In contrast, exposure to environmental pollutants such as fine particulate matter, nitrogen dioxide or soot significantly increases the risk of ischaemic stroke

Living near green spaces reduces the risk of suffering a stroke by 16%

photo_camera PHOTO/LA CAIXA - From left to right, the authors of the study: Rosa Vivanco, Jaume Roquer, Sergio Olmos, Uxue Lazcano, Carla Avellaneda and Cathryn Tonne.

The risk of suffering an ischaemic stroke, the most common type of stroke, is reduced by 16% in people who have green areas within 300 metres of their homes. This is revealed in a joint study by the Hospital del Mar Medical Research Institute, the Hospital del Mar, the Catalan Health Quality and Assessment Agency (AQuAS) of the Catalan Government's Department of Health and the Barcelona Institute for Global Health (ISGlobal), a centre promoted by the "la Caixa" Foundation. This is the most important work in this field done so far in Europe, analysing data from the entire population of Catalonia between 2016 and 2017. It is published in the journal Environment International.

The study has taken into account information on exposure to three air pollutants linked to vehicle traffic, from more than three and a half million people selected from among the 7.5 million residents in Catalonia, those over 18 years old who had not suffered a stroke before the start of the work. Specifically, it analysed the impact of the levels of particulate matter below 2.5 microns (PM2.5), nitrogen dioxide (NO2) and soot particles in the place of residence of each of the people studied. The number and density of green spaces within a 300-metre radius of their homes was also analysed. These data were obtained after georeferencing them and designing models of exposure to the two determinants, using population data obtained by reusing health information generated in Catalonia and anonymised by the Data Analytics Programme for Health Research and Innovation (PADRIS), which is managed by the Catalan Agency for Health Quality and Assessment (AQuAS).

More pollution, more risk of stroke

The results indicate a direct relationship between the increase in NO2 concentration levels in the atmosphere and the risk of suffering an ischaemic stroke. For every increase of 10 micrograms (µg) per cubic metre, this risk increases by 4%. The same happens when PM2.5 levels increase by 5 µg/m3. And in the case of soot particles, the risk increases by 5% for every 1 µg/m3 increase in the atmosphere. These figures are the same for the whole population, regardless of other socio-economic factors, age or tobacco addiction.

"It should be borne in mind that, unlike other air pollutants, which have different sources, NO2 is mainly caused by road traffic. Therefore, if we really want to reduce the multiple risks this pollutant poses to people's health, we need to implement bold measures to reduce car use," says Cathryn Tonne, researcher at ISGlobal.

"The study demonstrates the importance of environmental determinants in stroke risk. Given that the prediction is that the incidence, mortality and disability attributed to the disease will increase in the coming years, it is important to know all the risk factors involved", explains Dr. Carla Avellaneda, a researcher in the Neurovascular Research Group at IMIM-Hospital del Mar and one of the main authors of the study. Previous studies by the same group had already provided evidence on the relationship of factors such as soot or noise levels on the risk of suffering a stroke or its severity. All these factors act as triggers for stroke.

In contrast, having an abundance of green spaces within the same radius as the home has a direct impact on reducing the risk of stroke. Specifically, up to 16%. In this sense, "people who live surrounded by a higher degree of greenery in their place of residence are protected against the onset of stroke," says Dr Avellaneda. In general, exposure to green spaces is considered to have beneficial effects through different mechanisms, such as stress reduction, increased physical activity and social contacts, and even exposure to an enriched microbiome.

Rethinking the established limits for atmospheric pollutants

In view of these data, the researchers point out that the current levels of atmospheric pollution considered safe need to be reconsidered. At present, the thresholds set by the European Union are 40 µg/m3 for NO2, which the World Health Organisation reduces to 10 µg/m3, and 25 µg/m3 for PM2.5, which the WHO limits to 5 µg/m3. There are no established levels for soot particles. In fact, the levels recorded during the period analysed were, on average, lower than those set by the European authorities (17 µg/m3 for PM2.5, 35 µg/m3 for NO2 and 2.28 µg/m3 for soot).

"Despite the fact that the levels set by the European Union are met, we are faced with the paradox that there is still a risk to health, as we have found in this study, where there is a direct relationship between exposure to pollutants in our environment and the risk of suffering a stroke," explains Dr. Rosa María Vivanco, lead author of the study and researcher at AQuAS and IMIM-Hospital del Mar. "The danger still exists and many more measures need to be taken," she adds, taking into account the increase in the urban population and its ageing.

In this sense, Dr. Jaume Roquer, head of the Neurology Service at Hospital del Mar and coordinator of the Neurovascular Research Group at IMIM-Hospital del Mar, points out that "this study demonstrates the real impact that environmental aspects have on the health of the population of Catalonia. In view of the effects of atmospheric pollution, the lack of green spaces, noise, etc., more efforts and strategies are needed to reduce their impact on the population. Its harmful effect is permanently and globally damaging. We have to fight to achieve more sustainable towns and cities where living does not mean assuming an increased risk of illness".

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