[News release] Air pollution linked to increased risk of anxiety and stroke
Remember, correlation does not mean cause! See also the rebuttal below
Air pollution is linked to a higher risk of stroke, particularly in developing countries, finds a study published in The BMJ today. In a second article, new research also shows that air pollution is associated with anxiety.
Stroke is a leading cause of death and kills around 5 million people each year worldwide. Common risk factors include obesity, smoking and high blood pressure. But the effect of the environment, such as, air pollution is uncertain because evidence is lacking.
In a systematic review and meta analysis, a team of researchers from Edinburgh University looked at the association between short term air pollution exposure and stroke related hospital admissions and deaths. In total, they analysed 103 observational studies that covered 28 countries across the world.
Gaseous pollutants included in the analysis were carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone. In addition, particulate matter was included: PM 2.5 (fine particles less than 2.5 µm in size) and PM 10 (coarse particles less than 10 µm in size).
Results showed an association between carbon monoxide (1.5% increased risk per 1 ppm), sulphur dioxide (1.9% per 10 ppb) and nitrogen dioxide (1.4% per 10 ppb) and stroke related hospital admissions or death. The weakest association was found for ozone.
Both PM 2.5 and PM 10 were associated with hospital admissions or deaths due to stroke, by 1.1% and 0.3% per 10 µg/m3 increment respectively. The first day of air pollution exposure was found to have the strongest association.
Low- to middle-income countries experienced the strongest associations compared to high-income countries. Only 20% of analysed studies were from low- to middle-income countries – mostly mainland China – despite these countries having the highest burden of stroke.
Both studies were observational and no definitive conclusions can be drawn about cause and effect, and the teams of researchers call for more research.
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