Every year 15 million people suffer a stroke, of which five million die and another five million suffer a lifelong disability due to its consequences, according to the World Health Organization (WHO). Hypertension and smoking are two of the main risk factors for suffering a stroke, along with diseases associated with aging, but there are also environmental factors that influence its appearance.
Breathing polluted air is one of them, but its short-term harmful effects have been less studied. Now, a review of 110 observational studies that include 18,035,408 cases of ischemic stroke – which occurs when an artery in the brain is blocked – has revealed that there is a strong connection between recent exposure to environmental pollution and the occurrence of this accident. cerebrovascular disease, and that certain toxic substances present in the air we breathe also increase the risk of suffering from this health problem.
The meta-analysis has been carried out by researchers from the University of Jordan in Amman who have studied the data from these 110 works in which the cases of patients in Asia (58.8% of the studies), Europe (24.6% %) and America (16.7%), focusing on the five days prior to the vascular accident. Their findings have been published in the journal Neurology.
“Environmental particles such as carbon monoxide, sulfur dioxide, or ozone increase the risk of suffering an ischemic stroke and dying from the stroke, even with short-term exposure”
“This close temporal association underlines the importance of implementing global initiatives to develop policies to reduce air pollution. By doing so, the burden of ischemic stroke and its consequences will be alleviated,” the authors highlighted in the article.
Toxic substances present in the air we breathe
The researchers analyzed pollutants such as nitrogen dioxide, ozone, carbon monoxide and sulfur dioxide, as well as different particle sizes, including PM1 – which is air pollution less than 1 micron (μm) in diameter. , as well as PM2.5 and PM10. PM2.5 or smaller includes inhalable particles that come from motor vehicle emissions, fuel burning by industrial activities, or forest fires, while PM10 includes dust from roads and construction sites.
“It has been observed that smaller particles, such as those of 2.5 micrometers, are associated with a greater risk of ischemic stroke than larger particles, such as those of 10 micrometers,” explains the main author, Ahmad, in statements to SINC. Toubasi, from the University of Jordan.
Regarding the risks associated with each chemical compound for cerebrovascular diseases, the scientist affirms that “some are more harmful than others”, but that, in general terms, the risk “ranges between 5% due to an increase of one part per thousand million ozone and 28% due to the increase of one part per billion of nitrogen dioxide.”
And he adds that the results of his analysis showed that in the risk of suffering a stroke “the highest concentrations of nitrogen dioxide were associated with an increase of 28%; ozone levels were related to a 5% increase; carbon monoxide, with 26%, and sulfur dioxide, 15%.”
Different chemical compounds and different levels of air pollution were also linked to a higher incidence of stroke mortality. The highest concentrations of nitrogen dioxide had a 33% greater impact on the risk of death from stroke, and sulfur dioxide had a 60% greater impact. Regarding the size of harmful particles present in the air, those that are connected with the numbers of deaths from strokes are, according to the analysis, PM2.5 with 9%, and PM10, with 2%.
Ahmad Toubasi explained to SINC that “the majority of the studies included in our analysis were carried out in high-income countries, while the data available from low- and middle-income countries was limited,” and that “no research work was included.” Africa or the Middle East, despite the fact that these regions have high levels of air pollution and bear a significant burden of morbidity and mortality from stroke.” This also highlights the urgency of adopting measures to reduce the levels of air pollution to which the population is exposed.
Francisco Moniche, Section Head of the Stroke Unit in the Neurology Service of the Virgen del Rocio University Hospital – Institute of Biomedicine of Seville (IBiS) has acknowledged in statements to SMC Spain that “the analysis shows that different environmental particles such as monoxide carbon (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3), as well as particles of different sizes increase the risk of suffering an ischemic stroke and the possibility of dying from the stroke , even in short-term exposure to this contamination (less than 5 days).”
According to this expert, although other studies had already established a relationship between continuous exposure to environmental pollution and an increased risk of stroke (both ischemic and hemorrhagic) and heart disease, “until now there were no conclusive data about short-term exposure and the relationship with the risk of stroke.” As a limitation, it stands out “that it is based on observational studies, so other causes could coexist for these findings such as socioeconomic level, access to the health system, diet, exercise, etc.”
For her part, Elena López-Cancio, member of the Department of Neurology, Stroke Unit of the Central University Hospital of Asturias (HUCA) and associate professor of Health Sciences at the University of Oviedo, also speaking to SMC Spain, points out that “without a doubt these Results are very relevant to establish policies that are aimed at reducing environmental pollution. In the latest update of the stroke prevention guides of the Spanish Society of Neurology (2021), a specific section on environmental pollution was established, recommending, based on the existing evidence at the time, applying public health policies that allow reducing air pollution due to its potential effect on stroke prevention.”
