Prevention of stroke is a major public health priority, but the variation by region should influence the development of strategies for reducing stroke risk, say the authors of the study published in The Lancet.

Stroke is a leading cause of death and disability, particularly in low-income and middle-income countries. The two major types of stroke include ischaemic stroke caused by blood clots, which accounts for 85% of strokes, and haemorrhagic stroke or bleeding into the brain, which accounts for 15% of strokes.

The study led by Dr. Martin O’Donnell and Dr. Salim Yusuf of the Population Health Research Institute at McMaster and collaborators from 32 countries, builds on findings from the first phase of the INTERSTROKE study which identified ten modifiable risk factors for stroke in 6,000 participants from 22 countries. This full-scale INTERSTROKE study added 20,000 individuals from 32 countries in Europe, Asia, America, Africa and Australia, and sought to identify the main causes of stroke in diverse populations, young and old, men and women and within subtypes of stroke.

“This study has the size and scope to explore stroke risk factors in all major regions of the world and within key populations,” said O’Donnell, a principal investigator for the PHRI and professor of translational medicine at HRB-Clinical Research Facility, NUI Galway.

“We have confirmed the ten modifiable risk factors associated with 90% of stroke cases in all regions, young and older and in men and women. The study also confirms that hypertension is the most important modifiable risk factor in all regions, and the key target in reducing the burden of stroke globally.”

The investigators looked at the different risk factors, and determined the proportion of strokes which would be cut if the risk factor disappeared.

The number of strokes would be practically cut in half (48%) if hypertension was eliminated; trimmed by more than a third (36%) if people were physically active; and shaved by almost one fifth (19%) if they had better diets. In addition, this proportion was cut back by 12% if smoking was eliminated; 9% for cardiac (heart) causes, 4% for diabetes, 6% for alcohol intake, 6% for stress, and 27% for lipids (the study used apolipoproteins, which was found to be a better predictor of stroke than total cholesterol).

Many of these risk factors are known to also be associated with each other (such as obesity and diabetes), and when were combined together, the total for all 10 risk factors was 91%, which was similar in all regions, age groups and in men and women.

However, the importance of some risk factors appeared to vary by region. For example, the importance of hypertension ranged from practically 40% in Western Europe, North America, and Australia to 60% in Southeast Asia. The risk of alcohol was lowest in Western Europe, North America and Australia but highest in Africa and south Asia, while the potential impact of physical inactivity was highest in China.

An irregular heart rhythm, or atrial fibrillation, was significantly associated with ischaemic stroke in all regions, but was of greater importance in Western Europe, North America and Australia, than in China or South Asia.

However, when all 10 risk factors were included together, their collective importance was similar in all regions.

“Our findings will inform the development of global population-level interventions to reduce stroke, and how such programs may be tailored to individual regions,” said Yusuf, a professor of medicine of McMaster’s Michael G. DeGroote School of Medicine and director of the PHRI. “This includes better health education, more affordable healthy food, avoidance of tobacco and more affordable medication for hypertension and dyslipidaemia.”

Along with the study, The Lancet published a related comment from New Zealand researchers Valery L. Feigin and Rita Krishnamurthi of the National Institute for Stroke and Applied Neurosciences, of Auckland’s University of Technology.

They said the key messages from the study were that stroke is a highly preventable disease globally, regardless of age and sex; that the relative importance of modifiable risk factors means there should be development of regional or ethnic-specific primary prevention programs, and that additional research on stroke risk factors is needed for countries and ethnic groups not included in INTERSTROKE.

“Now is the time for governments, health organizations, and individuals to proactively reduce the global burden of stroke. Governments of all countries should develop and implement an emergency action plan for the primary prevention of stroke,” they wrote.

“We started our study on Luzon in 2000 because we knew at the time that most of the native mammal species on the island were unique to the island, and we wanted to understand why that is the case. We did not expect that we would double the number already known,” said Lawrence Heaney, the project’s leader, who is the Negaunee Curator of Mammals at The Field Museum in Chicago.

Luzon is the largest island in the Philippines; at about 40,000 square miles, it’s a bit larger than Indiana. According to the authors, Luzon has never been connected to any continental land–the species have been isolated, like the animals that live in Hawaii. But Luzon is much larger and at least five times older than the oldest island in Hawaii, and so has had time for the few species that arrived from the Asian mainland to evolve and diversify greatly.

On islands, scientists sometimes see a “sped-up” version of evolution–when animals are closed off from the rest of the world, in places where there are few or no predators or competitors, they are able to branch out into special adaptations, eventually forming new species. And not only is the island of Luzon isolated, but it’s covered in mountains. The mountaintops form what scientists call “sky islands”–little pockets of distinctive habitat that the animals further adapt to. “The animals are isolated high on the scattered mountains, so they inevitably diverge. Given enough time, you begin to see huge biodiversity,” explained Heaney. “In the process of trying to understand how that happens, we doubled the number of known species on Luzon.”

Among the 28 new species discovered by the team are four species of tiny tree-mice with whiskers so long they reach nearly to their ankles, and five species of mice that look like shrews and feed primarily on earthworms. Most of the new species live in tropical cloud forest high in the mountains, where frequent typhoons can drop four or five meters (12 to 15 feet) of rain per year.

“All 28 of the species we discovered during the project are members of two branches on the tree of life that are confined to the Philippines,” according to Eric Rickart, a team member who is based at the Natural History Museum of Utah. “There are individual mountains on Luzon that have five species of mammals that live nowhere else. That’s more unique species on one mountain than live in any country in continental Europe. The concentration of unique biodiversity in the Philippines is really staggering.”

Luzon also supports 57 species of bats; most live in the hot, humid lowlands. These include the golden-crowned flying fox, which is one of the heaviest bats in the world at up to two and a half pounds. Another, the lesser flat-headed bat, is so tiny that it can roost inside the hollow spaces inside bamboo stems.

“We also wanted to learn more about the conservation status of these wonderful animals,” said Danny Balete, a Research Associate at the Field Museum who is based in the Philippines. “The Philippines is one of the most heavily deforested countries in the tropics; only about seven percent of the old-growth tropical forest is left. We learned that quite a few of the species are seriously threatened by habitat loss and over-hunting, but none are yet extinct.” Luzon has a human population of about 50 million, including about 23 million in greater Manila, the country’s capital. “Protecting all of these species from extinction is going to be a big challenge. The good news is that when the native forest is allowed to regenerate, the native mammals move back in, and the pest rats get kicked out.”

Other co-authors of the paper are based at the University of the Philippines, the University of Minnesota, and Florida State University. Heaney, Balete, and Rickart are also authors of a book about the mammals of Luzon Island, just published by Johns Hopkins University Press, that will be used in the Philippines as a college-level textbook. The team works closely with conservation organizations and the Philippine government, and many of their recommendations regarding expanded and new national parks have been adopted.

“Learning about the tremendous diversity of mammal species present on Luzon is crucial to conservation efforts,” explained Heaney. “In order to be effective at conserving an environment, we have to know what’s out there.”