A stroke can happen unexpectedly – anytime, anywhere, sometimes without you even realizing it. Because of this, we tend to imagine that it’s something outside our control, like a lightning strike. Yet a new study led by Drs. Martin O’Donnell and Salim Yusuf from the McMaster University Population Health Research Institute shows that the majority of risk factors for stroke are preventable.
This study, called INTERSTROKE Phase II, builds on results from INTERSTROKE Phase I with over 13,000 additional patients, bringing the total to 26,919 participants from 32 countries. It was published last week in the leading medical journal, The Lancet.
Patients had suffered from either ischemic stroke (a blood clot blocking blood flow to the brain) or hemorrhagic stroke (a brain bleed). For every stroke patient, the study recruited an age and sex-matched healthy control to ensure unbiased results.
Patients were then scored based on a number of lifestyle factors: high blood pressure, physical activity, apolipoprotein (a measure of fats), diet, waist-to-hip ratio, psychosocial factors, smoking, cardiac causes, alcohol consumption, and diabetes mellitus. Each factor was studied for its strength of association with stroke. For example, how often patients with high blood pressure had a stroke versus patients with normal blood pressure.
The investigators then calculated the population attributable risk for each factor – an estimate of the strokes that could be reduced if an individual risk factor were eliminated.
High blood pressure ranked highest with a score of 47.9%, followed closely by physical inactivity and poor diet. All the risk factors together accounted for over 90% of stroke risk. This means that if we could fix or reverse all these factors, we could reduce the number of strokes by over 90%. Pretty amazing!
Although the total of all stroke factors was similar in all regions studied, their relative contributions varied. For example in North America, Western Europe, and Australia (one region) the association between alcohol intake and stroke was quite low, whereas in South Asia (second region) and Africa (third region) it was higher. On the other hand, poor diet was highly correlated with stroke in North America, Western Europe, and Australia, but had a low correlation in South Asia and Africa.
This type of information could inform regional stroke prevention programs or campaigns. Anti-drinking campaigns might be more important in Africa while a heart healthy diet should be stressed in North America.
A positive message
In 2012, more than 13,000 Canadians died as the result of a stroke and more than 400,000 Canadians are living with long-term stroke disability. This study shows that we have the power to decrease these numbers.
Cindi Morshead, Professor at the University of Toronto and stroke researcher, is excited by this positive message.
“These findings offer hope by telling us that we can take control and eliminate the risk factors that increase our chance of suffering a stroke. And by doing so you will be protecting your most important asset – your brain.”