The Connections between Air pollution and Brain Disease

The proof is becoming too much to ignore.

We typically write about current air quality news or interesting, relevant air quality news, no matter how old.  Currently, there is a barrage of studies coming out that show how air pollution affects our brains; it’s all negative, and it the “A” word (Alzheimer’s Disease, AD) is mentioned frequently.  If you personally know how devastating an AD or dementia diagnosis is, you know how important it is that we discover and avoid the causes of these brain diseases.

The most broad study was a meta-analysis of existing scientific literature to examine the link between air pollution and dementia.  In 2025, researchers at the University of Cambridge reviewed 51 studies, at the end including 34 relevant papers and data from more than 29 million participants.  They found a positive and statistically-significant association between three types of air pollutant and dementia (Is the air you breathe silently fueling dementia? A 29-million-person study says yes):

• PM2.5: For every 10 micrograms per cubic meter (μg/m³) of PM2.5, an individual's relative risk of dementia would increase by 17%. (The average roadside measurement for PM2.5 in Central London in 2023 was 10 μg/m³.)

• NOx: For every 10 μg/m3 of NO2, the relative risk increased by 3%. (The average roadside measurement for NO2 in Central London in 2023 was 33 µg/m³.)

• Soot (mostly from vehicle exhaust and burning wood). For each 1 μg/m³ of soot as found in PM2.5, the relative risk increased by 13%. (annual mean soot concentrations measured at select roadside locations in 2023 were 0.93 μg/m³ in London).

Therefore, for example, some Londoners would have a 17 + 9 + 13, or 39% higher risk of dementia from these 3 pollutants!  Air pollution is thought to trigger inflammation and oxidative stress in the brain, through direct entry to the brain or via the same mechanisms underlying lung and cardiovascular diseases. Both oxidative stress and inflammation play a well-established role in the onset and progression of dementia.

The other concerning part of this study was that the majority of people included in the meta-analysis were white and living in high-income countries, even though marginalized groups tend to have a higher exposure to air pollution, meaning that their risk for dementia is probably even greater.  The analysis also showed the pollution effect seemed stronger for vascular dementia, a type of dementia caused by reduced blood flow to the brain. than for AD.  

Furthermore, if you or a loved one is already diagnosed with AD, it would be best to get to the cleanest air possible, as soon as possible. Another 2025 study showed that exposure to high concentrations of air pollution may worsen AD by accelerating the buildup of toxic proteins in the brain and speeding up cognitive decline.  Post-mortem tissue from people with AD revealed that those who lived in areas with higher concentrations of fine particulate matter in the air even just one year had more severe accumulation of amyloid plaques and tau tangles -- hallmarks of AD pathology -- compared to those with less exposure. These individuals also experienced faster cognitive and functional decline, including memory loss, impaired judgment, and difficulty with personal care. (Smog in the brain: Dirty air speeds Alzheimer’s decline)

The researchers determined the rate of cognitive decline by using data from satellites and local air quality monitors to model the amount of PM2.5 in the air based on where each of 600 people with AD lived. They found that for every increase of 1 microgram per cubic meter of PM2.5, the risk for worse AD amyloid and tau buildup increased by 19 percent. Moreover, the clinical records of these individuals revealed that those who lived in areas with high concentrations of PM2.5 with advanced disease also had greater cognitive impairment and more rapid onset of symptoms, including memory loss, difficulty with speech, and diminished judgement, compared to people who lived in areas with lower concentrations of air pollution.

If you’re reviewing your mental agility even as you read this article…another study showed that air pollution, even for brief exposures, can cause “brain fog”, making it difficult to concentrate and complete everyday tasks and behave in a socially acceptable manner.  (Ahhh, of course there’s a reason for that last blow-up!)  The same mechanisms of inflammation and oxidative stress triggered by PM2.5 can affect us in the short term by reducing selective attention and emotion recognition.  Selective attention is the ability to focus on the task at hand and make good decisions, such as prioritizing items on your shopping list in the supermarket, while ignoring other products and resisting impulse buys.  Emotion recognition involves detecting and interpreting emotions in yourself and others, helping to guide socially acceptable behavior.  In the working world, reductions in these two areas translate to productivity loss and even safety issues as even small lapses in concentration can be dangerous for some workers, equipment operators or drivers. (Air pollution clouds the mind and makes everyday tasks challenging)

When exposed to air pollution, there is a chemical change in the brain called S-nitrosylation, which prevents brain cells from making new connections and ultimately, results in death of the cells.  A team of researchers at Scripps Research in California discovered how S-nitrosylation occurs with a specific protein in the brain, CRTC1, which helps regulate genes that are critical for learning and long-term memory.  When excess Nitric Oxide (NO) is present from air pollution or wildfire smoke, it binds to the sulfur atom(s) in the protein, and prevents CRTC1 from binding to another critical brain regulatory protein, failing to stimulate other genes necessary for forming connections between neurons (making memories). 

The team observed high levels of S-nitrosylated CRTC1 at an early stage of disease in Alzheimer's mouse models and in human neurons derived from stem cells of Alzheimer's patients, which supports the idea that the chemical change plays a key role in the development of disease symptoms.  They developed a way of preventing S-nitrosylation by genetically modifying CRTC1, removing the sulfur-containing amino acid (called cysteine) required for the chemical reaction, so that the memory-related functions were restored.  They hope to target new drugs that are able to block the S-nitrosylation in the brain, because, even without exposure to vehicle exhaust and wildfire smoke, older brains naturally produce more NO.  (How air pollution and wildfire smoke may contribute to memory loss in Alzheimer's disease)

Finally, a study in the UK that spanned 10 years and 1,127 adults over 65 years old showed that individuals residing in areas with the highest levels of NO₂ and PM2.5 performed worse on cognitive tests compared to those living in areas with average pollution levels. The most compelling evidence of association was observed in language skills, with individuals in the most polluted areas scoring in the bottom third of the cognitive tests performed. (Exposure to air pollution may harm brain health of older adults)

These five studies, all published within one year, point to one thing: air pollution has a direct effect on our brain function or dysfunction.  Check out our article highlighting wildfire smoke’s other effects on immunity, infants, men’s fertility and more, and another on the effect of a child’s air quality on their physical and mental development.

It’s ironic that human intellect is getting choked with the byproduct of the rise of Artificial Intelligence (AI).  Data centers that are being built and expanded at breakneck speed to fuel AI searches come at a cost: air and water pollution, often in minority neighborhoods.  (AI might be “saving” us time and money, but at what air quality cost?)

It’s come to this: as we learn more about what is causing dementia and Alzheimer’s disease, some people should focus on adding air purifiers and/or masks to their environment, more than cross-word puzzles and “brain-health supplements”.  If you are living in a polluted-air region, no matter your age, it’s best to look for ways to mitigate your air quality or move to a less-polluted area if possible.  Your brain is too essential to put at risk by breathing PM2.5 and NOx!

Photo by Max Bender on Unsplash