Neurological health has deteriorated due to climate change and air pollution, a literature review has suggested.
In a review that spanned 3 decades of research, temperature extremes and variability were linked to strokes, hospitalization for dementia and exacerbation of multiple sclerosis (MS), reported Andrew Dhawan, MD, DPhil, of the Cleveland Clinic, and colleagues.
Exposure to air pollutants, especially fine particulate matter (PM2.5) and nitrates – were linked to incidence and severity of stroke, headache, risk of dementia and exacerbation of MS, they added.
Moreover, favorable conditions for zoonotic diseases extend beyond traditional boundaries, providing opportunities for neuroinfectious diseases in new populations, the researchers wrote in Neurology.
“As the effects of climate change become increasingly apparent, we need to understand its impact on our patients and the conditions we treat as healthcare professionals,” Dhawan said. MedPage today. “This is the first large-scale study to summarize what is already known about climate change as it relates to neurological conditions.”
“We provide three key priorities for further study in our work – the effects of temperature and temperature variability on neurological conditions, changes in neuro-infectious diseases, and understanding how air pollutants affect the nervous system – which could provide a roadmap for future studies,” he said.
The international community aims to reduce global temperature rise to less than 1.5C by 2100, but irreversible environmental changes have already happened and will continue, Dhawan noted.
“In addition to understanding the magnitude of the problem, neurologists need to be aware of how the work they do might change,” he added. “It will be different depending on where they practice and the types of patients they see.”
The review looked at studies on the environment and neurological diseases in adults published between 1990 and 2022. The researchers identified 364 relevant papers: 289 on pollution, 38 on extreme weather events and temperature fluctuations, and 37 on neuroinfectious diseases. Most of the searches came from Asia (149), North America (105) and Europe (93).
A total of 24 studies assessed climate and the incidence of ischemic stroke, with evidence suggesting an increased risk of stroke at extreme temperatures. Six studies showed that the incidence of ischemic stroke increased with increasing temperature and relative humidity. Two studies showed an increase in stroke admissions at lower temperatures, “possibly because cold temperatures induce vasoconstriction and increase blood viscosity,” Dhawan and colleagues noted.
Two studies looked at hospital admissions and weather related to dementia; one showed that an average increase in temperature of 1.5°C increased the risk of hospitalization for dementia by 12%. Three studies linked seizure frequency to weather changes, four identified exacerbation of MS symptoms and two looked at headaches. One study showed that a 5°C increase in temperature increased the relative risk of headache ER visits.
Neuro-infectious diseases and climate
Neuro-infectious diseases were linked to climate change in 11 studies on West Nile virus, 13 on tick-borne encephalitis, six on meningococcal meningitis, five on Japanese encephalitis virus, one on viral meningitis unspecified and one on coccidioidomycosis. Several reviews have examined the effect of extreme weather conditions such as flooding on mosquito and rodent-borne diseases.
Predictive modeling of West Nile virus incidence in North America has suggested that conditions conducive to the virus may increase in the southern United States due to higher temperatures, lower precipitation, longer mosquito seasons long and more droughts. In addition, periods of transmission of tick-borne encephalitis are expected to lengthen in Europe and a new focus on Scandinavia may emerge, based on analyzes of epidemiological data between 1969 and 2018.
A total of 166 studies looked at stroke and air pollution. “Long-term and short-term exposures to air pollutants had substantial support for the association with ischemic stroke incidence and mortality,” observed Dhawan and colleagues. A global burden of disease analysis concluded that 9% of disability-adjusted life years and 8.5% of stroke deaths can be attributed to PM2.5 exposure, they noted. Air pollution was also linked to intracerebral hemorrhage.
Air pollutants were linked to dementia in 51 studies. Overall, 6.1% of incident dementia cases were estimated to be attributable to PM2.5 and nitrogen dioxide (NO2) exposure.
PM exposure and the incidence of Parkinson’s disease were examined in 19 papers and showed varying associations for each pollutant. “NOPE2 exposure has been examined in seven additional studies and its impact remains controversial,” Dhawan and colleagues noted.
Three studies have linked the incidence of ALS to exposure to air pollutants with varying results. Fourteen studies looked at headaches and pollution; the largest showed an association between a higher frequency of migraine-specific urgent care visits and higher average annual PM2.5 and no2 levels in California. Among 19 MS studies, short-term exposure to air pollutants was generally associated with exacerbations of disease activity.
“Climate change poses many challenges to humanity, some of which are not well studied,” Dhawan said. “For example, our review found no papers related to the neurological health effects of food and water insecurity, but these are clearly linked to neurological health and climate change.”
Most of the studies were conducted in resource-rich regions of the world, “suggesting a mismatch between where research is occurring and where changes are most acute,” the researchers acknowledged.
Dhawan and his co-authors have disclosed no relationship with the industry.