Temporary rises in air pollution may impair memory and thinking in older men, according to research that indicates even short-term spikes in airborne particles can be harmful to brain health.
Scientists found that the men’s cognitive performance fell following rises in air pollution during the month before testing, even when peak levels remained below safety thresholds for toxic air set by the World Health Organization and national regulators.
The findings build on growing evidence that exposure to fine particulate matter in the air, largely from road vehicles and industry, is harmful not only to the heart and lungs, but also to delicate neural tissues in the brain.
Researchers in the US and China compiled multiple cognitive test scores from nearly 1,000 men living in the Greater Boston area and checked them against local levels of PM2.5s – airborne particles smaller than 2.5 micrometres across. The men involved in the study were white and had an average age of 69.
Writing in Nature Aging, the scientists describe how higher levels of PM2.5s up to four weeks before testing were linked to poorer cognitive performance on tasks ranging from word memory to number recall and verbal fluency. The effect was clear even when concentrations of PM2.5s stayed below 10 micrograms per cubic metre, the WHO guideline level which is routinely breached in London and many other cities.
Intriguingly, the study found evidence that test scores were less affected by short-term rises in air pollution if the men were taking aspirin or other non-steroidal anti-inflammatory drugs, known as NSAIDs. “Our study indicates that short-term air pollution exposure may be related to short-term alterations in cognitive function and that NSAIDs may modify this relationship,” the authors write. According to one line of thinking, such painkillers may help by reducing inflammation that is triggered by fine particles getting into the brain.
While the WHO says levels of PM2.5s should not exceed an annual mean of 10 micrograms per cubic metre, the UK has adopted a higher limit of 25 micrograms per cubic metre. The government’s air quality index regards PM2.5 levels below 35 micrograms per cubic metre as “low”.
Last month, Philip Barlow, the inner south London coroner who concluded that air pollution was a cause of the death of nine-year-old Ella Kissi-Debrah, said the UK must adopt lower legally binding levels for particulate air pollution.
The impact of toxic air on respiratory and cardiovascular health is well-established and evidence for damage to the brain is mounting. Studies have linked air pollution to reduced intelligence and dementia. In February, work led by Prof Jamie Pearce at Edinburgh University found that exposure to air pollution in childhood was linked to poorer thinking skills in later life.
“The findings really stress the impact that air pollution is having on human health,” said Dr Joanne Ryan, head of biological neuropsychiatry and dementia research at Monash University in Melbourne, who was not involved in the latest work. “The importance of this study is that the findings align with a potential causal link of air pollution on brain function and they suggest that it is not just the very high levels of prolonged pollution that are concerning. The study found that even relatively low levels of air pollution can negatively impact cognitive function, and over possibly short periods of time.”
“This work confirms that there is a link between air pollution and how well the ageing brain works,” said Andrea Baccarelli, a senior author on the study and professor of environmental health sciences at Columbia University in New York. “These shorter-term effects are reversible: when air pollution clears, our brain reboots and starts working back to its original level. However, multiple occurrences of these higher exposures cause permanent damage.
“Our findings do not suggest yet that all older people should be on anti-inflammatory drugs, because these are medications with side-effects we cannot take lightly,” he added. “More holistically, reducing inflammation through a healthy diet, such as more fruit, vegetables, and fibre, or having regular physical exercise, can go a long way not only to make us generally healthier but also to make us more resilient against environmental threats such as air pollution.”