Air pollution is propelling an exponential rise in dementia cases around the world, a global study has suggested.
Cases of the disease are increasing at a rate of more than 20 per cent a year, most of which are in developed countries where air pollution is rife.
Scientists found people were more likely to develop dementia later in life when they were exposed to two air pollutants over a long period of time.
The researchers at the University of New South Wales are particularly concerned by nitrogen dioxide and sooty smog pumped out by old diesel cars.
The microscopic particles in air pollution are breathed deep into the lungs and enter the blood stream.
Scientists believe they then travel into the brain where they provoke inflammation and increase the risk of strokes– problems which may trigger dementia.
The findings, published in the Journal of Alzheimer's Disease today, provide further evidence that toxic fumes are linked to Alzheimer's and other forms of dementia.
Some 850,000 people in the UK 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 caused by genetics, with smoking, obesity and lack of exercise increasing the risk.
But the study suggests air pollution also plays a major role. More than 40,000 people in the UK are thought to die early every year because of air pollution.
The lead author of the new study, Dr Ruth Peters, said it's difficult for people to reduce exposure if they live where pollution levels are high.
‘This study finds mounting evidence that air pollution increases the risk of developing dementia later in life.
‘However, unlike the majority of established dementia risk factors, it is very difficult for someone to reduce their exposure to air pollution, especially if they live somewhere where pollution levels are high.
'This is concerning because the World Health Organisation (WHO) estimates 91 per cent of the world's population lives in places where air quality exceeds WHO guideline limits.
‘This research shows that government regulation that reduces our exposure to air pollution has a huge potential health and economic benefit.’
But Hilda Hayo, CEO of Dementia UK, said city dwellers were not to worry too much about the recent findings.
She said: 'The causes of dementia are complex and not fully understood, so it’s important that people who live in cities do not worry unduly about the link between air pollution and dementia.
'People are living for longer which is also contributing to rise in dementia diagnosis rates.
'Nevertheless, everything that is good for your heart is also good for your brain, so we suggest people make healthy choices, including eating a balanced diet and exercising regularly – away from main roads wherever possible.'
The research team reviewed 40 studies on dementia risks in Canada, Sweden, Taiwan, Britain and the US, involving around 1,500 participants.
It is not the first study to link pollution to dementia, with researchers from King's College and St George's, University of London finding last year that people living in areas polluted by traffic and industry are 40 per cent more likely to develop dementia. They calculated that air pollution could be responsible for 60,000 cases of dementia in the UK.
The UK is notoriously bad at controlling air pollution, with 37 cities persistently displaying illegal levels and the Government repeatedly being hauled into court over the past few years.
Diesel cars have been promoted since the 1970s as an environmentally-friendly choice because they emit less carbon dioxide. Tony Blair's Labour government, in particular, used generous tax breaks to persuade drivers to buy diesel cars.
The tactic contributed to the number of diesel drivers jumping from 1.5million a decade ago to about 11million today.
But in recent years scientists have realised that diesel also produces more of the tiny particles and nitrogen oxides that are damaging to our health.
Nearly 70,000 lives were lost to the illness last year – 13 per cent up on the 61,000 of 2015.
Experts warn the figure will keep increasing because people are living longer and conditions such as Alzheimer’s are still untreatable.
The Office for National Statistics said the illness was responsible for 12.8 per cent of the 541,589 registered deaths in England and Wales last year. It has been the nation’s biggest killer since 2016.
In the two years since the Government promised to publish a social care plan, families have been forced to find £15billion to support relatives with the illness.
Middle-class families are among the hardest hit because free care is given only to those with less than £23,250 in savings or housing wealth.
Matt Birnholz, MDPeer