UK live with Parkinson's, which is a progressive neurological condition.

Dr Beckie Port, research manager at Parkinson's UK, said: 'This research provides the most robust evidence to date that long-term exposure to air pollutants may play a role in the deterioration of incurable conditions. 

'There is increasing evidence that air pollution is linked with both the occurrence and progression of such conditions.'

Mike Childs, of Friends of the Earth, said: 'Cities and towns across the UK fail the WHO standard for particle matter – the most dangerous type of air pollution.

This study is proof that the Environment Bill must lock WHO standards into law. The Government must also end its fixation with road building.'

Andrea Lee, from the environmental law charity ClientEarth, said: 'We have long known that there is no safe level of air pollution and this study shows tragic health impacts can occur even when fine particulate matter pollution is within the limits currently set in UK law.'