Longevity Briefs: Is Air Pollution Destroying Your Brain?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

The world’s population is growing older, and with that comes a rising prevalence of age-related cognitive decline and dementia. While age-related cognitive decline is currently unavoidable, it does seem to be modifiable. Some people remain relatively sharp in old age and die free of neurodegenerative diseases, while others develop early-onset dementia. One potential risk factor for cognitive decline is exposure to air pollution, particularly exposure to particulate matter (PM) – microscopic particles of solid or liquid pollutants suspended in the air. PMs may enter the lungs and trigger chronic inflammation, thought to be an important component of ageing. Smaller particles may even be able to enter the brain and cause neuroinflammation directly. In this study, researchers take a closer look at how higher PM levels affect different aspects of cognition in different age groups over different timescales.

The discovery:

Researchers analysed data from the Lifestyle and Healthy Aging of Chinese Square Dancer Study. This study included 2,668 women aged 45 to 82, recruited from seven major Chinese cities. Researchers then used precise location data to estimate exposure to PM2.5 and PM10 over 1 to 3 years. PM2.5 and PM10 refer to particulate matter with a diameter of under 2.5 or 10 micrometres, respectively. Data on other air pollutants like sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) were also collected, so that these exposures could be adjusted for in an attempt to isolate the effects of PM2.5 and PM10.

Participants underwent a series of tests to assess global cognitive function and four specific cognitive domains: memory (Auditory Verbal Learning Test – AVLT), language (Animal Verbal Fluency Test – AFT), attention (Digit Symbol Substitution Test – DSST), and executive function (Trail Making Test-B – TMT-B). They found that higher three-year exposure to both PM2.5 and PM10 was associated with significantly lower global cognitive function, with older age groups being more strongly affected. Both PM2.5 and PM10 were also associated with significant drops in all four cognitive domains, though statistical significance wasn’t always consistent between the age groups. Overall, attention (DSST) was the most consistently impacted score by both PM2.5 and PM10 exposure, with a significant negative association detected in the youngest participants (under age 60) for both types of particulate matter.

When researchers looked at 1-year exposure, there were fewer statistically significant relationships, but some significant associations remained in the older age groups, particularly for attention (DSST).

The implications:

This study provides more evidence that long-term exposure to particulate matter significantly impairs cognitive function. It also suggests that even short-term (1 year) exposure to higher PM levels could potentially have a significant impact on cognition, particularly in older age groups. While PM levels in China and other Eastern and Southern Asian countries are among the highest in the world, research has suggested that even levels below WHO recommendations are likely to be harmful long-term. The findings on short term impacts might even have implications for travellers to more polluted regions.

While this study took steps to control for confounding factors, it can’t entirely rule out the possibility that participants exposed to higher PM levels were also exposed to other, unmeasured environmental factors that contribute to cognitive decline. One such factor is temperature, which correlates with PM levels, but has been suggested by some studies to accelerate ageing.