New research from the University of Michigan suggests that air pollution emanating from bushfires and agricultural activities is toxic for the human brain and may increase risk of dementia.

The findings of the study by Boya Zhang and Sara Adar, environmental epidemiology researchers at U-M’s School of Public Health reveal that the release of harmful emissions at high concentrations from wildfires and farming practices impacts the cognitive health of those exposed to the pollution, making them more susceptible to dementia.

“We saw in our research that all airborne particles increased the risk of dementia but those generated by agricultural settings and wildfires seemed to be especially toxic for the brain,” says Adar, associate chair of the Department of Epidemiology in the School of Public Health, who currently leads several large cohort studies on the impacts of exposures on cognitive aging and dementia. Therefore, lowering particulate matter air pollution levels, even in a relatively clean country like the United States, may reduce the number of people developing dementia in late life, she added.

Adar led a team of researchers from U-M’s School of Public Health and the U-M Health System along with Boston University, the University of Washington, Georgetown University and the University of Southern California. Their study appears in the Journal of the American Medical Association’s Internal Medicine.

“This work suggests that particulate matter air pollution from agriculture and wildfires might be more neurotoxic compared with other sources. However, more research is needed to confirm these effects, especially for these two sources, which have received less attention in prior research,” said Zhang, a research fellow who focuses on the effects of air pollution on cardiopulmonary disease and cognitive aging.

Given that dementia develops over a long period of time, the study mainly aimed to provide evidence for policymakers to reduce exposures to these sources of emissions, she explains.

The U-M study comes at a time when poor air quality is becoming a significant area of concern in the US. While wildfires are quite common in the country, the record number of air quality alerts this year is mainly due to smoke from wildfires burning in Canada since May.

Microscopic toxins in air pollution, specifically fine particulate matter or PM2.5 (less than 2.5 microns in size) can enter the brain through the nose directly or cross the blood-brain barrier in other ways. PM2.5 is also known to affect the lungs, heart, and in emerging research, the brain and cognitive function.

Adar noted that many cities experienced more than 30 smoke-impacted days each year. Wildfires are thought to contribute up to 25% of fine particulate matter exposures over a year across the US and as much as 50% in some western regions of the country.

“While individual wildfires may be short-lived, these events are becoming more frequent in our communities due to warmer temperatures, drier conditions, and longer fire seasons. As we’ve seen, wildfire smoke can also travel very far distances,” Adar says.

Dementia is currently the seventh leading cause of death and one of the major causes of disability and dependency for older people, according to the World Health Organization.

The U-M findings are based on research into the development of dementia among nearly 30,000 adults from across the US over an 18-year period.

According to the study, air pollution from wildfire events is not just sending people with respiratory ailments to the hospitals but also results in longer lasting effects to the body. With the changing climate, it’s likely that these threats to health will increase.

Image source: University of Michigan

Branko Miletic

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