Scientific American May 2020 pp42-47 “The Role of Air Pollution” “Airborne particles spewed by car exhausts and other sources are now strongly linked to Alzheimer’s. Recent research shows how they can travel from the lungs and nose to the brain”.
Research has shown that the incidence of Alzheimer’s Disease increases with long term exposure to air pollution whether measured by nitrogen dioxide or particulate matter known as PM 2.5 (PM2.5 refers to atmospheric particulate matter [PM] with a diameter of less than 2.5 micrometers, which is about 3% the diameter of human hair. They can only be detected by an electron microscope. Source blissair.com).
Simply put, what damages the lung and heart damages the brain. Controlled studies in mice and findings in dogs and humans living in highly polluted cities show brain plaques even in infants, children, and adults. There is a strong correlation of air pollution with neurodegenerative disease. So, air pollution has become a hot topic in AD.
Epigenetic factors including air pollution contribute significant risk for late-onset AD. PM2.5 produced by burning fossil fuels is inhaled deep into the lungs where it passes quickly into the circulation and then across the blood brain barrier (BBB). PM2.5 also bypasses the BBB entering directly through the olfactory nerve and into the olfactory bulb of the brain. Risk of AD has a strong correlation with PM2.5 exposure.
Living close to a major highway increases risk by 12% versus living further away (50 meters vs. 200 meters from the roadway). Metals in PM2.5 may be especially neurotoxic triggering cytokine release, inflammation and nerve death. P2.5 particles may also carry microbial toxins like lipopolysaccharide (LPS) from bacteria. LPS stimulates the innate immune system leading also to inflammation etc.
Chronic exposure matters but likely most people succumb to cardiovascular disease before having clear signs and symptoms of neurodegenerative disease. An early precursor of AD is a decline in episodic memory (episodic memory contains memories about events from one’s own past, e.g., how I fed rabbits in childhood, how I have been to New York, the first kiss, how I cooked spaghetti yesterday-source Tutor2u.net)
What to do?
Reduce risk by decreasing exposure to air pollution, exercise as this reduces risk in part by improving cardiovascular output and in part by increasing the production of BDNF from muscle. Higher blood flow improves brain oxygen levels and Brain-Derived Neurotrophic Factor improves nerve growth and nerve function.