Air Pollution May Have an Effect on Cognitive Decline and Alzheimer Disease

Data reported at the Alzheimer Association International Congress (AAIC) show air quality improvements may be associated with slower rates of cognitive decline, greater clearance of amyloid from the brain, and lower risk of Alzheimer disease (AD). In these studies, air quality was typically measured as the amount of fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂)

In the US-based Women’s Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes (WHIMS-ECHO; NCT00745056), measures of air quality from 1996 through 2012 was correlated with women's cognitive functioning measured from 2008 through 2018. The women in the study were age 74 to 92 at enrollment. During the periods measured, overall air quality improved and mean cognitive function declined (as expected with aging). 

Over a median 6 years of follow up, the risk of dementia, which occurred in 18% (398/2239) of participants, was lower by 14% and 26%, respectively, in those with relatively higher and much higher air quality improvement stratified by quartile. Those living in areas with more improvement in air quality also had slower rates of cognitive decline equivalent to 1 year less progression. Cognitive decline was measured with Telephone Interview for Cognitive Status-modified (TICSm) and California Verbal Learning Test (CVLT). Notably, statistically significant correlations between lower rates decline in the cognitive domains of episodic memory, working memory, and attention with NO₂ level improvements but not PM_2.5 improvements. These correlations were independent of age, region, education, apolipoprotein E (ApoE) ε4 genotypes, and cardiovascular risk factors. 

“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. But, what’s exciting is we’re now seeing data showing that improving air quality may actually reduce the risk of dementia,” said Claire Sexton, DPhil, Alzheimer Association director of Scientific Programs and Outreach. “These data demonstrate the importance of policies and action by federal and local governments, and businesses, that address reducing air pollutants.”

A French-based 3-cohort study had similar results. Land-use modeling was used to estimate PM_2.5 levels and suggested improvement in air quality from 1990 to 2000. In 7,051 individuals assessed beginning 10 years later and lasting for 12 years of follow-up, risk of dementia decreased by 15% and the risk of AD decreased by 17% for every 1 mcg/m³ decrease in PM_2.5, independent of sociodemographic and health behaviors factors and APOE genotype. 

Lending further support to an association of air quality and dementia, the Ginko Evaluation of Memory Study followed 4 communities of adults age 75 or more at enrollment who did not have dementia at baseline. Plasma levels of amyloid β_1-40, a biomarker for dementia, were compared with air quality in the neighborhood where participants resided. Increase of PM₁₀ of 3 mcg/m³ and NO₂ 7 parts per billion both correlated with a 1.8% increase in amyloid β_1-40 plasma levels.