Air Pollution May Lead to Alzheimer's Disease

Air pollution from power plants and motor vehicles may significantly increase the risk of dementia, especially among older women, according to a new study published by Translational Psychiatry.

Specifically, older women who inhabit areas where fine particulate matter exceeds EPA standards are at an 81% higher risk of cognitive decline, and have a 92% higher risk of developing dementia.

If these findings are confirmed in the general population, air pollution may be linked to 21% of dementia cases, according to the study.

“Microscopic particles generated by fossil fuels get into our body directly through the nose into the brain,” said study co-senior author Caleb Finch, PhD. “Cells in the brain treat these particles as invaders and react with inflammatory responses, which over the course of time, appear to exacerbate and promote Alzheimer’s disease.”

While it is known that air pollution can cause other adverse health effects, the researchers believe that it may impact the brain more than previously known.

“Although the link between air pollution and Alzheimer’s disease is a new scientific frontier, we now have evidence that air pollution, like tobacco, is dangerous to the aging brain,” Dr Finch said.

Women who had the APOE₄ gene seemed to be more at risk of developing dementia. This gene is known to increase the risk of Alzheimer’s disease, according to the study.

“Our study — the first of its kind conducted in the US — provides the inaugural scientific evidence of a critical Alzheimer’s risk gene possibly interacting with air particles to accelerate brain aging,” said study co-senior author Jiu-Chiuan Chen, MD, ScD. “The experimental data showed that exposure of mice to air particles collected on the edge of USC damaged neurons in the hippocampus, the memory center that is vulnerable to both brain aging and Alzheimer’s disease.”

This latest research adds to the numerous other findings that link PM 2.5 inhalable particles with the onset of dementia.

Included in the study were 3647 women, aged 65 to 79, who were included in the Women’s Health Initiative Memory Study. At baseline, none of the participants had dementia. Geographic location, race, education, socioeconomic status, lifestyle, and conditions were accounted for.

In a related animal study, the authors exposed APOE₄ gene-carrying female mice to the tiny air pollution particles for 15 weeks. Mice with this gene exposed to the particles were found to accumulate 60% more amyloid plaques, compared with the control group, according to the study. Accumulation of amyloid plaques is a marker of Alzheimer’s disease, as it causes cognitive decline.

“Our state-of-the-art aerosol technologies, called particle concentrators, essentially take the air of a typical urban area and convert it to the air of a freeway or a heavily polluted city like Beijing,” said study co-author Constantinos Sioutas, ScD. “We then use these samples to test exposure and assess adverse neuro-developmental or neuro-degenerative health effects.”

Since millions of people have dementia, these findings may provide a way to reduce disease burden.

“Our study has global implications as pollution knows no borders,” Dr Finch said.

Additional studies are needed to confirm this relationship, and determine how pollution enters and harms the brain. Pollution monitors will likely be important in doing this, according to the study.

However, less than one-third of countries currently have pollution monitors, which are critical for continuing the study of pollution on health.

“We analyzed data of high PM2.5 levels using standards the EPA set in 2012,” Dr Chen said. “We don’t know whether the lower PM2.5 levels of recent years have provided a safe margin for older Americans, especially those at risk for dementia.”

Due to increased regulations, the air has been cleaner recently, and this was associated with fewer cases of dementia, according to the study. These findings may lead to more stringent regulations to decrease dementia and other health conditions.

In further studies, the authors plan to evaluate how PM 2.5 impacts men, and how the pollutant interacts with cigarette smoke and other pollutants.

“Many studies have suggested that early life adversities may carry into later life and affect brain aging,” Dr Chen said. “If this is true, then maybe long-term exposure to air pollution that starts a downward spiral of neurodegenerative change in the brain could begin much earlier and rev up in later life.”