'Nine out of 10 strokes preventable,' claims study

"Nine out of 10 strokes preventable if people follow 10 health rules," The Daily Telegraph reports.

The news comes from a large study that found the top 10 risk factors for stroke are preventable.

The 10 main risk factors for stroke are:

• high blood pressure
• smoking
• too much alcohol
• diabetes
• poor diet
• lack of exercise
• high cholesterol
• heart problems
• obesity
• stress

Canadian researchers estimated around 9 out of 10 strokes worldwide, including among people in the UK, could be caused by these risk factors – many of which can be avoided.

Strokes are a major health problem in the UK. Every year, around 110,000 people in England have a stroke. The condition is the third largest cause of death after heart disease and cancer.

This study compared the lifestyles of people who had a stroke with those who had not, involving nearly 27,000 participants from 32 countries.

But the 9 out of 10 figure is only an estimate. We don't know that these risk factors are the definite cause of stroke in the people involved in the study.

Also, much of the study's data is based on self-reported answers, and some answers may be inaccurate.

Nevertheless, the study provides further support for the well-established notion that lifestyle has a bearing on our cardiovascular health, as well as many other chronic diseases.

While we can't change our genetics or risk factors such as age or gender, this study provides further evidence to support the advice that a healthy diet and active lifestyle, not smoking and limiting alcohol intake give us the best chance of reducing our risk of stroke and other chronic diseases.

Where did the story come from?

The study was carried out by researchers from McMaster University and Hamilton Health Sciences in Canada, and various other global institutions that are part of the INTERSTROKE investigators group.

Funding was provided by several sources, including the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Canada, and the Canadian Stroke Network. 

It was published in the peer-reviewed journal, The Lancet.

Media reports of the study were broadly accurate.

What kind of research was this?

This international case-control study aimed to see which preventable risk factors are associated with stroke.

It compared people from around the world who had and hadn't suffered a stroke to see how they differed on risk factors such as smoking, alcohol or high blood pressure.

As the researchers say, stroke is a leading cause of death and disability, making the condition a global health priority.

This study is the second phase of the INTERSTROKE study. The first phase assessed 6,000 people from 22 countries, and identified 10 preventable risk factors.

This second phase aimed to broaden the sample to include around 27,000 people from 32 countries to further look at how risk factors vary in people from different countries, as well as in those who suffer different types of stroke.

What did the research involve?

From 2007-15, the INTERSTROKE study recruited people from 142 centres in 32 different countries worldwide, including low-income and middle-income countries.

Cases were defined as people who had suffered from their first stroke, recruited within five days of the onset of symptoms and within 72 hours of being admitted to hospital.

All cases had to have had a brain scan and to have met clinical criteria for stroke. They included people with stroke caused by a clot (ischaemic) or by a bleed (haemorrhagic).

Age- and gender-matched controls were recruited from the hospital, such as those admitted or attending outpatients for other reasons, or from the community (recruitment not specified). 

Risk factors were assessed by giving structured questionnaires to cases and controls, which were completed by a friend or relative in just over a third of cases where the person who had a stroke developed difficulties with understanding and communication.

These questionnaires covered:

• history of high blood pressure
• diabetes
• physical activity
• smoking
• alcohol
• psychological stress

Medical records or hospital assessments were used to assess previous heart attack, mechanical valve or heart rhythm problems. Blood samples were also taken to assess proteins that bind to fats (apolipoprotein).

The researchers then compared risk factors between the cases and controls.

What were the basic results?

A total of 26,919 people were recruited from the 32 countries – 13,447 cases with stroke and 13,472 controls.

The researchers identified 10 risk factors that were significantly associated with risk of any stroke.

The following were linked with increased risk:

• high blood pressure (over 140/90mmHg) (odds ratio [OR] 2.98, 95% confidence interval [CI] 2.72 to 3.28)
• current smoking (OR 1.67, 95% CI 1.49 to 1.87)
• high alcohol intake (OR 2.09, 95% CI 1.64 to 2.67)
• high waist-to-hip ratio (OR 1.44, 95% CI 1.27 to 1.64)
• high apolipoproteins B/A1 ratio (OR 1.84, 95% CI 1.65 to 2.06)
• diabetes (OR 1.16, 95% CI 1.05 to 2.30)
• psychosocial factors (INTERHEART stress score) (OR 2.20, 95% CI 1.78 to 2.72)
• heart factors (combined) (OR 3.17, 95% CI 2.68 to 3.75)

A healthy diet and being active were linked with decreased risk:

• high diet modified alternative healthy eating index (mAHEI) score indicating healthier cardiovascular diet (OR 0.60, 95% CI 0.53 to 0.67)
• regular physical activity (OR 0.60, 95% CI 0.52 to 0.70)

When looking at different types of stroke, some factors – such as high blood pressure – were more strongly associated with haemorrhagic stroke, while others – such as smoking, diabetes and blood fats – were more strongly associated with ischaemic stroke.

The researchers calculated that overall, these 10 risk factors could account for 90.7% of all the strokes in the study. That is, if everyone acted on these risk factors, the number of strokes in this sample would plummet by 90%.

How did the researchers interpret the results?

The researchers concluded: "Ten potentially modifiable risk factors are collectively associated with about 90% of stroke in each major region of the world, among ethnic groups, in men and women, and in all ages."

They go on to say their findings "support developing both global and region-specific programmes to prevent stroke".

Conclusion

This valuable research aims to clarify which preventable risk factors are associated with stroke risk – knowledge that could have an effect on addressing this important global health problem.

The study's strengths are that it is based on a large sample size of nearly 27,000 people from 32 countries and of different socioeconomic backgrounds.

The researchers made careful attempts beforehand to calculate how many participants they would need to include to be able to reliably detect differences in risk factors.

There was little missing data across the total sample – for the various different risk factors assessed, only 1% of questionnaires or assessments had missing data.

However, the study has limitations. These include the potential for inaccuracies arising from the self-reported lifestyle and medical questionnaires.

This is particularly a risk for people with stroke for whom the questionnaires were completed by a family member or friend.

Also, certain risk factors, such as past heart attack or problems with heart valves, had to be pooled into one overall category of "heart factors", which makes it difficult to get a reliable indication of what this actually means.

As the researchers also acknowledge, controls may not necessarily be representative of the general population, particularly if most were recruited from hospital departments. The level of recruitment in the community was unclear.

The proportions of strokes that may be attributed to these risk factors are estimates only.

We don't know for definite how much of a contribution they make, and we don't know that these risk factors are the definite cause of stroke in these individuals.

However, the overall finding that medical factors such as high blood pressure, high blood fats and diabetes, and lifestyle factors such as smoking, high alcohol intake, poor diet and low physical activity, are linked with stroke risk is not surprising.

These factors are well known for their association with risk of cardiovascular diseases, as well as certain cancers and other chronic health conditions.  

We may not be able to change our genetics or risk factors such as age or gender, but this study provides further evidence to support advice that we should take care to eat a healthy diet and lead an active lifestyle, avoid smoking and limit our alcohol intake to give us the best chance of reducing our risk of stroke and other long-term diseases.