A joint China-US research team has found that exposure to even short-term air pollution may impair cognitive function.

Air pollution is a growing cause of sickness and death globally, with a recent study estimating that it caused an extra 8.8 million premature deaths in 2015, surpassing the 7.2 million caused by tobacco smoking. It has well-established effects on the lungs and the heart – it has been linked with spikes in heart attacks, strokes and asthma, and is a carcinogen known to cause lung cancer.

Increasingly, research is also associating air pollution with other health impacts including kidney disease, psychiatric illness and Alzheimer’s.

What causes air pollution?

• Air pollution is the release of pollutants into the air that have detrimental effects on human or planetary health.
• It can have natural sources, such as desert dust or bushfire smoke, but is increasingly created by humans, primarily from burning fossil fuels.
• There are two main types: smog occurs when emissions from burning fossil fuels react with sunlight, while soot is made up of tiny particles made up of smoke, soil, dust, allergens or chemicals. Anything that combusts fossil fuels can cause this, including vehicle exhaust, power plants, incinerators and more.

Now, in a new study published in the journal Nature Ageing, researchers have linked poor air quality with decreased brain health.

The team studied a sample of 954 Caucasian males (with an average age of 70) from the Boston area in the US, who were participants in the Veterans Affairs Normative Aging Study. Their cognitive function was measured by a series of assessments to test their attention, learning and memory, as well as an screening to help detect early signs of dementia.

This was compared to the average levels of fine particulate matter (PM2.5, smaller than 2.5 micrometres in size) in the area, both on the day of each test and in the 28 days prior. The team found the participants tended to score lower when levels of PM2.5 were higher in the month before the tests – even when levels were still below what is considered as “hazardous”.

“The findings were quite startling,” write cognitive health researchers Joanne Ryan and Alice J. Owen, in an accompanying article. “Even relatively small increases in the levels of PM2.5 in the 3–4 weeks prior to testing were associated with consistently worse cognitive performance.”

Ryan and Owen, both from Monash University in Australia and both not involved in the study, point out that Boston “has by no means the worst air quality in the USA or the world, and yet significant detrimental effects of air pollution on cognitive function were observed”.

While a decline in brain function in older adults is common, it can be exacerbated – and accelerated – by environmental factors. Evidence is mounting that air pollution could be a risk factor for dementia and could, over the long term, be associated with cognitive declines.

“The results of the current study are especially important because they provide some of the first evidence that even relatively low-level, short-term increases in PM2.5 are detrimental for thinking and memory, as well as global cognition in older adults,” Ryan and Owen write.

The results may point to a general trend in the larger population, given that air pollution affects brain development in kids, and women seem to be more strongly affected than men.

Interestingly, the researchers also found that the participants who were prescribed NSAIDs (nonsteroidal anti-inflammatory drugs, such as aspirin) were less adversely affected. This may be because the health impacts of air pollution tend to involve activating the body’s inflammatory response. But caution is warranted; there may be many other differences between participants who do and don’t use NSAIDs.

This study also had a relatively small sample size and focused on a certain geographical area, so further research is needed to solidify the link between air pollution and cognitive function.

However, Ryan and Owen emphasise the importance of the results.

“The implications for public health, and consequent health, societal and economic costs of air pollution, are immense,” they write. “This should be a further wake-up call about the urgent need for action.

“It has been estimated that 90% of the world’s population breathe polluted air. Breathing clean air is fundamental to our health but represents a global challenge and one of substantial inequity, disproportionally affecting the most vulnerable.”

Image credits: Getty Images