Each year around the world, approximately 15 million people have a stroke. Of these, 6 million die and 5 million are left permanently disabled, making stroke the second leading cause of disability. Now, a new study implicates air pollution as a leading risk factor for stroke worldwide.
The study, which is published in The Lancet Neurology, finds that air pollution is associated with about a third of the global stroke burden; this includes environmental and household air pollution, researchers say.
Using data from the Global Burden of Disease Study, the researchers were able to estimate the disease burden of stroke associated with 17 risk factors across 188 countries.
They say theirs is the first study to run a detailed analysis on global stroke risk factors, particularly as they relate to stroke burden on global, regional, and national scales.
A stroke occurs when the brain's blood supply is blocked or when a blood vessel bursts, resulting in a loss of oxygen to the brain that, in turn, injures or kills brain cells.
Having a stroke can result in death or permanent disability, including loss of vision or speech, paralysis, and confusion.
The researchers of this latest study - led by Dr. Valery L. Feigin, of Auckland University of Technology in New Zealand - say that until now, the effect of modifiable risk factors on the increasing global burden of stroke has been unclear.
However, gaining an understanding about this effect is "crucial for informing stroke prevention strategies."
90 percent of global stroke burden linked to modifiable risk factors
To get a clearer picture, the researchers
They found that the 10 leading stroke risk factors around the world were high blood pressure, low fruit intake, high body mass index (BMI), high sodium intake, smoking, low vegetable intake, environmental air pollution, household pollution, low whole grain intake, and high blood sugar.
In detail, the researchers discovered that around 30 percent of disability associated with stroke is linked to air pollution, which is especially high in developing countries compared with developed countries, at 33.7 percent and 10.2 percent, respectively.
They also found that over 90 percent of the global burden of stroke is associated with modifiable risk factors. According to the team, control of these risk factors could prevent nearly 75 percent of all strokes.
"Our findings are important for helping national governments and international agencies to develop and prioritize public health programs and policies. Governments have the power and responsibility to influence these risk factors through legislation and taxation of tobacco, alcohol, salt, sugar or saturated fat content, while health service providers have the responsibility to check and treat risk factors such as high blood pressure."
Dr. Valery L. Feigin
Interestingly, the team also reported on the top five risk factors for stroke in certain countries:
- United Kingdom and United States: high blood pressure, high BMI, low fruit intake, low vegetable intake, smoking
- India: high blood pressure, low fruit intake, household air pollution, low vegetable intake, high sodium intake
- China: high blood pressure, low fruit intake, high sodium intake, smoking, environmental air pollution.
'Air pollution is a global problem'
Due to a lack of data, the researchers note that they were unable to include other important stroke risk factors, including atrial fibrillation, substance abuse, or other health conditions.
Additionally, they were unable to account for patterns of certain risk factors, including smoking levels, BMI levels, or underlying genetic risk factors.
Although their study does not differentiate between ischemic and hemorrhagic stroke, the authors note that global, regional, and national policies look at overall stroke risks.
Prof. Feigin notes that taxation has been proven as an effective strategy to reduce smoking and high intakes of salt, sugar, and alcohol. "All it takes is recognition of the urgent need to improve primary prevention, and the good will of the governments to act," he adds.
In a linked comment, Prof. Vladimir Hachinski - of the University of Western Ontario in Canada - and Dr. Mahmoud Reza Azarpazhooh - of Mashhad University of Medical Sciences in Iran - write:
"The most alarming finding was that about a third of the burden of stroke is attributable to air pollution. Although air pollution is known to damage the lungs, heart, and brain, the extent of this threat seems to have been underestimated. Air pollution is not just a problem in big cities, but is also a global problem. With the ceaseless air streams across oceans and continents, what happens in Beijing matters in Berlin."