As the baby boomers age and the global population grows older, dementia rates are rising. Increasingly, we hear wellness advice focused on protecting cognitive health, including eating brain-healthy foods, exercising, managing stress, and engaging with others.
New research suggests that the quality of the air we breathe also has a significant impact on our cognitive health. A systematic review published earlier this year in The Lancet Planetary Health finds that exposure to outdoor air pollution significantly increases the risk of developing dementia.
The journal article is the most extensive review to date of the relationship between long-term air pollution exposure and dementia risk. It compiles data from 51 studies conducted in high-income countries in Europe, North America, Asia, and Australia, involving nearly 30 million participants.
Based on a complex statistical analysis, the researchers estimate that approximately 3 percent of dementia cases could potentially be prevented by eliminating air pollution exposure.
And they found that geography matters. For example, the data suggest that dementia risk would be approximately 9 percent lower in a city like Edinburgh compared with London, purely based on air pollution differences.
Researchers found three main sources of air pollution that affect cognitive health: fine particulate matter with diameters of 2.5 microns or less, primarily from vehicle exhaust; nitrogen dioxide released from vehicles and power plants; and black carbon produced by diesel engines, wildfires, and wood stoves.
Data show the risk of dementia increases as exposure level increases, especially for the tiny particulate matter, which is so small it can be inhaled deeply into the lungs.
What makes air pollution particularly dangerous is its invisibility. Unlike cigarettes or alcohol, we don’t choose to “consume” air pollution. Many people aren’t aware they are exposed to pollution, and, importantly, it doesn’t affect everyone equally.
“What’s particularly concerning for our aging population is that air pollution represents an invisible, involuntary risk factor that accumulates over a lifetime,” explained Karl Pillemer, a Cornell psychology professor and founding director of the Cornell Institute for Translational Research on Aging and the Aging and Climate Change Clearinghouse. Pillemer was not involved in this study. “Unlike modifiable behaviors such as diet or exercise, older adults have limited control over the air they breathe, especially if they’re aging in urban areas with poor air quality. We must expand our understanding of ‘aging well’ beyond individual lifestyle choices to include the environmental contexts in which people grow old.”
Marginalized communities often face disproportionate exposure to air pollution, yet tend to be underrepresented in research studies. In addition, this review does not include participants from lower-income countries, where air pollution is more prevalent. In those locations, the risk could be much higher than estimated in this report.
The problem may be worse than we currently understand. Separate research conducted by a researcher at the University of Lancaster has found there are even smaller particles inside human brain tissue. These nanoscale particles are so small that they can be transported directly into brain cells, where they cause inflammation, DNA damage, and cell death. These particles are associated with the characteristic amyloid plaques of Alzheimer’s disease.
Despite the strength of the connection between air pollution and dementia, researchers don’t fully understand how air pollution damages the brain. Unlike the cardiovascular effects of pollution, where mechanisms are well-understood through controlled experiments, the neurological pathways remain unclear.
Questions remain about the timing of exposure to pollution; some evidence suggests exposure later in life may increase the risk of dementia even more, but there are no firm conclusions yet. Researchers also don’t understand what types of dementia are most sensitive to pollution. Most of the current studies estimate exposure based on home addresses, which doesn’t provide a full picture of someone’s actual exposure to pollution.
Air pollution is a systemic problem that requires policy interventions. But individuals can take steps to protect themselves, primarily by choosing housing that offers better air quality whenever possible. They can also work on improving other risk factors for dementia, such as managing blood pressure, controlling diabetes, staying physically active, avoiding smoking, and maintaining social connections.
The take-home message: Data show a clear link between air pollution and dementia. This is a preventable risk factor that society can address with improved technologies and environmental policies.
