Women in their 70s and 80s exposed to high levels of air pollution suffer a greater decline in memory, a study suggests.
Scientists warned they are also at more risk of Alzheimer’s – the most common form of the memory-robbing disease dementia.
Scans of almost 1,000 women from the US showed those regularly exposed to toxic air over the course of three years lost more brain cells.
This process, called brain atrophy, destroys communication in the brain and is seen in patients with Alzheimer’s.
Although there are plenty of studies linking pollution to dementia, this is the first to demonstrate physical changes in the brain with scans.
Women in their 70s and 80s exposed to high levels of air pollution suffer a greater decline in memory and brain cell death, a US study shows
The number of people with dementia is expected to soar worldwide, increasing from 50million in 2018 to 152million in 2050, according to Alzheimer’s Research.
In the UK, some 850,000 people in the UK have dementia, which is likely to reach one million by 2025.
Cases have been growing over the past few decades, and scientists have taken an interest in pollution being a potential cause.
The University of Southern California study, published in Brain, looked at one of the main types of pollution – PM2.5 particles.
PM2.5 come from traffic exhaust, smoke and dust and their tiny size allows them to remain airborne for long periods.
They are about one 30th the width of a human hair, so small they can be inhaled into the lungs, enter the blood stream and travel to the brain.
Previous research has suggested fine particle pollution exposure increases the risk for Alzheimer’s and dementia as a whole. This is thought to be because tiny pollutants may cause inflammation – a problem which may trigger dementia.
A direct link has still not been found. And what scientists haven’t discovered is whether PM2.5 alters brain structure and accelerates memory decline.
Andrew Petkus, an assistant professor of clinical neurology at USC and a co-author of the study said: ‘This is the first study to really show, in a statistical model, that air pollution was associated with changes in people’s brains and that those changes were then connected with declines in memory performance.
‘This study provides another piece of the Alzheimer’s disease puzzle by identifying some of the brain changes linking air pollution and memory decline.
‘Each research study gets us one step closer to solving the Alzheimer’s disease epidemic.
‘Our hope is that by better understanding the underlying brain changes caused by air pollution, researchers will be able to develop interventions to help people with or at risk for cognitive decline.’
Dr Katy Stubbs, of Alzheimer’s Research UK, said there is a ‘pressing need’ to identify potential risk factors for dementia, considering one in people born today will develop it in their lifetime.
On the back of the findings she said: ‘The link between air pollution and dementia risk is a growing area of research.
‘This study links greater exposure to air pollution… but the study didn’t look at how many people actually went on to develop the disease.’
The research, led by Dr Diana Younan, used data from women aged 73 to 87 who had up to two brain scans five years apart as part of the Women’s Health Initiative, launched in 1993.
Those brain scans were compared with people who had Alzheimer’s, and scored on their similarity by a machine which had been ‘trained’ to learn Alzheimer’s patterns.
The researchers also gathered information about where the women lived to estimate their exposure to fine particle pollution.
The findings show a link between higher pollution exposure and progressive atrophy of grey matter in the brain, which processes information.
In Alzheimer’s, connections break down as neurons are injured and die throughout the brain. Many regions begin to shrink.
By the final stages of Alzheimer’s, this process – called brain atrophy – is widespread, causing significant loss of brain volume.
High pollution was also linked with memory problems, as women in the study also had annual memory test which measured their ability to recall information quickly and learn new things.
Alzheimer’s is thought to be largely caused by genetics, with smoking, obesity and lack of exercise increasing the risk.
But the findings took into account risk factors including lower income, education, race and cigarette smoking.
The findings are concerning considering the World Health Organisation (WHO) estimates 91 per cent of the world’s population lives in places where air quality exceeds WHO guideline limits.
Earlier this year, researchers at the University of New South Wales claimed cases of dementia are being propelled at a rate of more than 20 per cent a year due to toxic air.
Researchers from King’s College and St George’s, University of London last year found 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.
Fine particle pollution has already been blamed for cases of asthma, cardiovascular disease, lung disease and premature death.
More than 40,000 people in the UK are thought to die early every year because of air pollution.
There is currently no cure for Alzheimer’s, which is leading cause of death in the UK and sixth-leading cause in the US.
Dr Stubbs said: ‘The best evidence suggests that staying socially, mentally and physically active, eating a healthy balanced diet, not smoking, drinking only within the recommended limits and keeping weight, cholesterol and blood pressure in check are all good ways to support a healthy brain as we age.’