Meta-analysis: Air pollution may increase dementia risk

Key takeaways:

• Fine particulate matter, nitrogen dioxide and nitrogen oxide may be risk factors for dementia.
• The findings provide evidence for the regulation of particulate matter.

Air pollution may be a risk factor for dementia, according to the findings of a meta-analysis published in BMJ.

Elissa H. Wilker, ScD, assistant professor of medicine in the departments of epidemiology and environmental health at the Harvard T.H. Chan School of Public Health in Boston, and colleagues searched databases for studies that longitudinally followed adults to evaluate associations between dementia and U.S. Environmental Protection Agency-designated air pollutants and traffic pollution proxies.

In total, 51 studies were eligible for inclusion, most (n =38) of which assessed fine particulate matter (PM2.5). All studies were published in the past 10 years, with most (n =33) being published in or after 2020. Most were conducted in North America (n = 25).

Of these studies, 16 studies met inclusion criteria for meta-analyses, seven of which were from North America, six were from Europe and one was from Hong Kong.

Among 14 studies that assessed PM_2.5, there was a trend toward an increased risk for dementia with each 2 µg/m³ of PM_2.5 (overall HR = 1.04; 95% CI, 0.99-1.09).

There were nine studies that evaluated nitrogen dioxide (NO₂), five that assessed nitrogen oxide (NOx) and four that assessed ozone (O₃). Analyses showed a trend toward greater dementia risk per 10 µg/m³ NO₂ (HR = 1.02; 95% CI, 0.98-1.06) and per 10 µg/m³ NO_x (HR = 1.05; 95% CI, 0.98-1.13). There was no association between O₃ and dementia.

“This is a big step in providing actionable data for regulatory agencies and clinicians in terms of making sense of the state of the literature on this hugely important health topic,” Marc G. Weisskopf, PhD, ScD, lead author and Cecil K. and Philip Drinker Professor of Environmental Epidemiology and Physiology at the Harvard T.H. Chan School of Public Health, said in a press release. “The results can be used by organizations like the Environmental Protection Agency, which is currently considering strengthening limits on PM_2.5 exposure. Our findings support the public health importance of such a measure.”

References:

• Air pollution may increase risk for dementia. https://www.eurekalert.org/news-releases/984941. Published April 5, 2023. Accessed April 10, 2023.
• Wilker EH, et al. BMJ. 2023;doi:10.1136/bmj-2022-071620.