New York, Feb 20 (IANS): Rising levels of pollution have led to an increase in the number of strokes, revealed a study, reaffirming the growing evidence that climate change and overall air quality contributes to heart disease.

The results showed that particles less than 2.5 mm in diameter (PM2.5) pose the greatest health risks due to their small size (1/30th diameter of a human hair and not visible to the human eye). They are created from combustion from cars, power plants, forest fires and others.

Researchers also found that temperature had an impact on air quality and risk of stroke.
High temperatures create a critical thermal stress that may increase the risk of stroke and other heat-and air quality-related illnesses and deaths.

"Patients with stroke are in danger of dehydration due to high temperatures in the summer and pneumonia, influenza and other respiratory diseases in winter," said Longjian Liu, associate professor at the Drexel University in Philadelphia in the US.

Women and the elderly also appear more vulnerable to stroke risk due to air quality and heat-related diseases, he added.

The study data was collected from the US and China -- "the world's two largest emitters of greenhouse gases and responsible for about one-third of global warming to date," the authors said.

The team evaluated air quality data collected between 2010 and 2013 from 1,118 counties in 49 states in America and from 120 cities in 32 provinces in China. 

Across the two countries, researchers found that the total number of stroke cases rose 1.19 percent for each 10 mg per cubic metre air (µg/m3), an increase of PM2.5.

Overall, the southern region of America had the highest average annual PM2.5 while the West had the lowest -- which correlates with the fact that people living in the South had the highest prevalence of stroke at 4.2 percent compared with those in the West who had the lowest at three percent, Liu said.

Stroke is the fifth leading cause of death in the US killing nearly 129,000 people every year, and is a leading cause of disability.

Worldwide, the prevalence of stroke stood at 33 million, with 16.9 million people suffering their first stroke, and is the second-leading cause of global deaths behind heart disease.

The study was presented at the American Stroke Association's International Stroke Conference 2016.