A recent study found that about half of stroke cases were caused by known risk factors — meaning that the other half of stroke cases were caused by factors not directly associated with risk of stroke.
The researchers determined that high blood pressure and smoking tobacco were the two biggest causes of stroke.
"Ask your doctor how to lower stroke risk."
The lead author of this study was Michiel J. Bos, MD, MSc, from the Department of Epidemiology at Erasmus Medical Center in Rotterdam, The Netherlands.
The study included 6,844 adults aged 55 years and older who enrolled in the Rotterdam Study between 1990 and 1993. The average age of the participants at enrollment was 69 years old, and 60 percent of the participants were women.
None of the participants had a history of stroke at enrollment in the Rotterdam Study.
The current study's researchers looked at medical records to determine history of stroke.
The participants' blood pressure measurements, body measurements, history of smoking tobacco and medical history were also recorded.
The researchers conducted follow-up for an average of 13 years.
The findings showed that 1,020 strokes occurred during 88,011 person-years (number of participants multiplied by number of years in study) of follow-up.
There were 610 ischemic strokes, 103 hemorrhagic strokes and 307 unspecified strokes.
Ischemic strokes happen when the blood flow to the brain is blocked by fatty buildup and/or a blood clot. Hemorrhagic strokes occur when a blood vessel bursts and bleeds into the brain.
High blood pressure and smoking tobacco were the two biggest causes of stroke.
The researchers determined that 36 percent of the stroke cases could have been avoided had the participants not had high blood pressure and 16 percent of cases could have been avoided if the participants didn't smoke tobacco.
Accounting for high blood pressure, smoking tobacco, diabetes, irregular heart beat, coronary heart disease and overweight/obesity, the findings revealed that 51 percent of the stroke cases could have been avoided if the study participants did not have any of these stroke risk factors.
Therefore, almost half of the stroke cases occurred due to reasons other than known stroke risk factors.
The researchers discovered that 55 percent of ischemic strokes could have been avoided if known risk factors were eliminated among the study population.
In addition, 70 percent of hemorrhagic strokes could have been avoided if the participants had not had any stroke risk factors.
"About half of all strokes are attributable to established causal and modifiable factors. This finding encourages not only intervention on established [causative] factors, but also further study of less well established factors," Dr. Bos and team concluded.
This study was limited because most of the study participants were Caucasian and from middle and high-income areas. In addition, the study participants were likely more aware of risk factors than the general population.
This study was published on April 29 in PLOS Medicine.
This research was funded by Erasmus Medical Center Rotterdam, the Erasmus University Rotterdam, the Netherlands Organization for Science Research, the Netherlands Organization for Health Research and Development, the Research Institute for Diseases in the Elderly, the Ministry of Education, Culture and Science, the Ministry of Health, Welfare and Sports, the European Commission and the Municipality of Rotterdam.