Air pollution linked to risk of hospital admission with dementia

A study of over 63 million people in the United States finds that air pollution exposure increases hospital admission risk for neurological conditions, including Alzheimer’s disease and other dementias.

The burden of neurodegenerative disease is rising. According to estimates from Harvard’s NeuroDiscovery Center, in 30 years, more than 12 million people in the U. S. will receive a diagnosis for neurodegenerative disease.

The progressive loss of neurons causes neurodegenerative diseases, including Alzheimer’s disease, the most common form of dementia, and Parkinson’s disease.

Although increasing rates of these conditions are partly due to an aging population, the way we live may also be increasing their likelihood.

The National Institute of Environmental Health Sciences (NIEHS), for example, fund a range of research to investigate what these factors might be, including exposure to pesticides, toxic metals, such as lead, and air pollution.

Air pollution, in particular, seems to have a strong connection with neurological disease. A landmark study in 2016 found that magnetite — a potentially toxic particle in polluted air — was able to get into human brain tissue.

A further study found a significant association between residential air pollution and receiving a diagnosis with dementia in London, United Kingdom. More recently, scientists have shown that even young people exposed to air pollution show markers of neurodegenerative disease.

New research led by Harvard T. H. Chan School of Public Health adds to the evidence on this, finding that levels of fine particulate matter — tiny particles with a diameter of 2.5 micrometers or under — in the air have associations with hospitalization for neurodegenerative disease in a U.S. cohort.

The study, published in The Lancet‘s Planetary Health journal, uses the largest ever dataset to assess the link between air pollution and neurological disorders.

The study

The study, which is the first nationwide cohort study to look at the association between fine particulate air pollution and neurodegenerative disease in the U.S., uses data from over 63 million people. Everybody in the study was a Medicare-fee-for-service beneficiary over the age of 65.

The researchers investigated the connection between long-term exposure to fine particulate matter and hospital admissions with a diagnosis of Parkinson’s disease or Alzheimer’s disease and related dementias.

The researchers estimated air pollution exposure by zip code and based hospital admissions information on almost 17 years’ worth of data spanning 2000–2016.

Strong association

The researchers found a significant association between exposure to air pollution and hospitalization for neurodegenerative disease.

The risk of hospital admission for Parkinson’s disease or Alzheimer’s disease and related dementias significantly increased with rising levels of fine particulate matter — even at levels below current “safe” standards in the U.S.

Specifically, for every 5 micrograms per cubic meter of air increase in annual fine particulate matter concentrations, there was a 13% increased risk for hospital admissions.

“Our study builds on the small but emerging evidence base indicating that long-term [fine particulate matter] exposures are linked to an increased risk of neurological health deterioration,” says co-lead author of the study Xiao Wu, a doctoral student at Harvard Chan School.

Policy change needed?

The risk was greater for some sections of the population than others. For example, women, white people, and people living in urban areas were at the greatest risk of hospitalization.

Although people living in urban areas are more likely to experience exposure to high air pollution levels, the researchers say the greater risks among white people and women could be due to the longer life expectancy in these groups.

For Parkinson’s disease, the greatest risk of hospital admission was among older adults in the northeastern U.S., while for Alzheimer’s disease and related dementias, the risk was greatest for older adults in the Midwest.

Researchers explain that air pollutants might increase neurodegeneration risk because some air pollutants (including fine particulate matter) cross the blood-brain barrier into the brain, where they could have toxic effects.

For example, pollutant particles could trigger the inflammatory processes in the brain associated with Alzheimer’s disease.

Based on their findings, the researchers call for policy change. They say lowering the maximum permitted levels of ambient fine particulate matter could have significant health benefits for the aging U.S. population.

“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 [fine particulate] concentrations and improve air quality overall.”

– Co-senior author Antonella Zanobetti

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