The smog could also poison the brain. US scientists have discovered that people most exposed to atmospheric pollution from PM2.5 dust have a greater probability of having high quantities of Alzheimer's 'signal' amyloid plaques in the brain. The study – published in 'Neurology', the official journal of the American Academy of Neurology – it does not prove that smog causes the neurodegenerative disease, but indicates an association that needs to be explored further, the researchers point out. “These findings add evidence that fine particulate matter from traffic-related air pollution influences the amount of amyloid plaques in the brain. Further studies are needed to investigate the mechanisms underlying this link,” says Anke Huels of Emory University of Atlanta, author of the work.
The scientists examined the brain tissue of 224 people with an average age of 76, mostly residents of the Atlanta metropolitan area, who agreed to donate their brains after death to contribute to dementia research. For each of them, based on their home address at the time of death, the researchers analyzed exposure to traffic smog: the average level of exposure to air pollution was 1.32 micrograms per cubic meter (μg/ m3) in the year before death and 1.35 µg/m3 in the previous 3 years. The authors then compared exposure to smog with the presence of brain signs of Alzheimer's, such as amyloid plaques and tau protein tangles. They observed that people most exposed to air pollution one and three years before death were more likely to have higher levels of amyloid plaques in their brains. More precisely, those who had been exposed to PM2.5 levels above 1 µg/m3 in the year before death had an almost double probability of having more cerebral amyloid plaques, while those most exposed to smog in the 3 years before dying had an 87% higher chance of having more plaques.
The scientists also wondered whether the main genetic variant associated with Alzheimer's, Apoe e4, had any effect on the relationship between smog and brain indicators of the disease. The analysis showed a stronger relationship between air pollution and signs of Alzheimer's in the brains of people without the Apoe e4 variant. “This suggests – explains Huels – that environmental factors such as smog could contribute to Alzheimer's in patients whose disease cannot be explained by genetics.”
There are two main limitations of the study: on the one hand, exposure to air pollution was measured only based on the address of residence at the time of death, which may have led to an incorrect classification of the exposure itself; on the other hand, the observations mainly concerned white people with a high level of education, therefore the results may not be representative of other populations. Hence the need, highlighted by the authors, to go deeper with new research to shed light on the smog-Alzheimer link.
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