Hong Kong Baptist University study finds strong association between PM2.5 and neurological disorders

HONG KONG SAR – Media OutReach – 6 September
2021 – A comprehensive, systematic meta-analysis conducted by HKBU scientists
found a significant association between exposure
to PM_2.5, i.e., fine particulates with equivalent diameters of less
than 2.5 microns suspended in the air, and neurological disorders. These include
stroke, dementia, Alzheimer’s disease, Parkinson’s disease and autism spectrum
disorder (ASD). Neurological disorders are the leading cause of disability
and the second leading cause of death worldwide, posing serious challenges to
global health.

 

Professor
Ken Yung Kin-lam (right) and Dr Fu Pengfei, Postdoctoral Research Fellow of the
Department of Biology of HKBU, find a strong association between PM_2.5
and a wide range of neurological disorders

The paper with the study’s
finding was published in the academic journal Science of the Total Environment, and
has become the top 1% highly-cited paper
worldwide by citation in the field of Environment and Ecology, according to
Essential Science Indicators (ESI).

Comprehensive study covers 26 countries or regions

 

As systematic reviews and
meta-analyses on the association between PM_2.5 exposure and
neurological disorders have been limited so far, the HKBU research team, led by
Professor Ken Yung Kin-lam, Professor of
the Department of Biology of the University, analysed a total of 1,645
articles published by June 2018, and identified 80 eligible studies that covered
a population of more than 6.33 million from 26 countries or regions in all
continents except Antarctica.

 

Previous meta-analyses of a similar
nature covered at most seven countries, and nearly all of them were lightly
polluted. In contrast, HKBU’s study covered countries and regions known to have
more serious air pollution problems, such as Chile, China and India.

 

PM_2.5 exposure increases stroke risks

 

After a series of statistical analyses
of the data published in the selected studies, the research team used odds
ratio (OR) to represent the association between PM_2.5 exposure and
the risk of different neurological disorders. Odds ratio, commonly used in
public health analysis, is a measure of association between an exposure and an
outcome. An odds ratio value of 1 indicates that an exposure does not affect
odds of an outcome; a value of over 1 means an exposure is associated with
higher odds of an outcome.

 

Analysis results of the
association between PM_2.5 exposure and stroke risks are tabulated as
below:

 

PM2.5 exposure	Risk of stroke (in odds ratio)	Risk of stroke mortality (in odds ratio)
Short-term	1.01	1.02
Long-term	1.14	1.15
Lightly polluted areas	1.01	1.06
Heavily polluted areas	1.02	Data not available

 

The results revealed that exposure to PM_2.5 in general increases
the risks of stroke and stroke mortality, with the risk associated with long-term
exposure more significant than with short-term exposure. It also showed
that the risk of stroke in heavily
polluted areas is higher than that in lightly polluted areas.

 

Neurological disorders strongly associated with PM_2.5
exposure

 

Analysis results of the
association between PM_2.5 exposure and the risks of developing other
neurological disorders are presented as below:

 

Neurological disorders	Risk (in odds ratio)
Alzheimer’s disease	3.26
ASD	1.68
Parkinson’s disease	1.34
Dementia	1.16

 

The results revealed that PM_2.5 exposure is strongly
associated with increased risks of Alzheimer’s disease, ASD, Parkinson’s
disease and dementia.

 

PM_2.5 is typically
made up of heavy metals, organic carbon and polycyclic aromatic hydrocarbons
suspended in the air. According to studies, some of the tiny particles and
soluble components can enter the bloodstream by many pathways, such as crossing
the blood-brain barrier and gaining access to the central nervous system. These
particles can induce inflammation, death of cells and DNA damage.

 

Call to improve air quality for public health’s sake

 

“While various hypotheses were
suggested on the underlying mechanisms of how PM_2.5 causes different
types of neurological disorders, it remains an area with many unknowns for
biomedical scientists to explore. More vigorous research endeavours are
required before we can fully understand the mechanisms, based on which we can
formulate effective environmental and public health strategies in response,” said
Professor Yung.

 

Tomorrow (7 September) will be
the 2nd International Day of Clean Air for blue
skies designated by the United Nations General Assembly, with the theme
“Healthy Air, Healthy Planet”, which
emphasises the health effects of air pollution.

 

“The International Day of
Clean Air for blue skies reminds us of the urgency for national governments and
the international community to collaborate and take swift, effective actions to
improve air quality, given its extensive health implications. Our study made it
clear that PM_2.5 exposure, a typical indicator of air pollution, is closely
associated with many neurological disorders, and thus improving air quality
will be a direct response to this public health challenge,” said Professor Yung.