According to a new study, residing in areas with increased air pollution is linked to a greater risk of in-hospital death from stroke, and the risk changes based on the size of the air pollution particles.
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The study was reported on May 25th, 2022, in the journal Neurology®, the medical journal of the American Academy of Neurology.
The study observed three sizes of air pollution particulate matter. Particulate matter includes solids or liquids suspended in the air. Submicron particulate matter, the so-called PM1, is less than 1 μm in diameter and consists of soot and smog.
Fine particulate matter, PM2.5, is below 2.5 μm in diameter and consists of fly ash from coal combustion. Respirable particulate matter, PM10, is less than 10 μm in diameter and consists of cement dust.
Air pollution has been previously linked to a greater risk of stroke, and stroke is a leading cause of death worldwide. What is lesser known is how the different sizes of particulate matter affect that risk. Our research found that the size of air pollution particles may affect a person’s risk of dying from stroke.
Hualiang Lin Ph.D, Study Author, Sun Yat-sen University
For the study, scientists analyzed electronic medical records in China to determine more than 3.1 million hospitalizations for stroke, both ischemic strokes resulting in a blood clot, and hemorrhagic strokes caused due to bleeding in the brain. Participants were of an average age of 67. Among this group, 32,140 people, or 1%, died of a stroke while being hospitalized.
Scientists determined individual levels of air pollution exposure for every participant by making use of their home addresses and an air pollution data source that documents daily concentrations of different kinds of particulate matter.
Furthermore, scientists evaluated seven-day air pollution exposure just before hospitalization for stroke, which was around 31.38 micrograms per cubic meter (µg/m3) of PM1, 45.43 µg/m3 of PM2.5, and 78.75 µg/m3 of PM10.
Also, they evaluated the average daily exposure of a person to pollution particles in the year prior to hospitalization. This was found to be around 32.98 µg/m3 of PM1, 49.08 µg/m3 of PM2.5, and 87.32 µg/m3 of PM10.
Following the adjustment for factors like sex, age, diabetes, socioeconomic status, and high blood pressure, scientists discovered each 10 µg/m3 increase in yearly average exposure to particulate matter that was linked to a greater risk of dying of stroke while hospitalized.
This had a 24% greater risk for exposure to PM1, an 11% higher risk for exposure to PM2.5, and a 9% greater risk for exposure to PM10. The seven-day average exposure to particulate matter consisted of around a 6% increased risk for exposure to PM1, a 4% increased risk for exposure to PM2.5, and a 3% increased risk for exposure to PM10.
The risks were more powerful in people with ischemic stroke compared to people with hemorrhagic stroke. The biggest risk of death from stroke was in people with ischemic stroke and exposure to the smallest air pollution particles, PM1.
Also, scientists discovered that a decrease in PM10 would have the biggest impact on decreasing overall deaths from stroke. This helps decrease the number of hospital deaths by 21% for long-term exposure and 10% for short-term exposure.
Lin stated that it is essential to recognize that the study outcomes do not prove that air pollution results in stroke deaths, they only exhibit an association.
Our study includes measurements of PM1, which may be small enough to be inhaled deeply into lungs, pass through lung tissue, and circulate in the bloodstream. Obtaining a deeper understanding of the risk factors of all particulate matter sizes and the magnitude of their possible effects may help reduce the number of deaths and improve the outcomes for people with stroke.
Hualiang Lin Ph.D, Study Author, Sun Yat-sen University
The study’s limitation was that outcomes were not adjusted for a smoking status or the severity of stroke in a person. Scientists also only analyzed air pollution exposure at a person’s present residence and not at earlier residences.
Journal Reference:
Cai, M., et al. (2022) Association of Ambient Particulate Matter Pollution of Different Sizes With In-Hospital Case Fatality Among Stroke Patients in China. Neurology. doi.org/10.1212/WNL.0000000000200546.