Long-term exposure to air pollution has been linked to an increased risk of developing dementia, according to a groundbreaking new study. The study, which was led by the University of Washington in the US, looked at data collected over an impressive 40-year period to come to its worrying conclusions. The researchers compared figures from a dementia investigation that began in the Nineties and compared it to air quality data dating back to the Seventies.
In total, the researchers looked at 4,166 volunteers in Seattle who have enrolled in the Adult Changes in Thought (ACT) Study.
By the end of the study, more than 1,000 of the volunteers developed dementia.
The researchers believe poor air quality and tiny particulate matter (PM2.5) is the culprit.
According to their findings, even a small increase of exposure to fine particulate matter (PM2.5) over a decade can greatly increase the risk of dementia.
Particulate matter is a term that describes solid particles and droplets of liquid less than 2.5 micrometres wide.
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These particles can include soot, dust, ash and the pollution emitted from car exhausts.
Rachel Shaffer, the study's lead author, said: "We found that an increase of one microgram per cubic metre of exposure corresponded to a 16 percent greater hazard of all-cause dementia.
"There was a similar association for Alzheimer’s-type dementia."
Although a direct link between different forms of dementia and air pollution has not yet been established, there is a growing body of evidence to suggest poor air quality plays a role.
According to the Alzheimer's Society, there is "a strong case for further research" into this worrying link.
The Head of Research at Alzheimer’s Research UK said today the Washington study adds more evidence to the link between pollution and dementia.
However, the expert warned it is "tricky" to unpack the various "complex lifestyle factors" that come into play.
Dr Sara Imarisio said: "We know that the diseases that cause dementia can begin up to two decades before symptoms appear.
"While this research looked at exposure to air pollution over 10 years, the volunteers had an average age of 75 at the start of the study, and future research should explore how air pollution throughout our lives may affect the risk of dementia."
A study published three years ago has come to a similar conclusion as the Washington paper, warning against exposure to nitrogen dioxide and microscopic particles.
And last week a report at the International Conference of the Alzheimer’s Association (AAIC) said improving air quality can lower the risk of developing Alzheimer's.
It is estimated dementia already affects more than 850,000 in the UK - that is one in 14 people above the age of 65.
Global cases are estimated at about 50 million and researchers fear the numbers are going to triple in the next 30 years.
Commenting on the Washington study, Dr Imarisio said: "While they worked to account for factors other than air pollution that may underly an association between where people live and their dementia risk, it is difficult to rule these out entirely.
"There are a number of biological explanations for why air pollution could be linked to an increased risk in dementia, but researchers didn't specifically look at these in this study."
However, the expert believes the study's findings are still relevant to the UK and the rest of the world.
Air pollution is believed to be one of the leading causes of asthma, lung disease and heart disease in the UK.
A 2019 report by the Department for Environment, Food and Rural Affairs (DEFRA) found pollutants like nitrogen oxides and metallic pollutants pose a risk to human health, welfare and the environment.
Dr Imarisio said: "As individuals, air pollution is a dementia risk factor that is hard to avoid but can be addressed by wider societal action and legislative change.
"The findings underline the importance that reducing air pollution should be a priority for public health authorities."