The air that we breathe: could air pollution put us at risk of stroke?

For those of us who live in the city, it can often be difficult to avoid gaseous fumes and pollutants – they’re all around us. But could they put us at a greater health risk than previously thought?

According to a study published in The BMJ this week, air pollution is linked to a higher risk of stroke, particularly in developing countries. A second article found a link between air pollution and 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.

A team of researchers from Edinburgh University reviewed studied that 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. It was found that there is 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.

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. Higher concentrations of gaseous pollutants were measured in low to middle income countries when compared to high-income countries. These results show that there needs to be a change, and soon.

So how does air pollution cause a stroke? Prior research showed that air pollution can affect the cells that line the circulatory system and increase activity of the sympathetic nervous system, which can lead to narrow blood vessels, an increase in blood pressure, the restriction blood supply to tissues and increase the risk of thrombosis.

And then there’s the new study that has shown a link between air pollution and anxiety. Researchers at The Johns Hopkins and Harvard Universities conducted studies of over 71,000 women aged between 57 and 85 years old.

Anxiety is the most common psychiatric disorder and affects around 16 per cent of the world’s people at some point in life.

Scientist assessed exposure to particulate matter in the participant’s location over five periods (one month, three months, six months, one year and 15 years) before assessment of anxiety via a self-rated quiz.

Distance from residence address to the nearest major road, a common indicator for traffic related air pollution exposure, was also analysed.

The findings showed that around 15 per cent of women experienced high anxiety symptoms and exposure to particulate matter was linked to a higher risk of anxiety. While fine particles in the air were found to have a significant association with anxiety, there wasn’t a link to coarse particles. And those women who lived 50 to 200m from a major road were more likely to have higher anxiety symptoms than those living more than 200m away.

Michael Brauer from the University of British Columbia, Canada, wrote that these studies “confirm the urgent need to manage air pollution globally as a cause of ill health” and that reducing “air pollution could be a cost effective way to reduce the large burden of disease from both stroke and poor mental health”.

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