The Voice of Epidemiology


    Web EpiMonitor

► Home ► About ► News ► Job Bank Events ► Resources ► Contact

Numerous Studies Point to Neurotoxic Effects of Air Pollution

In a recent article, Science highlights the growing body of evidence suggesting that inhalation of fine and ultrafine particles commonly found in air pollution can damage the brain and increase the risk of developing dementia and Alzheimer’s disease. The potential for cognitive impairments is added to the long list of established health issues attributable to air quality such as asthma, lung cancer and heart disease.

Air Pollution and Dementia
One paper cited in the article and published last month in Translational Psychiatry was an 11-year epidemiological study of the effects of particulate matter (PM) exposure on women. The class of PM they studied is PM2.5, specifically particles with an aerodynamic radius less than 2.5μm. According to Arian Saffari, an author on the study that came out of the University of Southern California, “The smaller the particles that cells are exposed to, the higher their levels of oxidative stress.” Ultimately, the study found that “... airborne PM exposure promotes pathological brain aging in older women, with potentially a greater impact in ε4 carriers.” The authors “estimate that ~21% of accelerated cognitive decline and all-cause dementia are attributable to residential exposure to high ambient PM2.5.” The second finding is particularly interesting because Apolipoprotein E (APOE) ε4 is among the loci implicated in Alzheimer’s disease (AD) and yet these genetic alterations have so far accounted for less than half of AD cases. The present finding suggests the need for synergy between genetic and environmental factors to increase risk.

Another study referenced in the article was published last month in the Lancet. Based on existing evidence that living in closer proximity to a major roadway might have negative effects on cognition, a team from the University of Toronto set out to investigate more closely the associations between proximity to roadways and Parkinson’s disease, dementia and multiple sclerosis. Their finding? “In this large population-based cohort, living close to heavy traffic was associated with a higher incidence of dementia, but not with Parkinson's disease or multiple sclerosis.” Interestingly, persons living in less than 50 meters from a major road showed a 7% increased risk of developing dementia. That risk disappeared completely for individuals living greater than 200 meters from a major road. For those living in major cities at less than 50 meters from a major road, their risk increased to 12%.

Relating Animal Model Insights to Humans
Many of the other studies linking pollution exposure to damage in the brain have used animal models and translation to meaningful insights for humans is still necessary. The Science article notes this will be difficult as long-term data on pollution are lacking globally. Some work has been done to date however such as a review of 18 studies in 6 countries, including the US and China, where all but one showed correlation between dementia and high exposure to a component of air pollution.  More work needs to be done, however. And it’s clear that more data are necessary. Only a third of US counties monitor pollution and PM2.5 has only been monitored since 1997.

Using Simulation to Fill in the Missing Pieces
One solution to the lack of data may be simulation, and one study underway in Seattle will use modeling data to estimate lifetime exposures to PM2.5 allowing for correlations with dementia incidence. Participants in the study have already been monitored for cognitive changes for 20 years. All that’s missing is the PM2.5 data. Lianne Sheppard, a biostatistician at the University of Washington, says that combining the data set with genetic studies will allow their research group to understand “not just the epidemiology of the relationship between air pollution and cognition, but start drilling down to mechanisms” for interactions between pollutants and the brain.

Differing Impacts Across Socioeconomic Groups
On a final note, the Science article highlights the differential effects across socioeconomic groups. Because they more commonly live in areas with higher PM2.5 levels, the poor will be disproportionately affected. Additionally, recent studies have demonstrated a synergistic effect between pollution levels and other environmental stresses like litter and crime. This means that policy changes might be most effective if focused specifically on the most vulnerable communities. In the end, air pollution may end up an even bigger villain than originally predicted. According to Caleb Finch, a neuroscientist who works with the USC team, “I think [air pollution] will turn out to be just the same as tobacco - there’s no safe threshold.”

Science News Article

Translational Psychiatry Article

Lancet Article             ■

Reader Comments:
Have a thought or comment on this story ?  Fill out the information below and we'll post it on this page once it's been reviewed by our editors.

  Name:        Phone:   



      ©  2011 The Epidemiology Monitor

Privacy  Terms of Use  Sitemap

Digital Smart Tools, LLC