Exposure to air pollution is linked to an increased risk of dementia, even at levels below UK, US and EU air quality standards, according to research. Experts say the findings add to the need for urgent action to reduce exposure to pollution globally.
More than 57 million people worldwide are living with dementia and the global burden continues to increase. But interventions to delay or prevent the onset of dementia are scarce.
Accumulating evidence suggests air pollution may contribute to the risk of developing dementia. Experts at the Harvard TH Chan School of Public Health in the US looked at 14 studies examining the link between dementia and exposure to fine particulate matter (known as PM2.5). Fine particulate matter is an air pollutant made up of tiny pieces of solid or liquid substances, which are inhaled by people as they breathe.
The researchers’ analysis suggests that for every two micrograms per cubic metre increase in average annual PM2.5 concentration, the overall risk of dementia rises by 4%. Their findings are published in the BMJ journal.
More limited data suggests that exposure to nitrogen dioxide and nitrogen oxide gases – which are produced by the burning of fossil fuels – may also be a risk factor for dementia. The research did not find an association between ozone – a gas formed in the air due to reactions between pollutants – and dementia.
Although uncertainties remain, and caution is needed when interpreting the findings, the researchers said the results “strengthen the evidence that air pollutants are risk factors for dementia”.
In a linked editorial, experts from University College London in the UK warned that air pollution had the “potential to substantially affect dementia risk”.
They wrote: “Current estimates suggest that PM2.5 concentrations in major cities vary considerably from below 10 micrograms per cubic metre in some cities (eg Toronto, Canada) to more than 100 micrograms per cubic metre in others (eg Delhi, India), therefore, air pollution has the potential to substantially affect dementia risk globally.”.
They highlight that air pollution is also linked to an increased risk of other health conditions, with an estimated 6.5 million deaths attributable to air pollution each year.
“Although individuals can take steps to reduce their own personal exposure, for example, by remaining indoors on high air pollution days, this solution is impractical in the long term, so for many people, the risk is inescapable,” they added.
“[The] findings therefore add urgency to the need for effective policy measures to reduce air pollution globally.”
Dr Susan Mitchell, head of policy at Alzheimer’s Research UK, a charity that was not involved in the study, said: “Poor air quality is a significant public health issue, and this new review helps to cement the relationship between certain types of air pollution and dementia risk.
“But as individuals there’s little we can do about the air we breathe. So it’s vital the government leads from the front in reducing air pollution and the resulting harm to our brain health.
“But what we have seen so far has fallen disappointingly short. In December, the government missed a clear opportunity for decisive action on air pollution by setting an unambitious and inadequate target of 10 micrograms a cubic metre by 2040 – far less stringent than what Alzheimer’s Research UK and the World Health Organization recommended.
“The government should now ensure brain health is central to its major conditions strategy and its wider ambitions for prevention, and invest in population-level interventions that have significant impact on air pollution.
“What remains to be uncovered is the ‘how’ – there are several biological explanations that could be behind the link between air pollution and dementia, and we echo the authors’ call for more research to better our understanding in this area.”
