Air Quality and Dementia Risk

August 23, 2021

Improving air quality improves cognitive function and reduces dementia risk: accumulated evidence shows that reducing air pollution, especially fine particulate matter (PM2.5) and pollutants from the burning of fuel, is associated with lower risk of all-cause dementia and Alzheimer’s disease.

Several new studies reported at the “Alzheimer’s Association International Conference” (AAIC) 2021 – the world’s largest gathering of researchers from around the world focused on Alzheimer’s and other dementias which took place at the end of July in Denver and virtually – show that improving air quality may improve cognitive function and reduce dementia risk. While research has linked air quality and cognition previously, these new data at AAIC 2021 explore how air pollutants might impact dementia and what reducing them might mean for long-term brain health.

“We’ve known for some time that air pollution is bad for our brains and overall health, including a connection to amyloid buildup in the brain,” said Claire Sexton, DPhil, Alzheimer’s Association director of scientific programs and outreach. “But what’s exciting is we’re now seeing data showing that improving air quality may actually reduce the risk of dementia.”

According to the “Alzheimer’s Association” this is the first accumulated evidence that reducing air pollution, especially fine particulates and pollutants from the burning of fuel, is associated with lower risk of all-cause dementia and Alzheimer’s disease.

Among the key findings are:

1) Air Quality Improvement May Slow Cognitive Decline and Reduce Dementia Risk in Older U.S. Women

Reduction of fine particulate matter (PM2.5) and traffic-related pollutants (NO2) per 10% of the Environmental Protection Agency’s (EPA) current standard over 10 years was associated with 14% and 26% reductions in dementia risk, and slower cognitive decline, in older U.S. women. These benefits occurred in women regardless of their age, level of education, the geographic region where they lived and whether they had cardiovascular disease.

Although studies have found that improved air quality is associated with better respiratory health and longer life expectancy, it’s unknown if improved air quality can also improve brain health. To investigate this further, Xinhui Wang, Ph.D., University of Southern California, and colleagues investigated whether older women living in locations with greater reduction in air pollution may have slower decline in their cognitive function and be less likely to develop dementia.

Wang and team looked at a group of older women (aged 74-92) in the U.S. … who did not have dementia at the beginning of the study. Participants were followed from 2008-2018 and detailed cognitive function tests were done every year to determine whether they developed dementia. Participants’ home addresses were noted and mathematical models were used to estimate the air pollution levels at these locations over time. The researchers found that, in general, air quality greatly improved over the 10 years before the study began.

During a median of six years of follow-up, cognitive functions tended to decline as women aged, as expected. However, for those living in locations with greater reduction per 10% of the EPA’s current standard in both PM2.5 (fine particles that are 30 times thinner than a human hair) and NO2 (indicator of traffic-related pollutants), their risk of dementia decreased by 14% and 26%. “The possible benefits found in our studies extended across a variety of cognitive abilities, suggesting a positive impact on multiple underlying brain regions,” Wang said.

2) Reduction of Fine Particulates is Associated with Reduced Risk of Dementia in Older French Adults

Reduction of PM2.5 concentration over 10 years was associated with a reduced risk of all-cause dementia in French individuals by 15% and of Alzheimer’s disease by 17% for every microgram of gaseous pollutant per cubic meter of air (µg/m3) decrease in PM2.5.

Noemie Letellier, Ph.D., University of California, San Diego, and colleagues worked with the French Three-City Study, a large cohort of more than 7,000 participants aged 65 or older, to investigate the links between air pollution exposure and dementia risk.

The researchers observed reduction of PM2.5 concentration between 1990-2000, which was associated with a 15% reduced risk of all-cause dementia and a 17% reduced risk of Alzheimer’s disease for every microgram of gaseous pollutant per cubic meter of air (µg/m3) decrease in PM2.5, independent of socio-demographic and health behaviors factors, and APOE (Apolipoprotein E) genotype. “These data, for the first time, highlight the beneficial effects of reduced air pollution on the incidence of dementia in older adults.” Letellier said.

3) Long-Term Air Pollution is Associated with Increased Beta Amyloid Plaques

Long-term exposure to air pollutants was associated with higher beta amyloid levels in the blood in a large U.S. cohort, showing a possible biological connection between air quality and physical brain changes that define Alzheimer’s disease.

Accumulation of beta amyloid plaques is one of the hallmarks of Alzheimer’s disease. While a relationship between air pollution and increased beta amyloid production has been found in animal and human studies, relatively little is known about the effects of long-term exposure to air pollution on beta amyloid.

Christina Park, Department of Epidemiology at University of Washington, and colleagues examined associations between exposure to air pollutant levels of fine particulate matter (PM2.5), larger particles (PM10) and nitrogen dioxide (NO2), and levels of Aβ1-40 (one of the major protein components of plaques) in more than 3,000 individuals who were dementia-free at the beginning of the Ginkgo Evaluation of Memory Study. The study evaluated and averaged air pollution levels at participant residential addresses for time periods up to 20 years prior to taking blood tests to measure individuals’ beta amyloid.

People who were in the study longer (eight years) showed a strong link between all three air pollutants and Aβ1-40. These are some of the first human data suggesting long-term exposure to air pollutants is associated with higher Aβ1-40 levels in the blood. “Our findings suggest that air pollution may be an important factor in the development of dementia,” Park said. “Many other factors that impact dementia are not changeable, but reductions in exposure to air pollution may be associated with a lower risk of dementia.”

Press Release by the AAIC-Alzheimer’s Association International Conference 2021