INTERSTROKE: Global Study Finds 10 Risk Factors Explain Almost 90% of Stroke Risk

May 05, 2014

MELBOURNE, AUSTRALIA — A large case-control study of stroke has identified a number of modifiable risk factors that explain approximately 90% of the population-attributable risk, with hypertension being the most important risk factor. The other risk factors that contribute most to the risk of stroke include lipid levels, physical inactivity, smoking, and diet.

In addition, larger waist-to-hip ratios, a history of diabetes, increased alcohol intake, psychosocial stress and/or depression, and cardiac causes all contribute to stroke.

The findings, if they sound familiar, are from the INTERSTROKE study, a study that was presented here at the World Congress of Cardiology 2014 Scientific Sessions . These new results are in line with the first phase of the INTERSTROKE study presented and published four years ago. Whereas the first feasibility phase of the case-control study included just 6000 patients from 22 countries, this second phase includes more than 27 011 individuals, including 13 604 with stroke and 13 407 age- and sex-matched controls. Patients were recruited from centers in North America; Western, Central, and Northern Europe; the Middle East; South America; China, South and Southeast Asia; and Africa.

Presenting the results, Dr Martin O'Donnell (Population Health Research Institute, Hamilton, ON) said the purpose of the study is to help identify regional variations in the importance of various risk factors for stroke. The present analysis, which is still preliminary, did show there was variation in the population-attributable risk for all 10 risk factors for all types of stroke, but more than 87% of the risk of stroke could be explained by these 10 risk factors.

"One aspect that's interesting is that this study helps us understand the genetic contributions to stroke," O'Donnell told heartwire . "The days of us thinking that genetics would have a large main effect, that it would be up there with lipids, is untrue. Likely, genetics have a modifying effect. If you carry a certain polymorphism, you're more prone to blood-pressure effects. To truly tease out these multiple risk factors, we need vary large sample sizes. We conducted this study so that we could answer such pivotal questions."

The average age of patients in INTERSTROKE is 62 years, but there were 1559 individuals younger than 45 years of age. In terms of stroke subtype, there were 10 349 ischemic strokes and 3039 intracerebral hemorrhages.

Regarding the risk factors for ischemic stroke, those who had a clinical event were three times more likely to have hypertension compared with controls and were twice as likely to have an elevated apolipoprotein B/apolipoprotein A1 (apoB/A1) ratio. In addition, cardiac causes were also a risk factor for ischemic stroke. Current smoking, obesity, poor diet, and physical inactivity, among others, were also associated with an increased risk of ischemic stroke.

Regarding intracerebral hemorrhage, those who had an event were nearly eight times more likely to have hypertension compared with controls. Current smoking, obesity, poor diet, alcohol binges, and psychosocial stress were also more significantly common among those with an intracerebral hemorrhage compared with controls.

To heartwire , O'Donnell said INTERSTROKE allows researchers and clinicians to get a better handle on the risk factors for intracerebral hemorrhage, something that wasn't fully understood before. He cautioned that the data still need to be analyzed further and noted that investigators completed the study only in March. The researchers plan to investigate the risk factors in more depth—for example, analyzing hemoglobin A1c levels instead of just a history of diabetes and teasing out the dietary risk scores better—and will publish these data when they are available.

"The key is that studies like this, in stroke, can be done, with the perseverance of the investigators," said O'Donnell. "They did this because they wanted to do something about stroke, wanted to put it on the map." The massive undertaking of the INTERSTROKE investigators gives them confidence that the risk factors identified are not skewed toward any particular population but instead representative of a global population, he added.

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