The University of Montana neuropathologist, Lilian Calderón-Garcidueñas, had been studying the brains as part of her research on environmental effects on neural development, and this particular set of samples came from autopsy examinations carried out on people who had died suddenly in Mexico City, where she used to work as a researcher and physician. When Lilian Calderón-Garcidueñas discovered abundant hallmarks of Alzheimer’s disease in a batch of human brain samples a few years ago, she initially wasn’t sure what to make of it. Although Calderón-Garcidueñas had collected much of the tissue herself while attending the autopsies in Mexico, the light-microscope slides she was analyzing had been prepared by her colleagues, so she was in the dark about what patient each sample came from. By the end of the project, she’d identified accumulations of the Alzheimer’s disease–associated proteins amyloid-ß and hyperphosphorylated tau in almost all of the 203 brains she studied. The people whose brains she’d been studying were not only adults, but teens and even children. For the last three decades, she’d been studying the health effects of Mexico City’s notoriously polluted air—a blight that earned the capital the dubious distinction of most polluted megacity on the planet from the United Nations in 1992. During that time, she’s discovered many links between exposure to air pollution and signs of neural damage in animals and humans. Although her findings are observational, and the pathology of proteins such as amyloid-ß is not fully understood, Calderón-Garcidueñas argues that air pollution is the most likely culprit behind the development of the abnormalities she saw in her postmortem samples—plus many other detrimental changes to the brains of Mexico City’s residents.
Once controversial, the theory that air pollution damages the brain is gaining traction in the research community. Although government officials in Mexico have worked to improve air quality since the 1990s, the last couple of years have seen thick smog descend over buildings, forcing periodic school and office closures to stop people from venturing into the toxic air. And it’s not just Mexico. As the rest of the world’s urban areas and their associated congestion continue to expand, most countries are witnessing increases in airborne contaminants, from noxious gases such as nitrogen oxides and ozone to fine particulate matter such as dust, soot, and nanospheres of metals that penetrate deep into the human body. One 2018 report by the Boston-based nonprofit Health Effects Institute warned that up to 95 percent of the people on Earth were breathing unsafe air. These trends are matched by an increasing incidence of respiratory and cardiovascular problems—consequences of the inflammation and tissue damage provoked by multiple components of air pollution. At the World Health Organization’s inaugural conference on air pollution last fall, health officials gathered to discuss data showing that dirty air is implicated in more than 7 million deaths per year. Only in the last few years, however, have researchers begun raising the alarm about links between humans’ exposure to air pollution and brain function.
Epidemiologists, psychologists, and neuroscientists are now working to fill in the gaps in knowledge of how air pollution might contribute to these less visible effects on human health, both by documenting the cognitive changes occurring in human populations exposed to air pollution, and by looking inside human and animal brains to try to decipher the underlying mechanisms. “This is the beginnings of a whole new field,” says Caleb Finch, a gerontologist at the University of Southern California (USC). “This is like tobacco research and cancer 70 years ago.”
Smog over Mexico City
Original published by Scientist Magazine