Brain Shrinkage, Memory Problems, Depression Linked to Air Pollution Chemicals

Two separate scientific studies have revealed some sobering news about the link between air pollution chemicals and serious brain harm.  In the first study, higher exposures to air pollution chemicals were associated with increased depressive symptoms and subsequent memory decline. In the second study, people who had higher levels of air pollution exposure had more brain shrinkage–the kind of shrinkage commonly seen in people suffering from Alzheimer’s disease.

Depression and Air Pollution Chemicals

Depression is a serious condition in the U.S. and uncovering some of the potential root causes is critical.  Fortunately, in addition to previous studies linking synthetic chemicals found in highly processed food to depression, science may have uncovered yet another one of the triggers: air pollution chemicals.  In the study of women aged 80 years and older who were living in locations with higher exposures to air pollution, this exposure was associated with increased depressive symptoms.  Additionally, while we already know that late-life exposures to ambient air pollutants accelerate brain aging and increase dementia risk, the present study results suggested that depressive symptoms might play a role in linking long-term air pollution exposure to memory decline more than 10 years after the exposure.

“This is the first study showing how air pollution exposures affect depressive symptoms as well as the interrelationship between the symptoms and subsequent memory decline that had not been found in older people aged less than 80 years.”  -Andrew Petkus, PhD.,  lead researcher


Brain Shrinkage and Air Pollution Chemicals

Brain atrophy has also been linked to the chemicals in air pollution.  The results of the second study suggest that older women who live in locations with higher levels of air pollution may have more brain shrinkage (the kind seen in Alzheimer’s disease), than women who live in locations with lower levels of air pollution. This study looked at fine particle pollution* and found that breathing in high levels of this kind of air pollution was linked to shrinkage in the areas of the brain vulnerable to Alzheimer’s disease.

Study overview (S

The study involved 712 women with an average age of 78 who did not have dementia at the start of the study. Participants provided health histories as well as information on race/ethnicity, education, employment, alcohol use, smoking and physical activity. All women received MRI brain scans at the start of the study and five years later.

Researchers used the residential addresses of each participant to determine their average exposures to air pollution** in the three years before the first MRI scan. They then divided participants into four equal groups. The lowest group was exposed to an average of 7 to 10 micrograms of fine particle pollution per cubic meter of air (µg/m3). The highest group was exposed to an average of 13 to 19 µg/m3. The U.S. Environmental Pollution [sic] Agency (EPA) considers average yearly exposures up to 12 µg/m3 to be safe.

Researchers then used a machine learning tool to measure signs of Alzheimer’s disease in the brain, a tool that had been trained to identify patterns of brain shrinkage specific to an increased risk of Alzheimer’s disease by reading the brain scans of people with the disease.

Participants’ MRI brain scans at the start of the study and five years later were assigned scores based on how similar they were to Alzheimer’s disease patterns identified by the machine learning tool, specifically brain changes in regions found to be vulnerable to Alzheimer’s disease. Scores ranged from zero to one, with higher scores showing more brain changes. Overall, the women’s scores changed from 0.28 at the start of the study to 0.44 five years later.

*Fine particle pollution consists of microscopic particles of chemicals, smoke, dust and other pollutants suspended in the air. They are no larger than 2.5 micrometers, 30 times smaller than the width of a human hair.

**Researchers examined only regional fine particle pollution, not other sources of pollution such as traffic emissions. 

Study results overview

For each 3 µg/m3 increase in air pollution exposure levels, researchers found a broader range of scores between the two scans and an average increase of 0.03, showing a greater extent of brain shrinkage over five years, which was equivalent to a 24% increased risk of Alzheimer’s disease. The increases remained the same even after adjusting for age, education, employment, cardiovascular disease, high blood pressure, physical activity and other factors that could affect brain shrinkage.

Conclusion: Late-life exposure to air pollution (PM2.5) is associated with increased neuroanatomical risk of Alzheimer’s Disease, which may not be explained by available indicators of cerebrovascular damage.

Journal Reference (1):  Andrew J. Petkus, Diana Younan, Xinhui Wang, Daniel P. Beavers, Mark A. Espeland, Margaret Gatz, Tara L. Gruenewald, Joel D. Kaufman, Helena C. Chui, JoAnn E. Manson, Susan M. Resnick, Gregory A. Wellenius, Eric A. Whitsel, Keith Widaman, Jiu‐Chiuan Chen. Air Pollution and the Dynamic Association Between Depressive Symptoms and Memory in Oldest‐Old Women. Journal of the American Geriatrics Society, 2020; Summary/ DOI: 10.1111/jgs.16889

Journal Reference (2): Younan, D., et al.  PM2.5 associated with gray matter atrophy reflecting increased Alzheimers risk in older women, Neurology Journal,