As the air people breathe gets dirtier, their odds for serious neurological disorders such as Parkinson's disease, Alzheimer's and other dementias rises, new research shows.
The long-term study of more than 63 million older Americans can't prove cause and effect, but does show a strong association between air pollution and brain disorders. The researchers said the link was seen even at levels of fine particulate (PM2.5) pollution that are deemed safe by the U.S. Environmental Protection Agency.
"Our study builds on the small but emerging evidence base indicating that long-term PM2.5 exposures are linked to an increased risk of neurological health deterioration, even at PM2.5 concentrations well below the current national standards," researcher Xiao Wu, a doctoral student in biostatistics at Harvard T.H. Chan School of Public Health in Boston, said in a school news release.
Dr. Alessandro Di Rocco directs the Movement Disorders Program at Northwell Health in Great Neck, N.Y. He wasn't involved in the new study, but said the findings aren't surprising.
"Over the past few years there has been growing evidence that environmental exposure to chemical substances, including pesticides and air pollution, may cause or facilitate the biological changes leading to neurodegeneration," said Di Rocco.
In the new study, Wu's team looked at data on hospital admissions in 2000 to 2016 from more than 63 million Medicare patients. The researchers linked these with estimated PM2.5 concentrations by the ZIP code where each patient lived.
The investigators found that for each 5 microgram per cubic meter increase in annual PM2.5 concentrations, there was a 13% greater risk for hospital admissions for Parkinson's disease, Alzheimer's disease and other dementias.
Women, white people and urban dwellers were particularly susceptible, the researchers noted.
The highest risk for Parkinson's disease was among older adults living in the Northeast, while those in the Midwest showed the strongest risk for Alzheimer's and other dementias.
The bottom line, according to co-researcher Antonella Zanobetti: "Our U.S.-wide study shows that the current standards are not protecting the aging American population enough, highlighting the need for stricter standards and policies that help further reduce PM2.5 concentrations and improve air quality overall." Zanobetti is a principal research scientist in the Harvard Chan School's department of environmental health.
For his part, Di Rocco said the new study is "unique in its scope and size, demonstrating a strong nationwide correlation between degree of air pollution and risk for neurological disorders of aging."
He believes that the rise in neurodegenerative disease among Americans can't be explained by age alone. That means that "identifying air pollution as an important environmental risk factor can lead to a public health intervention that may diminish over time the occurrence of these neurological disorders," Di Rocco said.
The report was published online Oct. 19 in the journal The Lancet Planetary Health.
For more on air pollution and health, head to the Environmental Defense Fund.