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Most Strokes Worldwide Caused by Modifiable Lifestyle Factors; Air Pollution Is to Blame for One-Third of Cases

Fitzgerald, Susan

doi: 10.1097/
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In an analysis of risk factors that contribute to the burden of stroke in 188 countries, researchers found that lifestyle factors related to poor diet, low physical activity, and high blood pressure, obesity, smoking, unhealthy diet, and low physical activity continue to be major drivers of stroke, but air pollution has emerged as a formidable risk factor, especially in low-income and middle-income countries.

Air pollution, both outdoor and indoor, is now among the leading causes of stroke worldwide, accounting for approximately one-third of stroke burden in 2013, according to a detailed analysis of data from 188 countries.

High blood pressure, obesity, smoking, unhealthy diet, and low physical activity continue to be major drivers of stroke, but air pollution has emerged as another formidable risk factor, especially in low-income and middle-income countries.

Stroke affects 17 million people worldwide each year, leaving six million people dead and 11 million with lasting disability, according to the report published in the June 9 online edition of The Lancet Neurology. The new snapshot of global stroke burden offers insight into the challenges medical and public health workers face as they devise stroke prevention strategies.

“Our results suggest that more than 90 percent of the stroke burden is attributable to modifiable risk factors, and achieving control of behavioral and metabolic risk factors could avert more than three-quarters of the global stroke burden,” the research team reported. They noted that behavioral risk factors — smoking, poor diet, and low physical activity, when combined — account for 74.2 percent of stroke burden, while metabolic risk factors — high systolic blood pressure and high body mass index (BMI), when combined — account for 72.4 percent of stroke burden.

“This analysis suggests that stroke is now more a lifestyle disease, and that far more attention needs to be paid to the modification of behavioral risks on the individual and population level than it was before,” lead author Valery Feigin, MD, PhD, professor of neurology and epidemiology at Auckland University of Technology in New Zealand, told Neurology Today. In addition, “measures to reduce air pollution should be one of the main priorities for combating stroke across the globe,” Dr. Feigin said in an email.

The new analysis considered both environmental air pollution and household air pollution, usually caused by burning solid fuels.

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The new analysis is based on data from the Global Burden of Disease Study 2013, which pulled together published and unpublished stroke and other relevant epidemiological data from 1990-2013 from every region of the world. Seventeen stroke risk factors were considered by age, sex, and region. In addition, the researchers used a measure called stroke-related DALYs (disability-adjusted life-years) to calculate the burden of stroke from any given risk factor and their clusters. DALYs for a disease or health condition are calculated as the sum of the years of life lost due to premature mortality and/or disability for people living with the health condition or its consequences.

The researchers found that some risk factors played a larger role than others depending on the region. For instance, household air pollution was the third largest risk factor for stroke in central, eastern, and western sub-Saharan Africa and south Asia, although it did not rank in the top 10 in North America, central, eastern, and western Europe. The top five risk factors for stroke in the US and United Kingdom are high blood pressure, high BMI, a diet low in fruit and vegetables, and smoking. The top five risk factors in China are high blood pressure, a diet low in fruit and high in sodium, smoking, and environmental air pollution.

Of all the stroke risk factors analyzed in the study, second-hand smoking declined the most globally between 1990 and 2013, with more improvement seen in developed nations than in developing ones.

The study, funded by the Melinda and Bill Gates Foundation and others, was limited by the fact that comprehensive health data were not available from many countries, particularly those in developing parts of the world. Still, Dr. Feigin said the analysis helps underscore the need to put more public health attention and funding into primary stroke prevention efforts, and offers some direction on on how strategies might be best tailored and prioritized.

Around 1994, “the global burden of disease shifted from infectious disease to non-communicable disease,” he said. “Stroke is the second cause of death and the third cause of disability in the world.”

Dr. Feigin noted that while the incidence and mortality rates of stroke are on the decline in the US and some other high-income countries, “the number of people affected by stroke, surviving stroke, and dying from stroke is increasing in almost every country of the world, including the United States.”

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Other stroke experts interviewed by Neurology Today agreed that the public often assumes that infectious diseases such as HIV, malaria, Ebola, and now Zika are the biggest global threats, when in fact ischemic heart disease and stroke top the list.

Jerome Chin, MD, PhD, founder and president of the Alliance for Stroke Awareness and Prevention Project (ASAPP), which supports stroke prevention projects in developing countries, said the new study highlights “once again the importance of screening for, diagnosing, and treating high blood pressure.”

“The number one risk factor for stroke in every region of the world is high blood pressure,” causing almost two-thirds of the global burden of stroke as measured by DALYs, said Dr. Chin, adjunct professor of neurology at New York University Langone Medical Center. Fueling the global stroke epidemic are urbanization, population growth and aging, and adoption of western lifestyle habits in developing countries, leading to unhealthy diets, physical inactivity, and obesity, he said.

“In most low- and middle-income countries, the majority of adults do not know their blood pressure, and rates of treatment and control are very low,” Dr. Chin said. The ASAPP supports community-based project sites in Tanzania and Nepal.

“There is an urgent need to increase domestic health spending and international support for non-communicable diseases,” Dr. Chin said. “A priority should be placed on providing affordable and accessible primary health care services to address the leading risk factors for cardiovascular diseases, including stroke and ischemic heart disease,” Dr. Chin said.

He cited the need for policies and programs to promote healthy lifestyle choices, including regular physical activity, low-salt diets, and smoking cessation. He also favors government regulations aimed at reducing consumption of unhealthy foods and controlling air pollution.

Aaron Berkowitz, MD, assistant professor of neurology at Harvard Medical School and Brigham and Women's Hospital, said the new study likely underestimates the extent of stroke risk worldwide because comprehensive health data are lacking in many parts of the world.

Dr. Berkowitz spoke to Neurology Today from Haiti, where he was training primary care physicians in neurologic care, including stroke. He said the lack of health care resources in poorer countries is a major impediment to devising better strategies for stroke prevention. In Haiti, for instance, there is only one neurologist for a country of 10 million people, he said.

Dr. Berkowitz said more money is needed to fund stroke prevention efforts around the globe. He wrote an article for Neurology in May 2015 in which he noted that in 2011 global HIV/AIDS programs received $7.7 billion in funds, which amounted to 25 percent of global health funding. In comparison, non-communicable diseases combined (including stroke) received $337 million, just 1.2 percent of global health funding.

Dr. Berkowitz told Neurology Today he is not suggesting that HIV/AIDS and other infectious diseases should get less funding, but that stroke, which is a major killer worldwide, should get more.

“Seventy percent of global strokes actually occur in low and middle-income countries,” where the need for more health clinics and services is often dire, he said.

The air pollution connection is important, Vladimir Hachinski, MD, DSc, FAAN, professor of neurology at University of Western Ontario, told Neurology Today.

Dr. Hachinski, who coauthored an accompanying editorial with Mahmoud Reza Azarpazhooh, MD, associate professor of neurology at the Mashhad University of Medical Sciences in Iran, said: “We have known about the relationship between air pollution and stroke. But this study really puts that risk into a global perspective.”

Air pollution can't be viewed as another country's problem, they wrote. “With the ceaseless air stream across oceans and continents, what happens in Beijing happens in Berlin.”

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•. Feigin VL, Roth GA, Naghavi M, et al.for the Global Burden of Diseases, Injuries, and Risk Factors Study 2013 and Stroke Experts Writing Group. Global burden of stroke and risk factors in 188 countries, during 1990-2013: A systematic analysis for the Global Burden of Disease Study 2013 Lancet Neurol 2016; Epub 2016 Jun 9.
•. Hachinski V, Azarpazhooh MR. Stroke is a burdensome but preventable brain disorder Lancet Neurol 2016: Epub 2016 Jun 9.
© 2016 American Academy of Neurology