Time to clear the air on pollution and dementia

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By Lorik Zhubi | Friday 25 August 2023

In recent years, it’s become increasingly clear that greater exposure to air pollution is linked to a greater risk of developing dementia. In 2020, the influential Lancet Commission included pollution as one of 12 risk factors linked to the condition. And in 2022, a government committee ruled that it was ‘likely’ that air pollution contributes to the UK’s dementia rates.  

Since then, the evidence has continued to build on the link between the air we breathe, and our risk of developing dementia in later life.  

And just this month, two new studies have added to this understanding. First, a study from the US looked into how different sources of air pollution contribute to dementia. And then a UK-based study found that air pollution also seems to impact people already living with dementia, especially those with vascular dementia 

Let’s look at the new studies, and how they reinforce the case for urgent government action to improve the quality of the air we breathe.  

The source of the problem 

The first study, published earlier this month in the journal JAMA Internal Medicine by a group of US researchers, investigated the links between a common air pollutant, known as PM2.5, and dementia. What’s unique about this study is that it focussed on the sources of PM2.5 and their individual effect on dementia risk.  

The researchers looked at data from an ongoing health study of nearly 40,000 people, including information about whether they developed dementia, and where in the US they lived. They then cross-referenced this with detailed regional information about air pollution levels and sources, to see if changes in local air pollution levels correlated with whether people living there were more or less likely to develop dementia.  

As well as confirming a link between air pollution and dementia, the researchers observed that different air pollution sources had different levels of influence on the condition. While most of us associate air pollution with industry and traffic, this new research also pointed a finger at agriculture – and specifically at a gas called ammonia, which is released when animal manure is broken down by bacteria, and which then reacts with gases in the atmosphere to form PM2.5. The researchers found that PM2.5 emissions linked to agriculture had the strongest link with developing dementia later in life. PM2.5 emissions from wildfires also had a strong effect.  

It’s important to note that this research was a so-called ‘observational’ study, meaning that it has only revealed a correlation between PM2.5 emissions, and dementia risk, rather than definitively proving cause and effect. However, the findings relating to agriculture are particularly pertinent for the UK. That’s because while ammonia use in US agriculture accounts for 30% of PM2.5, research suggest that it accounts for 60% of total PM2.5 in the UK. 

Understanding the effects of different sources is important. As our Executive Director of Research and Partnerships, Dr Susan Kohlhaas, told the media “Poor air quality doesn’t affect all sectors of society equally. Some communities are affected more than others.” Knowing which ones, she said, “is vital to developing targeted interventions that have the biggest impact on at-risk communities, for example those who work in agriculture or who are exposed to wildfires,”.  

It’s hard to shy away from the devastation that wildfires are causing the planet, and we expect more evidence surrounding PM2.5 emissions from wildfires in the future to further build our understanding in this area. 

Impact on people living with dementia 

While most research to date has focused on air pollution’s link to developing dementia, less attention has fallen on its impact on people who already have the condition. Published in the same week as the US study, a separate UK study found that exposure to the most common forms of air pollution – nitrogen dioxide (NO2) and particulate matter – was linked to increased use of mental health services by people living with dementia.  

The researchers looked at community mental health service use over nine years by over 5,000 people with dementia aged 65 and over. All participants lived in four boroughs of south London – Croydon, Lambeth, Lewisham or Southwark – after initially being diagnosed with dementia between 2008 and 2012. 

The findings, published in BMJ Mental Health, showed that those living in areas with higher levels of NO2 were 27% more likely to use community mental health services than those living in areas with the lowest levels, while those exposed to the highest levels of particulate matters were 33% more likely to use them. 

“As you increase the dose of air pollution, the likelihood of using community mental health teams increased as well,” lead author Dr Amy Ronaldson, research fellow at the Institute of Psychiatry, Psychology and Neuroscience at King’s College London, told the i newspaper 

The effects appeared stronger for people with vascular dementia than other forms of dementia. Dr Susan Mitchell, Alzheimer’s Research UK’s Head of Policy, said the findings provided one of the first demonstrations of poor air quality’s “knock-on effect” on already over-stretched health services and the lives of people living with dementia.  

There is still so much to uncover 

As the links between air pollution and dementia continue to mount, it’s important that there is a research focus on understanding what mechanisms are at play. “There are several biological explanations that could be behind the link between air pollution and dementia,” said Dr Kohlhaas – a sentiment echoed by Dr Mitchell: “As well as urgent action to bring levels down, there is a pressing need to find out more about exactly how air pollution affects dementia risk,” she said.  

That’s why we’re funding the work of researchers like Dr Jake Brooks, who is helping to unravel how certain air pollution particles enter the brain and cause Alzheimer’s disease. “There’s growing body of evidence that suggests air pollution could also be putting us at a greater risk of developing dementia, but we don’t know how this happens,” he told us. “My research aims to show how tiny metal-containing pollution particles may accumulate and distribute in the brain, and how they associate with Alzheimer’s disease proteins like tau and amyloid.”  

While researchers like Dr Brooks continue to explore the underlying mechanisms, our current understanding is more than enough reason for government to act. Unfortunately, action seems to be happening far too slowly.  

“This government is dragging its feet on implementing stricter air quality standards, with a plan to reach 10 µg/m3 PM2.5 by 2040,” said Dr Mitchell. “We think that’s a decade too late. By that time, there will be an estimated 1.2 million people living with dementia in the UK, many of whom will have been exposed to unacceptable levels of air pollution while the government fails to act”.  

The benefits of addressing air pollution for at-risk communities are two-fold. It will lower their risk of developing dementia, and it will improve the everyday lives of people already living with the condition.  

And if this wasn’t enough reason for government already, effective action on air pollution could alleviate the stress put on NHS services, like mental health resources, by reducing demand from those with dementia. This could also lower the health damages associated with air pollution, which is estimated to be nearly £6bn for the period of 2017-2025.  

We want to see the government being far more ambitious, more forward thinking, and to commit to achieving 10 µg/m3 PM2.5 by 2030.  

For the sake of people living with dementia now, and those at risk of developing it in the future, it can be done, and it should be.  

  • Learn more about the links between air pollution and dementia from Dr Mitchell, Dr Brooks and others in the field, at our public online event, Lab Notes, on August 31st at 12pm. Register here: https://tinyurl.com/2p6dfuca 

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About the author

Lorik Zhubi

Policy Communications Officer