Collaborators from 32 countries, build on preliminary findings from the first phase of the INTERSTROKE study, which identified ten modifiable risk factors for stroke in 6000 participants from 22 countries.
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 percent of all strokes, according to an analysis of nearly 27,000 people from every continent in the world (INTERSTROKE).
To estimate the proportion of strokes caused by specific risk factors, the investigators calculated the population attributable risk (PAR) for each factor. The PAR, which is an estimate of the overall disease burden that could be reduced if an individual risk factor were eliminated, was 47.9 percent for hypertension, 35.8 percent for physical inactivity, 23.2 percent for poor diet, 18.6 percent for obesity, 12.4 percent for smoking, 9.1 percent for cardiac (heart) causes, 3.9 percent for diabetes, 5.8 percent for alcohol intake, 5.8 percent for stress, and 26.8 percent for lipids.
Many of these risk factors are known to also be associated with each other (e.g. obesity and diabetes), and when combined together, the total PAR for all ten risk factors was 90.7 percent, which was similar in all regions, age groups and in men and women.
Interestingly, the importance of some risk factors appeared to vary by region. For example, the PAR for hypertension ranged from 38.8 percent in western Europe, North America and Australia to 59.6 percent in Southeast Asia, the PAR for alcohol intake was lowest in western Europe, North America, Australia and highest in Africa (10.4 percent) and south Asia (10.7 percent), while the PAR for physical inactivity was highest in China.
Atrial fibrillation (irregular heart rhythm) was significantly associated with ischaemic stroke (PAR ranging from 3.1 percent in south Asia to 17.1 percent in western Europe, North America, and Australia), as was a high apolipoprotein [ApoB]/A1 ratio (PAR ranging from 24.8 percent in western Europe, North America, and Australia to 67.6 percent in southeast Asia).
Researchers said, “Our findings will inform the development of global population-level interventions to reduce stroke, and how such programmes may be tailored to individual regions, as we did observe some regional differences in the importance of some risk factors by region. This includes better health education, more affordable healthy food, avoidance of tobacco and more affordable medication for hypertension and dyslipidaemia.”
The National Institute for Stroke and Applied Neurosciences 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 (eg, 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.