The Risk Of Dementia Could Be Raised By Air Pollution Exposure

A recent meta-analysis conducted by Harvard T.H. Chan School of Public Health suggests that the exposure to fine particulate air pollutants (PM2.5) could enhance the chances of developing dementia.

Lead author Marc Weisskopf, who is the Cecil K. and Philip Drinker Professor of Environmental Epidemiology and Physiology, stated “that the study is a significant milestone in supplying valuable data for regulatory agencies and clinicians to better comprehend the current state of literature on a critical health issue. The study’s outcomes can be important for some organizations such as the Environmental Protection Agency, which is evaluating the possibility of increasing restrictions on PM2.5 exposure“. According to Weisskopf, “the findings emphasize the importance of this measure for public health”.

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The particularity of this study lies in its utilization of the innovative Risk of Bias In Non-Randomized Studies of Exposure (ROBINS-E) tool during the primary systematic review and meta-analysis. This method offers a more thorough approach in addressing bias in environmental studies compared to other assessment techniques. Furthermore, it incorporates the most recent studies that adopted an “active case ascertainment” technique, which entails screening entire study populations, followed by in-person evaluation for dementia among participants who did not display signs of the condition at the beginning of the study. The BMJ journal will publish the research findings.

Dementia, a worldwide problem

Presently, over 57 million individuals worldwide are suffering from dementia, and projections indicate that this figure will rise to 153 million by 2050. Up to 40% of these cases are believed to be associated with potentially controllable risk factors, including exposure to air pollutants.

In the last decade, Weisskopf, Elissa Wilker, a researcher in the Harvard Chan-NIEHS Center for Environmental Health, and Marwa Osman, a doctoral student in the Biological Science in Public Health program, reviewed more than 2,000 studies and selected 51 studies that investigated the correlation between environmental air pollution and clinical dementia.

After evaluating those studies for bias with ROBINS-E, the researchers discovered that 16 of them satisfied the requirements for the meta-analysis. The majority of studies had its concentration on PM2.5, with nitrogen dioxide and nitrogen oxide being the second most frequently analyzed pollutants. Of the studies included in the meta-analysis, nine employed the active case ascertainment approach.

The research team discovered consistent evidence demonstrating a link between PM2.5 exposure and dementia, even when the annual exposure was below the current EPA standard of 12 micrograms per cubic meter of air (μg/m3). In particular, the scientists found that in studies that utilized active case ascertainment, for every increase of 2 μg/m3 in average yearly exposure to PM2.5, there was a 17% higher chance of developing dementia.

Furthermore, the researchers discovered indications of associations between dementia and nitrogen oxide (with a 5% greater risk for every 10 μg/m3 increase in annual exposure) and nitrogen dioxide (with a 2% greater risk for every 10 μg/m3 increase in annual exposure), although the data was not as comprehensive.

Solution to the problem of dementia

The scientists observed that the connection between air pollution and the probability of developing dementia is not as significant as the association with other risk factors like smoking and education. Nonetheless, considering the large number of individuals exposed to air pollution, the overall impact on public health could be considerable.

According to Weisskopf, “discovering modifiable risk factors that can be addressed to reduce the impact of the disease would have a significant effect on both individuals and society, given the high incidence of dementia cases. Although individuals can influence their exposure to PM2.5 and other air pollutants by adjusting their behavior, the most efficient method to tackle this issue is by regulating these pollutants.”

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