Saturday, November 07, 2015

Top Risk Factors for Stroke: The INTERSTROKE Study

Bill Yates
Brain Posts
Posted 15th July 2010

Many studies have examined the role of individual risk factors in stroke. Few have been large enough to provide a comprehensive overview of a multitude of risk factors across many populations. The INTERSTROKE study is one of the largest and most extensive studies of risk factors for stroke.

O'Donnell and colleagues report on the risk factors for stroke identified in a study across 22 countries in a recent Lancet manuscript. The key aims of the INTERSTROKE study include:
  • establish the association of risk factors for stroke and stroke subtypes
  • assess the relative attributable risk for overall stroke burden
  • examine differences between risk factors for stroke and myocardial infarction
Stroke can be subtypes into ischemic stroke (brain vessel clot) and intracerebral hemorrhagic stroke (brain vessel bleed). When combining these two types of stroke individual risk factor population-attributable risks for all stroke in the study were:
  • history of hypertension or blood pressure >160/90 (51.8%)
  • low regular physical activity (28.5%)
  • elevated waist-to-hip ratio (26.5%)
  • blood lipid level (ratio of ApoB to ApoA) (24.9%)
  • current smoking (18.9%)
  • poor diet (18.8%)
  • cardiac causes (arrhythmia, MI or valvular disease) 6.7%
  • depression (5.2%)
  • diabetes mellitus (5.0%)
  • psychosocial stress (4.6%)
  • alcohol intake >30 drinks per month (3.8%)
The individual attributable risks estimate the size of the burden for each risk factor. It is possible then to estimate the reduction in total stroke if the factor could be eliminated. For example, if all individuals reduced alcohol intake to less than 30 drinks per month, stroke prevalence rates would be estimated to be reduced by 3.8%. The attributable risk rates add up to greater than 100% because of overlap in the distribution of the individual risk factors. To address this issue, multivariate statistic techniques are needed.

The study used multivariate techniques to examine how combining the risk factors accounts for stroke risk variance. Remarkably, these factors in combined models account for up to 90% of the variance for all stroke prevalence as well as for the prevalence of the two stroke subtypes.

To simply the model, the authors summarize that five risk factors account for 80% of stroke risk:
  • hypertension
  • current smoking
  • abdominal obesity
  • diet
  • low physical activity
The take home message from this study: "Targeted interventions that reduce blood pressure and smoking, and promote physical activity and a healthy diet, could substantially reduce the global burden of stroke."

Photo of University of Oklahoma Sooner baseball player Garrett Buechele batting at 2010 College World Series courtesy of Yates Photography.

O'Donnell MJ, Xavier D, Liu L, Zhang H, Chin SL, Rao-Melacini P, Rangarajan S, Islam S, Pais P, McQueen MJ, Mondo C, Damasceno A, Lopez-Jaramillo P, Hankey GJ, Dans AL, Yusoff K, Truelsen T, Diener HC, Sacco RL, Ryglewicz D, Czlonkowska A, Weimar C, Wang X, Yusuf S, & INTERSTROKE investigators (2010). Risk factors for ischaemic and intracerebral haemorrhagic stroke in 22 countries (the INTERSTROKE study): a case-control study. Lancet, 376 (9735), 112-23 PMID: 20561675.

See the original article:

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