‘Hypertension, physical inactivity cause 83.7% of stroke’

• Global study identifies 10 modifiable risk factors
• Alcohol intake was highest in Africa, south Asia

Scientists have confirmed hypertension and physical inactivity as the two major causes of stroke, constituting 83.7 per cent of the burden. They also identified eight other modifiable risk factors.

According to an analysis of nearly 27,000 people from every continent in the world published over the weekend in The Lancet, the other risk factors for stroke are: poor diet, obesity, smoking, cardiac (heart) causes, diabetes, alcohol intake, stress, and lipids.

The study used apolipoproteins, which was found to be a better predictor of stroke than total cholesterol.

Apolipoproteins are proteins that bind lipids to form lipoproteins and transport the lipids through the lymphatic and circulatory systems. The lipid components of lipoproteins are insoluble in water.

To estimate the proportion of strokes caused by specific risk factors, the investigators calculated the population attributable risk (PAR) for each factor, an estimate of the overall disease burden that could be reduced if an individual risk factor were eliminated.

According to the study, the PAR was 47.9 per cent for hypertension, 35.8 per cent for physical inactivity, 23.2 per cent for poor diet, 18.6 per cent for obesity, 12.4 per cent for smoking, 9.1 per cent for cardiac (heart) causes, 3.9 per cent for diabetes, 5.8 per cent for alcohol intake, 5.8 per cent for stress, and 26.8 per cent for lipids.

The researchers noted that many of the risk factors are known to also be associated with each other, like obesity and diabetes and when combined together, the total PAR for all 10 risk factors was 90.7 per cent, which was similar in all regions, age groups and in men and women.

The authors said: “Hypertension (high blood pressure) remains the single most important modifiable risk factor for stroke, and the impact of hypertension and nine other risk factors together account for 90 per cent of all strokes.

Although the same 10 risk factors were important, and together accounted for 90 per cent of stroke risk in all regions, the relative role of some individual risk factors varied by region, which should influence the development of strategies for reducing stroke risk.”

They said 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 per cent of strokes, and haemorrhagic stroke -bleeding in the brain- which accounts for 15 per cent.

Prevention of stroke is a major public health priority, but needs to be based on a clear understanding of the key preventable causes of stroke.

The study led by Dr. Martin O’Donnell of the Population Health Research Institute at McMaster University, Hamilton, Ontario, Canada and the HRB-Clinical Research Facility, NUI Galway, Ireland, and Prof Salim Yusuf, Population Health Research Institute at McMaster University, along with collaborators from 32 countries, builds on preliminary findings from the first phase of the Ischaemic and Intercerebral Haemmorhage Stroke (INTERSTROKE) study, which identified 10 modifiable risk factors for stroke in 6000 participants from 22 countries.

The full-scale INTERSTROKE study included an additional 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.

O’Donnell said: “This study is of an adequate size and scope to explore stroke risk factors in all major regions of the world, within key populations and within stroke subtypes. The wider reach confirms the ten modifiable risk factors associated with 90 per cent of stroke cases in all regions, young and older and in men and women. The study confirms that hypertension is the most important modifiable risk factor in all regions, and the key target in reducing the burden of stroke globally.”

Prof Salim Yusuf said: “This is the first study that is adequately powered to explore stroke risk factors in all regions of the world and between stroke subtypes. The wider scope of this phase of our study lends a greater generalisability to the original INTERSTROKE results, and confirms the ten modifiable risk factors associated with 90 per cent of stroke cases. The study also confirms that hypertension is the most important modifiable risk factor in all regions, and is therefore the key target in reducing the burden of stroke globally.”

Writing in a linked comment, Professor Valery L. Feigin and Dr. Rita Krishnamurthi from the National Institute for Stroke and Applied Neurosciences, Faculty of Health and Environmental Sciences, University of Technology, Auckland, New Zealand, said: “Three key messages can be drawn from this study.

First, stroke is a highly preventable disease globally, irrespective of age and sex. Second, the relative importance of modifiable risk factors and their PAR necessitates the development of regional or ethnic-specific primary prevention programmes, including priority settings such as focusing on risk factors contributing most to the risk of stroke in a particular region (as determined by PAR).

“Third, additional research on stroke risk factors is needed for countries and ethnic groups not included in INTERSTROKE, as well as definitive cost-effectiveness research on primary stroke prevention in key populations (example, different age, sex, ethnicity, or region). It should also be emphasised that stroke prevention programmes must be integrated with prevention of other major non-communicable diseases that share common risk factors with stroke to be cost-effective…We have heard the calls for actions about primary prevention. Now is the time for governments, health organisations, and individuals to proactively reduce the global burden of stroke.”