The Overlooked Risk Factor for Dementia: Experts Reveal 17% Increase in Risk

Dementia is not a singular condition, but rather an umbrella term, similar to heart disease, that encompasses a broad range of specific medical disorders, such as Alzheimer’s disease. These conditions fall under the general category of “dementia” due to abnormal changes in the brain that lead to a decline in cognitive abilities, resulting in difficulties in daily activities and independent functioning. They can also impact a person’s behavior, emotions, and relationships.

While most brain changes related to dementia are irreversible and worsen over time, some cognitive problems caused by certain conditions, such as depression, medication side effects, excessive alcohol consumption, thyroid issues, and vitamin deficiencies, may improve with proper treatment or attention.

A recent meta-analysis conducted by Harvard T.H. Chan School of Public Health has revealed that individuals exposed to fine particulate air pollutants (PM2.5) may face an elevated risk of developing dementia.

According to the authors, this research is the first systematic review and meta-analysis to employ the novel Risk of Bias In Non-Randomized Studies of Exposure (ROBINS-E) tool, which addresses biases in environmental studies in greater depth than other assessment approaches. It is also the first study to incorporate newer research that employed “active case ascertainment,” a technique that entails screening entire study populations and then conducting in-person assessments for dementia among individuals who did not have dementia at the start of the study.

The findings were just published in The BMJ.

Currently, over 57 million individuals globally are afflicted with dementia, and estimates predict that this number will escalate to 153 million by 2050. As many as 40% of these cases may be linked to modifiable risk factors, including exposure to air pollutants.

The study’s authors, Marc Weisskopf, Elissa Wilker, and Marwa Osman, systematically reviewed more than 2,000 studies, identifying 51 that examined the association between clinical dementia and ambient air pollution published in the past decade. The authors used ROBINS-E to assess bias in these studies, and 16 of them met the criteria for inclusion in the meta-analysis. The majority of the research centered on PM2.5, with nitrogen dioxide and nitrogen oxide being the next most common pollutants studied. Of the studies used in the meta-analysis, nine employed active case ascertainment.

The study discovered consistent evidence of a connection between PM2.5 and dementia, even when yearly exposure was lower than the current EPA annual standard of 12 micrograms per cubic meter of air (μg/m3). Specifically, among the studies that utilized active case ascertainment, the researchers found a 17% higher risk of developing dementia for each 2 μg/m3 increase in average annual exposure to PM2.5. The data also suggested a relationship between 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) with dementia, although the evidence was less comprehensive.

While examining the association between air pollution and the risk of developing dementia, the researchers acknowledged that air pollution’s estimated connection with dementia risk is relatively weaker than other risk factors, including smoking and education. Nevertheless, given the vast number of individuals exposed to air pollution, the potential health implications at the population level could be significant.

“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 added. “Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors—but more importantly through regulation.”

Source: 10.1136/bmj-2022-071620

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