Air pollution increases our chances of having a stroke and its subsequent complications

Living in a highly polluted area may increase the likelihood of suffering a stroke and its complications. Air pollution has previously been linked to strokes; however, Hualiang Lin and his colleagues at Sun Yat-sen University in China wanted to determine the risk among individuals with no history of stroke. Also of interest was the effect of air pollution on post-stroke complications, such as cardiovascular disease.

The team evaluated the air pollution exposure of over 318 thousand British citizens. Between January 2010 and January 2011, independent researchers monitored air pollution within 100m2 of the participants' homes. The participants, who ranged in age from 40 to 69 at the outset of the study, participated in the UK Biobank study. They had no history of ischemic heart disease – cardiovascular complications caused by narrowing of the heart's arteries – or cancer.

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

During an average 12-year period of follow-up, 5,967 participants had a stroke, 2,985 developed cardiovascular disease, and 1,020 participants died from any cause. After accounting for other factors that can affect our stroke risk, such as our level of physical activity, every 5 microgram per cubic metre (g/m3) increase in fine particulate matter (PM2.5) that the participants were exposed to over the course of a year was associated with a 24% increase in their risk of a stroke.

PM2.5, which has a diameter of less than 2.5 microns, is primarily emitted by exhaust pipes. The World Health Organization suggests that our annual PM2.5 exposure should not exceed 5 micrograms per square meter. In the study, participants who experienced a stroke had an average annual PM2.5 exposure of 10.03g/m3, compared to 9.97g/m3 for participants who did not experience a stroke.

“PM2.5 exposure could induce systemic oxidative stress, inflammation, atherosclerosis and elevates the risk of stroke,” says Lin. According to him, it is more easily inhaled than other pollutants and therefore causes more diseases. “These results suggest that efforts to reduce exposures may be most beneficial to primary stroke prevention,” says Lin.

Every 5g/m3 increase in participants' annual nitrogen dioxide exposure was associated with a 4% increase in their risk of cardiovascular disease following a stroke. A statistical analysis indicates that this was not a random occurrence. Nitrogen dioxide is primarily produced by the combustion of fuel. While exposure to PM2.5 and nitrogen dioxide was associated with an increased risk of stroke and subsequent cardiovascular disease, neither increased the risk of 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, UK.

“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.”

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