Study Ties Long-term Exposure to Air Pollution to Parkinson’s Mortality

Research in Europe augments growing evidence linking air pollution and Parkinson’s

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Long-term exposure to air pollutants such as fine particulate matter (PM2.5), nitric dioxide, and black carbon increases the risk of dying from Parkinson’s disease, according to a study of more than 200,000 adults from six European countries.

Notably, these associations were observed even for pollutant levels below current European Union (EU) air quality standards, “suggesting that there are no lower threshold levels below which air pollution is not harmful,” the researchers wrote.

These findings add to the increasing body of evidence pointing to a link between air pollution and Parkinson’s.

The study, “Long-term air pollution exposure and Parkinson’s Disease mortality in a large pooled European cohort: an ELAPSE study,” was published in the journal Environment International.

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Parkinson’s is believed to be caused by a number of genetic and environmental factors working in combination. Mounting evidence shows that breathing polluted air may put people at increased risk of developing the neurodegenerative disease.

Air pollutants include gases and particulate matter, or microscopic solids or liquid droplets. Pollutant gases include nitrogen dioxide and black carbon, which are derived mostly from the burning of fossil fuel, and ozone, which results from pollutants emitted from cars, power plants, refineries, and chemical plants.

PM2.5 are particles less than 2.5 micrometers in diameter — about 30 times smaller than a strand of human hair — abd consisting of smoke, aerosols, soot, mold spores, dander, and the like.

Some of these air pollutants are so tiny they can go deep into the lungs and enter the bloodstream. They have been suggested to enter the brain by breaching the blood-brain barrier, a highly selective membrane that prevents potentially harmful agents in circulation from reaching the brain and the spinal cord.

Once in the brain, it is thought that air pollutants may trigger inflammation and damage nerve cells, which may contribute to the development of neurodegenerative diseases such as Parkinson’s.

However, there is limited evidence about the impact of long-term exposure to air pollution with respect to death from Parkinson’s.

The ELAPSE project

With this in mind, a team of researchers in Europe evaluated the potential links between long-term exposure to PM2.5, nitrogen dioxide, black carbon, and ozone, as well as eight PM2.5 components, and Parkinson’s mortality as part of the ELAPSE project.

ELAPSE is a Europe-wide collaborative initiative looking at the effects of low air pollution levels on health outcomes. Low levels are defined using cut-points defined by current EU limit values, U.S. standards, and World Health Organization (WHO) guidelines.

ELAPSE previously has associated long-term exposure to low air pollution levels with a higher frequency of cardiovascular diseases, adult-onset asthma, lung diseases, and certain types of cancer, as well as higher mortality from neurological and psychiatric disorders.

In the current study, the researchers analyzed pooled data from ELAPSE’s seven datasets, or cohorts, of six European countries: France, Germany (two datasets), the Netherlands, Austria, Denmark, and Sweden.

Mortality classifications

Parkinson’s mortality was assessed through the number of deaths whose cause was reported to be Parkinson’s, secondary (atypical) parkinsonism, or Parkinson’s-associated dementia.

A total of 271,720 adults were included in the final analyses. Their mean age at cohort entry was 47.1 years, ranging from 42.1 in the Austrian cohort to 72.9 years in a Swedish sub-cohort. More than two-thirds (69%) were women, 22% were current smokers, and 41% were overweight.

Over a mean follow-up period of 19.7 years, 381 of these adults (0.14%) died due to Parkinson’s: 380 from Parkinson’s disease and one due to secondary parkinsonism.

When the team looked at exposure to outdoor air pollutants in 2010, they found that it varied across cohorts, with people in Denmark and Sweden being exposed to the lowest levels of PM2.5 and black carbon.

Also, almost all participants were exposed to annual PM2.5 levels that were well below the EU limit — 25 micrograms per cubic meter (mcg/m3) — but above the U.S. limit (12 mcg/m3) and the new WHO guidelines (5 mcg/m3).

The same stood for nitrogen dioxide, with exposure levels being below the EU limit (40 mcg/m3) but above the new WHO guidelines (10 mcg/m3). The levels of ozone exposure also were above WHO guidelines.

“Comparing with 2010 exposure levels, the concentrations of PM2.5 were much higher at baseline [study’s start], with smaller differences observed for the other pollutants,” the team wrote.

After adjusting for potential influencing factors, long-term exposure to higher PM2.5 levels was significantly associated with a 25% higher risk of death from Parkinson’s.

Body weight may be a factor

This link was particularly stronger among participants who were not overweight, “which may be indicative of [Parkinson’s disease-related] weight loss with progressive disease stages due to malnutrition,” the researchers wrote.

Among the eight PM2.5 components, potassium was the only component whose greater exposure was associated significantly with a higher Parkinson’s mortality risk.

Long-term exposure to higher levels of nitrogen dioxide or black carbon also tended to be associated with an increased risk of dying from Parkinson’s, but this failed to reach statistical significance.

Higher ozone exposure was linked significantly to a lower mortality risk (by 26% , which is not consistent with previous reports.

This may be due to the observed association between higher levels of ozone and lower levels of the other three pollutants, “the small exposure contrasts within each sub-cohort, or generally low levels of [ozone] exposure in our study,” the team wrote.

Notably, regarding PM2.5, nitrogen dioxide, and black carbon exposure levels, the researchers found no evidence of a lower threshold below which air pollution was not linked to a higher risk of death from Parkinson’s.

These findings highlight that “long-term exposure to PM2.5, [nitrogen dioxide] and [black carbon] were associated with the risk of dying from PD [Parkinson’s disease], with PM2.5 found to be the most relevant pollutant for this risk,” the researchers wrote.

“We also found that associations persisted at low levels of pollutant concentration, well below current EU air quality standards,” the team wrote, adding “strong novel evidence in support of an association between air pollution and PD.”

Among the study’s limitations, the team noted that a diagnosis of Parkinson’s may not have been available for all individuals at the time of death, and lack of information on the time spent outdoors, and commuting to work, as well as other sources of air pollution.

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