Study links long-term pollution exposure to Alzheimer’s, Parkinson’s, and additional neurological disorders

Researchers from the Emory Rollins School of Public Health have discovered a significant association between air pollution and hospital admission for various neurological disorders, including Alzheimer’s disease, Parkinson’s disease, and other disorders, based on a long-term study led by Rollins and Harvard University of more than 63 million U.S. adults aged 65 and over. The study’s findings are published online in The Lancet Planetary Health.  

Liuhua Shi, ScD, research assistant professor in the Gangarosa Department of Environmental Health, is lead author of the study. “Our study is the first attempt to associate neurological disorders and fine particulate matter in a nationwide epidemiology study,” says Shi. “It indicates that the current standards are not protecting the aging American population enough.”

Researchers looked at hospital admissions data from 63,038,019 Medicare recipients in the U.S. between 2000-2016 and compared that with estimated air pollution concentrations by zip code. They found that, for each 5 microgram per cubic meter of air (μg/m3) increase in annual fine particulate matter (PM_2.5) concentrations, there was a 13 percent increased risk for first-time hospital admissions both for Parkinson’s disease and for Alzheimer’s disease and related dementias. 

The increased risk was found even below supposedly safe levels of PM_2.5 exposure, which, according to current U.S. Environmental Protection Agency standards, is an average of 12 μg/m3 or less over the course of a year. This suggests that there is no such thing as a “safe” threshold for pollution exposure.

The study found that women, white people, and urban populations were particularly susceptible to Parkinson’s and Alzheimer’s diagnoses. The highest risk for first-time Parkinson’s disease hospital admissions was among elderly in the northeastern U.S. First-time Alzheimer’s related hospital admissions were at highest risk among elderly in the Midwest.

While past studies have shown links between PM_2.5 exposure and cardiovascular disease, respiratory illness, and premature mortality, this is the first nationwide analysis of the link between long-term PM_2.5 exposures and neurodegenerative diseases in the U.S.

Neurological disorders are the second leading group cause of death at a global level. As the population continues to age, the immediate need for addressing risk factors, such as environmental exposures, should be a top research priority. This research emphasizes the urgent need for improving overall air quality to reduce PM_2.5 exposure to less than current national standards.