Summary of Harvard Scientists Reveal That Air Pollution May Increase Risk of Dementia:
A new Harvard T.H. Chan School of Public Health meta-analysis suggests that exposure to fine particulate air pollutants (PM2.5) may be linked to an increased risk of dementia. The study is the first systematic review and meta-analysis to use the new Risk of Bias In Non-Randomized Studies of Exposure (ROBINS-E) tool. It incorporates more recent research utilizing “active case ascertainment.” The researchers found consistent evidence of an association between PM2.5 and dementia, even when annual exposure was less than the current EPA annual standard of 12 micrograms per cubic meter of air (μg/m3). The researchers noted that air pollution’s estimated association with the risk of dementia is smaller than that of other risk factors, such as education and smoking. Still, the population-level health implications could be substantial because of the number of people exposed to air pollution.
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Air Pollution Linked to Increased Risk of Dementia, New Meta-Analysis Finds
A new Harvard T.H. Chan School of Public Health meta-analysis found a potential link between exposure to fine particulate air pollutants (PM2.5) and an increased risk of developing dementia. The study is the first to use the new Risk of Bias In Non-Randomized Studies of Exposure (ROBINS-E) tool, which addresses bias in environmental studies in greater detail than other approaches. It incorporates more recent research utilizing “active case ascertainment.”
Findings Support Strengthening Limits on PM2.5 Exposure
Led by Marc Weisskopf, Cecil K., and Philip Drinker, Professor of Environmental Epidemiology and Physiology, the study was undertaken by scanning over 2,000 studies and identifying 51 that evaluated an association between ambient air pollution and dementia, all published within the last 10 years. Sixteen of these studies met the meta-analysis criteria, with most research concerned with PM2.5. The researchers found consistent evidence of an association between PM2.5 and dementia, even when annual exposure was less than the current EPA annual standard of 12 micrograms per cubic meter of air (μg/m3).
“This is a big step in providing actionable data for regulatory agencies and clinicians to make sense of the state of the literature on this hugely important health topic. The results can be used by organizations like the Environmental Protection Agency, which is currently considering strengthening limits on PM2.5 exposure,” said Weisskopf. “Our findings support the public health importance of such a measure.”
Air Pollution May Be a Potentially Modifiable Risk Factor Linked to Dementia
While the estimated risk of dementia linked to air pollution is smaller than other risk factors, such as education and smoking, the sheer number of people exposed to air pollution still has a significant population-level health impact. Over 57 million people worldwide live with dementia, with estimates suggesting that the number will increase to 153 million by 2050. Air pollution is a potentially modifiable risk factor for the disease.
“Given the massive numbers of dementia cases, identifying actionable modifiable risk factors to reduce the burden of disease would have tremendous personal and societal impact,” Weisskopf said. “Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors—but more importantly through regulation.”
The Studies Included in the Meta-Analysis
The research was assessed using ROBINS-E, which addresses bias in environmental studies in greater detail than other approaches, and the active case ascertainment technique, which involves screening entire study populations, followed by face-to-face dementia evaluations of participants who did not have dementia at baseline. Of the studies used in the meta-analysis, nine used active case ascertainment. The researchers found a 17% increase in the risk of developing dementia for every 2 μg/m3 increase in average annual exposure to PM2.5.
Although the majority of the research in the meta-analysis concerned PM2.5, the study also found evidence suggesting associations between dementia and nitrogen oxide (5% increase in risk for every 10 μg/m3 increase in annual exposure) and nitrogen dioxide (2% increase in risk for every 10 μg/m3 increase in annual exposure), although the data was more limited.
Conclusion
Air pollution is a potentially modifiable risk factor for dementia, and identifying actionable modifiable risk factors to reduce the burden of dementia would have tremendous personal and societal benefits. While the estimated risk of dementia linked to air pollution is smaller than other risk factors, the population-level health implications are significant. The study’s findings support the public health importance of proposals currently under consideration by the Environmental Protection Agency to strengthen limits on PM2.5 exposure.
