Francisco Moniche
Head of Section of the Stroke Unit in the Neurology Service of the Hospital Universitario Virgen del Rocio - Institute of Biomedicine of Seville (IBiS)
The present study performs a meta-analysis (an analysis combining data from multiple previous studies) on more than 18 million stroke patients demonstrating an association between recent exposure to environmental pollution and the risk of ischaemic stroke and its mortality. Ischaemic stroke is the most common type of stroke (80-85% of all strokes) and is caused by a lack of cerebral blood flow due to occlusion or thrombosis of a cerebral artery.
The analysis shows that different environmental particles such as carbon monoxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) as well as particles of different sizes increase the risk of ischaemic stroke and the likelihood of death from stroke, even in short-term exposure to this pollution (less than 5 days).
The data obtained are robust as they evaluate data from different studies with a large number of stroke patients (18 million) in multiple countries in Asia, Europe and America.
Several studies have previously shown that continuous exposure to air pollution increases the risk of stroke (both ischaemic and haemorrhagic) and heart disease but, until now, there was no conclusive data on short-term exposure and the relationship with stroke risk.
One limitation of the work is that it is based on observational studies, so there could be other causes for these findings, such as socioeconomic status, access to the health system, diet, exercise, etc. On the other hand, there seems to be a publication bias of positive studies that find an association between pollution and stroke. However, the large number of patients studied from multiple countries and different studies provides robust data for the study and its conclusions.