Air pollution raises our risk of a stroke and its later complications

Exceeding the World Health Organization’s recommended air pollution exposure limit could substantially increase our risk of a first-time stroke

By Jason Arunn Murugesu

Consistent exposure to air pollution may raise our risk of a first-time stroke

Martyn Williams/Alamy

Living in a highly polluted area may raise the risk of a stroke and its subsequent complications.

Air pollution has been linked to strokes before. Hualiang Lin at Sun Yat-sen University in China and his colleagues wanted to understand the risk among people with no history of stroke. They were also interested in how air pollution may influence any post-stroke complications, such as cardiovascular disease.

The team assessed the air pollution exposure of more than 318,000 people living in the UK. This was based on air pollution monitoring carried out by separate researchers between January 2010 and 2011 within 100 square metres of the participants’ homes.

The participants, aged 40 to 69 at the start of the research, were taking part in the UK Biobank study. They had no history of a stroke or mini-stroke, defined as a temporary disruption to the brain’s blood supply, ischemic heart disease – cardiovascular complications caused by narrowing of the heart’s arteries – or cancer.

Over an average 12-year follow-up period, 5967 of the participants had a stroke, 2985 developed cardiovascular disease and 1020 people died due to any cause.

After accounting for other factors that can influence stroke risk, such as physical fitness levels, the researchers found that every 5 microgram per cubic metre (µg/m3) increase in fine particulate matter (PM2.5) that the participants were exposed to across a year was linked to a 24 per cent rise in their risk of a stroke.

Measuring less than 2.5 micrometres in diameter, PM2.5 is primarily released by exhaust pipes.

The World Health Organization recommends that our annual PM2.5 exposure shouldn’t exceed 5µg/m3. In the study, the participants who had a stroke had an average annual PM2.5 exposure of 10.03µg/m3, compared with 9.97µg/m3 among those who didn’t have a stroke.

“PM2.5 exposure could induce systemic oxidative stress, inflammation, atherosclerosis and elevates the risk of stroke,” says Lin. It is more easily inhaled than other pollutants and can therefore cause more conditions, he says.

“These results suggest that efforts to reduce exposures may be most beneficial to primary stroke prevention,” says Lin.

Among the participants who had a stroke, every 5µg/m3 increase to their annual nitrogen dioxide exposure was linked to a 4 per cent rise in their risk of cardiovascular disease post-stroke. A statistical analysis suggests this wasn’t a chance finding. Nitrogen dioxide is primarily released from burning fuel.

While PM2.5 and nitrogen dioxide exposure were linked with a heightened risk of a stroke itself and subsequent cardiovascular disease, respectively, neither increased the odds of a stroke-related death.

“This study elegantly confirms the increased risk of stroke due to air pollution in the UK Biobank population study, but interestingly suggests that the impact of air pollution may continue to adversely impact cardiovascular health even after the stroke occurred,” says Steffen Petersen at Queen Mary University of London.

“On a personal level, everyone, including stroke patients, may wish to consider personal measures to reduce exposure to air pollution, such as avoiding walking along polluted streets and rather take a less polluted route away from the main roads,” he says.

Journal reference: Neurology, DOI: 10.1212/WNL.0000000000201316