Smog-filled towns and cities have been linked to increased risks for Alzheimer's and suicide among children and young adults.
A University of Montana researcher, Lilian Calderon-Garcidueñas, and her collaborators studied 203 autopsies of Mexico City residents ranging in age from 11 months to 40 years.
Metropolitan Mexico City is home to 24 million people exposed daily to concentrations of fine particulate matter and ozone above U.S. Environmental Protection Agency standards. The researchers tracked two abnormal proteins that indicate development of Alzheimer's, and they detected the early stages of the disease in babies less than a year old.
"Alzheimer's disease hallmarks start in childhood in polluted environments, and we must implement effective preventative measures early," said Calderon-Garcidueñas. "It is useless to take reactive actions decades later."
The scientists found heightened levels of the two abnormal proteins - hyperphosphorylated tau and beta amyloid - in the brains of young urbanites with lifetime exposures to fine-particulate-matter pollution (PM2.5). They also tracked Apolipoprotein E (APOE 4), a well-known genetic risk factor for Alzheimer's, as well as lifetime cumulative exposure to unhealthy levels of PM2.5 - particles which are at least 30 times smaller than the diameter of a human hair and frequently cause the haze over urban areas.
Findings indicated that Alzheimer's starts in early childhood, and the disease progression relates to age, APOE 4 status and particulate exposure. Researchers found hallmarks of the disease among 99.5 percent of the subjects they examined in Mexico City. In addition, APOE 4 carriers had a higher risk of rapid progression of Alzheimer's and 4.92 higher odds of committing suicide versus APOE 3 carriers, controlling for age and particulate exposure.
The authors concluded that ambient air pollution is a key modifiable risk for millions of people across the globe, including millions of Americans who are exposed to harmful particulate pollution levels.
The research is published in the Journal of Environmental Research.
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