Air pollution likely to be causing dementia, say UK science advisers

Air pollution is likely to be contributing to dementia and a declining mental ability in older people around the world, science advisers to the UK government have said for the first time.

The opinion from the authoritative Committee on the Medical Effects of Air Pollutants (COMEAP) adds significant weight to a growing number of studies linking dirty air to cognitive decline.

In a report published today, the group said that after reviewing nearly 70 studies it had concluded the evidence now suggested an association between exposure to air pollutants and “an acceleration of the decline in cognitive function often associated with ageing, and with the risk of developing dementia.” To date, air pollution has largely only been firmly linked to physical health impacts on the lungs, heart and other organs.

Frank Kelly at Imperial College London, who started working on the report three years ago, says the amount of research suggesting a link to mental decline had “snowballed” in recent years. “Dementia is one of the greatest, if not the greatest, global challenge for health and social care in the 21st century,” he says.

The committee said that it couldn’t put a number on how many older people had seen a mental decline linked to air pollution, largely due to a scarcity of investigative studies that might provide causal evidence. However, Kelly says that a 2018 study of people in London indicated roughly 60,000 of the 209,600 new cases of dementia in the UK each year could be due to poor air quality.

The report identifies three main mechanisms for how air pollution could be accelerating mental declines. Chief among these is the damage done to blood vessels by tiny particulate matter, which can affect blood supply to the brain: dementia can result from a reduction in blood supply to brain cells. There are a number of human, as well as animal, studies showing the effect pollution can have on blood vessels.

More tentative explanations include the brain’s immunological system being activated by exposure to pollution and the very smallest particles directly reaching the brain via the nasal passage and the nerve cells that give our sense of smell, the olfactory bulb. The evidence for these other two mechanisms is slimmer, and the committee has much higher confidence in the blood vessel one, says Kelly.

“Thanks to an immense amount of work in the last several years, we can say with confidence this link exists,” says Brian Castellani at Durham University, who was not involved in the report. It shows exposure to dirty air in early life can have significant later-life impacts on brain health, he says.

Stefan Reis at the UK Centre for Ecology and Hydrology says: “The findings of COMEAP are not surprising, but add further weight to the understanding that air pollution health impacts are much wider and likely more profoundly affecting public health beyond the traditionally known immediate effects.”

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