Air pollution has been a focus of several studies on cognitive impairment and dementia risk. There is evidence that tiny air pollution particles can enter the brain, but at this time, we can't say if they play a role in the development of dementia. There is a strong case for further research into the effect of air pollution on brain health.
What is air pollution?
Air pollution is comprised of several different components, including gases, chemical compounds, metals, and tiny particles known as particulate matter (PM). While this mix contains multiple hazardous ingredients, such as ozone, sulfur dioxide, and carbon monoxide, the element that seems most concerning for the brain is particulate matter fewer than 2.5 micrometers (PM2.5). PM2.5, also known as fine particulate matter, generally comes from smoke, dust, and vehicle exhaust. Long-term exposure or exposure to high levels of air pollution can be hazardous, leading to health conditions that affect the lungs and heart.
Does air pollution affect the brain?
Magnetite particles are released into the air by burning fuel, but they are also produced naturally in the brain. A study of brain tissue from people in Mexico City and Manchester conducted in 2016 confirmed that magnetite from air pollution can pass into the brain. Using a special electron microscope, the researchers examined the surface properties of the magnetite particles to prove that they had been generated at the high temperatures found in an engine rather than through natural processes. This study confirmed that fine particulate material could pass into the brain via the bloodstream or directly through the thin lining of the nose.
The particles were seen inside protein deposits called amyloid plaques which are abundant in the Alzheimer's brain, leading to speculation that magnetite could be involved in developing Alzheimer's disease. However, the study did not provide evidence that magnetite is involved in the formation of amyloid plaques or that it can lead to the death of brain cells. Alternatively, magnetite particles could enter the brain from polluted air and end up in amyloid plaques due to the brain's waste disposal processes.
Studies in mice have shown some effects of breathing polluted air on the brain. Mice exposed to polluted air collected from near busy roads show biological changes that are known to cause damage to the brain and an increase in levels of the protein amyloid, which is one of the indications of Alzheimer's disease. However, human brain imaging studies show that increased brain amyloid protein alone doesn't necessarily mean Alzheimer's disease will develop.
Could air pollution be a cause of dementia?
A direct link between air pollution and Alzheimer's disease has not been found. However, there are many questions still unanswered. A growing number of studies looking at exposure to pollution from around the world combined with increasingly sophisticated techniques for seeing the fine particulate matter in the brain and body is creating a case for further research.
Studies of mice and dogs living in polluted areas suggest that air pollution could be associated with cognitive impairment. Exposure of mice and rats to traffic pollution in the lab resulted in symptoms such as poorer learning ability, memory, and motor skills. In people there are a couple of studies showing that those who are exposed to high levels of pollutants perform poorer on cognitive tests over time, but this does not mean they have or will develop dementia.
The most convincing evidence comes from a study of 6.6 million people from Canada published in 2016 that reported a potential link between dementia and living close to busy roads. The study found that those living within 55 yards of a major road were 7% more likely to develop dementia than those living more than 335 yards away, where fine PM levels can be ten times lower.
As other factors are associated with living on a busy road, such as high noise pollution and stress, this study doesn't prove that air pollution causes dementia. However, it does suggest that the study of air pollution and dementia should be prioritized for future research.
Air pollution levels in Wisconsin
The good news is that the overall air quality in Wisconsin continues to improve, according to the 2021 Wisconsin Air Quality Trends Report. The report, which includes air quality data through 2019, finds that concentrations of most pollutants for which the Environmental Protection Agency (EPA) has set national air quality standards have decreased in all state regions since monitoring began.
Due to these significant reductions, 95 percent of Wisconsin's population lives in areas meeting all federal air quality standards.
The shoreline along Lake Michigan has historically been an area of high ozone pollution. However, this has gradually been decreasing, and it is now almost 25 percent lower than it was 20 years ago. Among other reductions recorded were an 89 percent drop in sulfur dioxide and a 60 percent reduction in carbon monoxide emissions. These reductions have been attributed to a more fuel-efficient system of using fossil fuels and more efficient engines in road vehicles.
Should I be worried about the effect of air pollution on my brain?
Unlike the link between air pollution and heart or lung health, for which there is much evidence, the effect on the brain and cognitive health is less clear. Much more research is needed to show whether there is a link, how strong it might be, and precisely what is causing the association. The evidence so far makes a case for investment in long-term, well-controlled studies to understand the risks of exposure to different pollution levels.
Other lifestyle factors are known to have a more significant influence on the risk of developing dementia than air pollution.