Study Identifies 10 Risk Factors Associated With 90% of the Risk of Stroke

Study Identifies 10 Risk Factors Associated With 90% of the Risk of Stroke
NEW YORK -- June 18, 2010 -- A study published early online and appearing in an upcoming edition of The Lancet shows that a total of 10 risk factors are associated with 90% of the risk of stroke.

Results of the study are published online first and in an upcoming edition of The Lancet and will be presented at the World Congress of Cardiology in Beijing, China.

The contribution of various risk factors to the burden of stroke worldwide is unknown, particularly in countries of low and middle income where the largest burden of stroke occurs.

In the first phase of the INTERSTROKE study, Martin J O'Donnell, MD, and Salim Yusuf, MD, McMaster University, Hamilton, Ontario, and colleagues aimed to establish the association of known and emerging risk factors with stroke and its primary subtypes, assess the contribution of these risk factors to the burden of stroke, and explore the differences between risk factors for stroke and MI.

The authors used data from 6,000 people (3,000 cases of stroke and 3,000 controls) in 22 countries worldwide, covering the period March 2007 to April 2010. Cases were patients with a first acute stroke (within 5 days of symptoms onset and 72 hours of hospital admission). Controls had no history of stroke, and were matched with cases for age and sex.

All participants completed a structured questionnaire and a physical examination, and most provided blood and urine samples.

The researchers calculated the increased risk and population-attributable risks (PARs) for the association of all stroke, ischaemic stroke, and intracerebral haemorrhagic stroke with selected risk factors.

The authors found the following 10 risk factors to be significantly associated with stroke: high blood pressure, smoking, waist-to-hip ratio, diet, physical activity, lipids, diabetes mellitus, alcohol intake, stress and depression, and heart disorders.

Collectively, these risk factors accounted for 90% of the PAR for all stroke. These risk factors were all significant for ischaemic stroke, whereas hypertension, smoking, waist-to-hip ratio, diet, and alcohol intake were significant risk factors for intracerebral haemorrhagic stroke. The ratio of bad to good apolipoproteins was an important risk factor for ischaemic stroke but not for haemorrhagic stroke.

When looking at individual risk factors, the authors said it is important to note that the individual PARs for risk factors do not add up to the overall PAR for all risk factors combined. This is because many risk factors are inter-related. The study also addressed each risk factor independently, and found that high blood pressure was the most important for stroke, since it was associated with one-third of the risk of all stroke, and increased the risk of stroke more than 2.5-fold compared with no history of high blood pressure. Smokers were at double the risk of stroke compared with non-smokers, and smoking was associated with 1 in 5 strokes.

"The INTERSTROKE study is the first large standardised case-control study of risk factors for stroke in which countries of low and middle income were included, and where all cases completed a brain scan," the authors wrote. "Our findings showed that 5 risk factors accounted for more than 80% of the global risk of all stroke (ischaemic and intracerebral haemorrhagic): hypertension, current smoking, abdominal obesity, diet, and physical activity. With the addition of 5 other risk factors, including apolipoproteins, the PAR for all stroke rose to 90%."

The authors highlighted that 9 of 10 risk factors (not including cardiac disorders) in INTERSTROKE are the same as in INTERHEART study which looked at risk factors for MIs. The relative importance of many of these risk factors is different for stroke and MI. For example, blood pressure is the most important risk factor for stroke, while blood lipids are the most important risk factors for MI. However, the 9 risk factors in INTERHEART covered 90% of the PAR for MIs.

In an accompanying comment, Jack V. Tu, MD, Institute for Clinical Evaluative Sciences, Sunnybrook Schulich Heart Centre, University of Toronto, Toronto, Ontario, said: "Whilst hypertension is well established as the most important cause of stroke in high-income countries, INTERSTROKE confirms that it is also the most important risk factor for stroke in developing countries. This finding is particularly relevant because it highlights the need for health authorities in these regions to develop strategies to screen the general population for high blood pressure and, if necessary, offer affordable treatment to reduce the burden of stroke. It also provides an impetus to develop population-wide strategies to reduce the salt content in the diet of individuals in these countries."

SOURCE: The Lancet