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Environmental factors worsen neurologic health – US review of 30 years’ research

Climate change, airborne pollution and temperature extremes are all playing major roles in changing infectious disease conditions, while increasing risks of serious illnesses, a scoping literature review has suggested.

The review that spanned 30 years of research of temperature extremes and variability showed links with stroke, dementia hospitalisation and multiple sclerosis (MS) exacerbation, reported Dr Andrew Dhawan, DPhil, of the Cleveland Clinic, and colleagues.

Additionally, they added that exposure to air pollutants, especially fine particulate matter (PM2.5) and nitrates, was tied to stroke incidence and severity, headache, dementia risk, and MS exacerbation.

Moreover, favourable conditions for zoonotic diseases are expanding beyond traditional borders, presenting opportunities for neuro-infectious disease in new populations, the researchers wrote in Neurology.

“As the effects of climate change become increasingly apparent, we need to understand how it impacts our patients and the conditions we treat as healthcare professionals,” Dhawan told MedPage Today. “This is the first wide-scale study to summarise what is already known about climate change as it pertains to neurological conditions.

“We provide three key priorities for further study in our work – the effects of temperature and variability in temperature on neurological conditions, changes in neuro-infectious diseases, and understanding how airborne pollutants affect the nervous system – which might provide a roadmap for future studies,” he said.

The international community aims to reduce global temperature rise to under 1.5°C before 2100, but irreversible environmental changes already have occurred and will continue, Dhawan noted.

“Apart from understanding the scale of the issue, neurologists need to be aware of how the work they do might change,” he added. “This will be different depending on where they practice and what types of patients they see.”

The review examined studies about environment and neurologic disease in adults published between 1990 and 2022. The researchers identified 364 relevant papers: 289 about pollution, 38 about extreme weather events and temperature fluctuations, and 37 about neuro-infectious diseases. Most research was from Asia (149), North America (105), and Europe (93).

Temperature changes

A total of 24 studies evaluated climate and ischaemic stroke incidence, with evidence suggesting rising stroke risk at temperature extremes. Six studies showed ischaemic stroke incidence rose with increasing temperature and relative humidity increases. Two studies showed increased stroke admissions at lower temperatures, “perhaps because cold temperatures induce vasoconstriction and increase blood viscosity”, they noted.

Two studies examined dementia-related hospital admissions and weather; one showed that mean temperature increases of 1.5ºC raised the risk of dementia hospitalisation by 12%. Three studies related seizure frequency to meteorological changes, four identified MS symptom exacerbation, and two looked at headache. One study showed that a temperature increase of 5ºC raised the relative risk of headache visits to the emergency department.

Neuro-infectious diseases and climate

Neuro-infectious diseases were related to climate change in 11 studies about West Nile virus, 13 about tick-borne encephalitis, six about meningococcal meningitis, five about Japanese encephalitis virus, one about unspecified viral meningitis, and one about coccidioidomycosis. Several reviews examined the effect of extreme weather like floods on mosquito- and rodent-borne diseases.

Predictive modelling of West Nile virus incidence in North America suggested suitable conditions for the virus could increase in the southern US due to higher temperatures, lower rainfall, longer mosquito seasons, and more droughts. In addition, transmission periods for tick-borne encephalitis were expected to lengthen in Europe and a new focus on Scandinavia may emerge, based on analyses of epidemiological data from 1969-2018.

Airborne pollutants

Overall, 166 studies looked at stroke and air pollution. “Long- and short-term exposures to airborne pollutants had substantial support for association with ischaemic stroke incidence and mortality,” Dhawan and colleagues observed.

A global burden of disease analysis concluded that 9% of stroke disability-adjusted life years and 8.5% of stroke deaths could be attributed to PM2.5 exposure, they said. Airborne pollution also was linked with intracerebral haemorrhage.

Airborne pollutants were related to dementia in 51 studies. Overall, 6.1% of incident dementia cases were estimated as attributable to PM2.5 and nitrogen
dioxide (NO2) exposure.

Particulate matter exposure and Parkinson's incidence was examined in 19 papers and showed varying associations for each pollutant. “NO2 exposure was examined in seven additional studies and its impact remains controversial,” the researchers said.

Three studies related ALS incidence to air pollutant exposure with varying results. Fourteen studies examined headaches and pollution; the largest one showed an association between higher frequency of migraine-specific urgent care visits and elevated average annual PM2.5 and NO2 levels in California.

Among 19 MS studies, short-term exposure to airborne pollutants was generally associated with exacerbations of disease activity.

“Climate change poses many challenges for humanity, some of which are not well-studied,” Dhawan said. “For example, our review did not find any articles related to effects on neurologic health from food and water insecurity, yet these are clearly linked to neurologic health and climate change.”

Most studies were conducted in resource-rich regions of the world, “suggesting a discordance between where research occurs and where changes are most acute”, the researchers acknowledged.

Study details

Impacts of Climate Change and Air Pollution on Neurologic Health, Disease, and Practice: A Scoping Review

Shreya Louis, Alise Carlson, Abhilash Suresh, Joshua Rim, MaryAnn Mays, Daniel Ontaneda, Andrew Dhawan.

Published in Neurology on 16 November 2022


Background and objectives
Although the international community collectively seeks to reduce global temperature rise to under 1.5ºC before 2100, irreversible environmental changes have already occurred, and as the planet warms these changes will continue to occur. As we witness the effects of a warming planet on human health, it is imperative that neurologists anticipate how the epidemiology and incidence of neurologic disease may change. In this review, we organised our analysis around three key themes related to climate change and neurologic health: extreme weather events and temperature fluctuations, emerging neuro-infectious diseases, and pollutant impacts. Across each of these themes, we appraised and reviewed recent literature relevant to neurological disease and practice.

Studies were identified using search terms relating to climate change, pollutants, and neurologic disease in PubMed, OVID MEDLINE, Embase, PsycInfo, and grey literature. Studies published between 1990 and 2022 were included if they pertained to human incidence or prevalence of disease, were in English, and were relevant to neurologic disease.

We identified a total of 364 articles, grouped into the three key themes of our study; extreme weather events and temperature fluctuations (38 studies), emerging neuro-infectious diseases (37 studies), and pollutant impacts (289 studies). The included studies highlighted the relationships between neurologic symptom exacerbation and temperature variability, tick-borne infections and warming climates, and airborne pollutants and cerebrovascular disease incidence and severity.

Temperature extremes and variability both associated with stroke incidence and severity, migraine headaches, hospitalisation in dementia patients, and multiple sclerosis exacerbations. Exposure to airborne pollutants, especially PM2.5 and nitrates, associated with stroke incidence and severity, headaches, dementia risk, Parkinson’s disease, and MS exacerbation. Climate change has demonstrably expanded favourable conditions for zoonotic diseases beyond traditional borders, and poses the risk of disease in new, susceptible populations. Articles were biased towards resource-rich regions, suggesting a discordance between where research occurs and where changes are most acute. As such, three key priorities emerged for further study; neuro-infectious disease risk mitigation, understanding the pathophysiology of airborne pollutants on the nervous system, and methods to improve delivery of neurologic care in the face of climate-related disruptions.


Neurology article – Impacts of Climate Change and Air Pollution on Neurologic Health, Disease, and Practice: A Scoping Review (Open access)


Medpage Today article – Neurologic Health Is Worse Due to Environmental Factors, Review Suggests (Open access)


See more from MedicalBrief archives:


One in six people dying prematurely from air pollution


Significant link between environmental pollution and neuro-psychiatric disorders


Air pollution’s tiny particles may trigger non-fatal heart attacks


Even low levels of air pollution linked to heart damage




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