Pollution has many implications for public health; the most obvious concern is the respiratory system. A recent study has linked higher pollution levels to a higher total number of strokes, something researchers say affirms the growing evidence that overall air quality and climate change contribute to cardiovascular disease.

Presented at the International Stroke Conference, the study utilized data from both 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,” said Dr. Longjian Liu, lead study author and an associate professor of epidemiology and biostatistics at Drexel university, in a statment. The research is the first of its kind, investigating the interaction between stroke prevalence, air quality, and the potential effect of temperatures on the association.

The research team looked at air quality data from between 2010 and 2013, ranging across 1,118 counties in 49 states in America and 120 cities in 32 provinces in China. Particles in the air, including dust, liquid droplets, and smoke, are called particulate matter (PM) and measured in micrometers. The greatest health risk to humans is posed by particles less than 2.5 micrometers in diameter (PM2.5), particles produced by combustion from cars, forest fires, power plants, and other sources.

According to the study, the total number of stroke cases rose 1.19 percent for each 10 micrograms per cubic meter of air increase of PM2.5. In addition, Liu said, the team found a significant regional variation in PM2.5 levels that was linked to the number of stroke cases — for example, the southern region of America had the highest average annual Pm2.5, while the West had the lowest, which correlates with the fact that the South had the highest prevalence of stroke and the West had the lowest. The temperature also had an impact on both air quality and risk of stroke.

“Seasonal variations in air quality can be partly attributable to the climate changes,” Liu said. “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 added that stroke patients are also in danger of dehydration due to high temperature, and that women and the elderly appear to be more vulnerable to stroke due to air quality and heat-related diseases.

Stroke is among the leading causes of death in the United States, killing nearly 129,000 people every year. Worldwide prevalence stands at 33 million, and stroke is the second-leading cause of global death behind heart disease. Liu said that while people cannot control air quality, the findings provide evidence for public health policymakers to better protect citizens.

Source: Liu L, Yang X, Jia F, Wang M. Mapping and Multilevel Modeling of Climate Change and Air Pollution with Risk of Stroke in the United States and China: Findings from the Drexel-SARI Low Carbon and healthy City Study. American heart Association’s International Stroke Conference 2016. 2016.