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Poor air quality linked to increased stroke risk

Issue: March 2016

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In the United States and China, higher pollution levels are associated with an increased number of strokes, according to research presented at the International Stroke Conference.

Investigators used data from the United States and China because they “are the world’s two largest emitters of greenhouse gases and responsible for about one-third of global warming to date,” Longjian Liu, MD, PhD, associate professor of epidemiology and biostatistics at Drexel University, Philadelphia, said in a press release.

Liu and colleagues analyzed air-quality data collected from 2010 to 2013 in 1,118 counties in 49 states in the United States and 120 cities in 32 provinces in China. Air quality in the United States was measured by the number of particular matter (PM) n the air: PM_2.5, emitted by industrial plants, cars and forest fires, was associated with the greatest health risks. Air quality in China was measured by the Air Pollution Index.

Longjian Liu

In the United States, the highest average PM_2.5 level (10.21 µg/m³) was observed in July and the lowest average level (7.63 µg/m³) was observed in October. Varying levels of PM_2.5 were reported across the 49 states (P = .019). Multilevel regression analysis revealed that the number of strokes increased by 1.19% per every 10-µg/m³ increase in PM_2.5 (P < .001). The researchers observed differences in stroke rates, with a more than 70% difference across the counties (P = .017) and 18.7% difference across the states (P = .047) included in the study. The data also demonstrated regional differences in air quality and stroke prevalence. The southern United States had the highest average PM_2.5 levels and the western United States had the lowest levels, which correlated with the highest prevalence of stroke observed in southern states (4.2%) and the lowest in western states (3%).

In China, the highest Air Pollution Index was reported in December: 75.76 in 2012 vs. 97.51 in 2013. The lowest Air Pollution Index was reported in July: 51.21 in 2012 vs. 54.23 in 2013. The prevalence of stroke was higher in Chinese cities with higher Air Pollution Index concentrations.

The researchers also found a correlation between temperature and stroke risk. “Seasonal variation in air quality can be partly attributable to the climate changes. In the summer, there are lots of rainy and windy days, which can help disperse air pollution. High temperatures create a critical thermal stress that may lead to an increased risk for stroke and other heat- and air quality-related illnesses and deaths,” Liu said. – by Tracey Romero

Reference:

Liu L, et al. Abstract 36. Presented at: International Stroke Conference; Feb. 16-19, 2016; Los Angeles.

Disclosures: The researchers report no relevant financial disclosures.