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expert reaction to longitudinal cohort study on exposure to fine particulate matter (PM2.5) and neurological disorders

Research, published in Lancet Planetary Health, looked at exposure to fine particulate matter (PM2.5) and neurological disorders.


Dr Sara Imarisio, Head of Research at Alzheimer’s Research UK, said:

“Air pollution is linked to many adverse health outcomes, with more and more evidence suggesting it increases our risk of developing dementia.

“Dementia is not an inevitable part of getting older, but factors including age, genetics, and the environment we live in all affect the risk of developing the condition. In this large study, researchers found higher levels of air pollution are linked with a greater number of likely dementia cases in the United States. While the researchers could not tell if the study participants had been exposed to a number other dementia risk factors, including whether or not they smoked, they were able to consider their socio-economic status and exposure to air pollution seemed to have an effect on top of this. This study also only picked up the more severe cases of dementia, with the true number of those developing dementia likely to be even higher.

“Observational studies such as this are useful for identifying potential risk factors but they cannot tell us about cause and effect. Diseases like Alzheimer’s start years before symptoms appear, and it would be helpful to know where the people who took part in the study lived in the decades before they developed dementia.”

“With one in three people born today expected to develop dementia in their lifetime, there is a pressing need to identify and understand potential risk factors for the condition. Good brain health should be a focus throughout life to reduce the risk of dementia and working towards cleaner air in our cities should remain a critical public health goal.”


Dr Beckie Port, Research Manager at Parkinson’s UK, said:    

“This research provides the most robust evidence to date that long term exposure to air pollutants may play a role in the deterioration of incurable conditions like Parkinson’s. 

“There is increasing evidence that air pollution is linked with both the occurrence and progression of such conditions. This US study highlights that there may be no safe level of exposure and that the greater the exposure, the greater the risk of adverse health effects.

“Parkinson’s is the fastest-growing neurological condition in the world and over time, it eats away at a person’s quality of life. By advancing our understanding of the role nature and the environment play, alongside numerous other genetic and lifestyle factors, we hope to gain insights that allow us to stop, slow or even prevent devastating conditions like Parkinson’s.” 


Fiona Carragher, Director of Research and Influencing at Alzheimer’s Society, said:

“Air pollution is a hot topic in dementia research. While this study adds to the evidence that air pollution could raise your dementia risk, we still need to know how particulate pollution might be causing changes in the brain, and if these lead to Alzheimer’s disease or other dementias.

“It’s also important to remember that this study only looked at people with dementia admitted to hospital and we can’t rule out the possibility of other factors being involved. As the number of people with dementia in the UK is set to rise to a million by 2025 it is critical the Government commits to doubling dementia research funding to allow researchers to urgently address these kinds of urgent questions.”


Prof Tara Spires-Jones, UK Dementia Research Institute Programme Lead and Deputy Director, Centre for Discovery Brain Sciences, University of Edinburgh, said:

“In this study, Shi and colleagues looked at data from over 63 million people and observed an association between estimated exposure to air pollution and hospital admissions for Alzheimer’s or Parkinson’s disease.  This study is robust since scientists examined data from a large number of people, but it is not possible with this type of observational study to determine whether the exposure to air pollution itself increased the risk of Alzheimer’s and Parkinson’s. It is possible that air pollution acts through damaging cardiovascular health, which is linked to risk of neurological diseases, but further studies are needed to understand the biology of this association.  We need more research to understand the brain changes caused by environmental risk factors for neurological diseases to develop life changing treatments or ways to prevent these diseases altogether.”


Dr Ivan Koychev, Senior Clinical Researcher, University of Oxford and Clinician Scientist at Dementias Platforms UK (DPUK),  said:

“This is a large study attempting to link air pollution as assessed by habitation in specific post codes in the US to risk for neurodegenerative diseases (Alzheimer’s and Parkinson’s disease).

“The study is notable for its large size and also, most significantly, for being able to demonstrate a linear relationship between the level of pollution and risk of being admitted with Alzheimer’s or Parkinson’s. The authors accounted for the main confounders that would be relevant (age, ethnicity, socio-economic status); it is notable that the reported effects were stronger for women, Caucasians (probably due to longer life expectancy in these groups) as well urban dwellers.

“The conclusions are limited by the study design being able to establish association between air pollution and neurodegenerative disease but not causation. While the specific link between air pollution and neurodegeneration needs further work, the report adds further evidence for long-term health implications of air pollution. Therefore, taken together with other recent publications the paper adds weight to conclusions that controlling air quality may improve public health outcomes.” 


Dr Stefan Reis, Head of Atmospheric Chemistry and Effects, UK Centre for Ecology and Hydrology (UKCEH), said:

“This study contributes to the growing body of evidence which suggests that exposure to air pollution even at comparatively low concentrations has widespread negative health effects.

“While respiratory and cardio-vascular diseases have been well known to be linked to air pollution, showing links between exposure to fine particulate matter and brain health in a comprehensive study highlights the importance to act swiftly in reducing  exposure, not only in hotspot areas.

“These findings are timely as they will inform the debate about adopting the World Health Organisation’s  guideline value for PM2.5 of 10 μg m-3, however the study indicates that negative health impacts occur even below this level. Based on these and similar findings, reducing exposure to PM2.5 in the whole population should become a key priority for air pollution control policies.”



Long-term effects of PM2·5 on neurological disorders in the American Medicare population: a longitudinal cohort study’ by Liuhua Shi et al. was published in Lancet Planetary Health at 23:30 UK time on Monday 19th October.



Declared interests

Prof Tara Spires-Jones: I have no conflicts of interest with the study.

Dr Ivan Koychev: No relevant COIs in this case apart from being funded by the MRC-funded Dementias Platform UK project.

Dr Stefan Reis: I have not been involved in this study and no interest to declare.

None others received.

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