According to a groundbreaking study from Harvard T.H. Chan School of Public Health, exposure to fine particulate air pollutants (PM2.5) may significantly increase the risk of developing dementia.
This is a major development in terms of providing actionable data for regulatory agencies and clinicians, who can use this information to help limit exposure to these dangerous pollutants. The study is the first of its kind 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 assessment approaches.
Finding of this research is crucial given the massive numbers of dementia cases worldwide, estimated to reach 153 million by 2050, with up to 40% of cases thought to be linked to modifiable risk factors such as exposure to air pollutants.
Marc Weisskopf, the lead author of the study, emphasises the importance of identifying modifiable risk factors to reduce the burden of disease, given the tremendous personal and societal impact of dementia.
The study evaluated over 2,000 studies, identifying 51 that evaluated an association between ambient air pollution and clinical dementia, all published within the last 10 years. Sixteen studies met the criteria for meta-analysis, with PM2.5 being the most commonly studied pollutant. 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 metre of air (μg/m3). In particular, among the studies using active case ascertainment, the researchers found a 17% increase in risk for developing dementia for every 2 μg/m3 increase in average annual exposure to PM2.5.
Evidence has also been found 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), though the data was more limited.
While air pollution’s estimated association with the risk of dementia is smaller than that of other risk factors such as education and smoking, the population-level health implications could still be substantial, given the number of people exposed to air pollution.
The study’s findings have significant implications for regulatory agencies like the Environmental Protection Agency, which is currently considering strengthening limits on PM2.5 exposure. Personal behaviour can also modify exposure to these pollutants, but regulation is critical to ensure that the population’s health is protected. The study will be published in The BMJ and is a major step forward in understanding the link between air pollution and dementia.
Source: Harvard T.H. Chan School of Public Health.