Exposure to air pollution increases the risk of stroke by more than half.

Air pollution contains many toxic substances, including chemicals, gases, and particulate matter – a mixture of solid particles and liquid droplets that exert neuroinflammatory effects. Exposure to air pollution promotes oxidative stress and increases the risk of developing many chronic diseases, such as cardiovascular disease, cancer, hypertension, and diabetes, markedly shortening people’s lives. Findings from a 2003 study suggest that exposure to air pollution is associated with an increased risk of stroke.

A stroke is a neurological disorder characterized by the interruption of blood flow to the brain. Strokes are typically classified as either ischemic or hemorrhagic. Ischemic strokes, which account for approximately 87 percent of all strokes, are characterized by the blockage of an artery. Hemorrhagic strokes, which account for 13 percent of strokes, are characterized by bleeding from a blood vessel that supplies the brain.

The researchers reviewed admission data from hospitals in and around Kaohsiung, Taiwan, an industrial area known for its high levels of air pollution. They obtained air quality assessments of the same area via government monitoring stations that provided measurements of gases (sulfur dioxide, nitrogen dioxide, carbon monoxide, and ozone) and particulate matter with diameters of 10 micrograms (PM10) or less. Because weather influences air quality, they also collected humidity and temperature readings from the government weather agency.

They found that exposure to higher levels of nitrogen dioxide and PM10 was associated with increased risk of stroke, especially on warm days (68°F or warmer). The risk of ischemic stroke increased by 55 percent for greater nitrogen dioxide exposure and by 46 percent for greater PM10 exposure. The risk for hemorrhagic stroke increased by 54 percent with greater exposure to either nitrogen dioxide or PM10.

These findings suggest that exposure to common air pollutants, especially during warmer weather, increases the risk of stroke. The investigators posited that this increased risk is due to the inflammatory effects of particulate matter and the increase in plasma viscosity and serum cholesterol levels that occur with exposure to high temperatures and humidity.

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