Managing certain factors can reduce your risk of stroke and stroke severity. (Basicdog/Shutterstock)
In a nutshell
- Three risk factors—high blood pressure, atrial fibrillation, and smoking—are more likely to cause severe strokes, meaning strokes that result in death or long-term disability.
- People with these conditions weren’t just more likely to have a stroke; they were significantly more likely to have a catastrophic one. For example, atrial fibrillation raised the odds of a severe stroke by nearly five times.
- Regions like South Asia and Africa had the highest rates of severe stroke, highlighting global health disparities and the urgent need for better prevention strategies, especially in lower-income countries.
MINNEAPOLIS — If you have high blood pressure, an irregular heartbeat, or smoke cigarettes, you’re not just at risk for having a stroke. According to a new international study, these factors also might make you more likely to have a catastrophic one that could leave you severely disabled or dead.
The study, published in the journal Neurology, revealed that certain vascular risk factors aren’t created equal when it comes to stroke severity. While all known risk factors can lead to stroke, three particular threats—hypertension, atrial fibrillation, and smoking—are significantly more likely to cause strokes that devastate a person’s independence and quality of life.
“Stroke can lead to disability or even death, yet there are a number of risk factors that people can modify with a change in lifestyle or medication,” says study author Catriona Reddin from the University of Galway, in a statement. “Our results emphasize the importance of managing risk factors for stroke, especially high blood pressure, atrial fibrillation, and smoking in order to prevent severe, disabling stroke.”
Risk Factors That Make Strokes More Severe
Not all strokes are equally devastating. Some people recover with minimal disability, while others are left permanently dependent on caregivers or don’t survive. Understanding which risk factors lead to the most disabling outcomes could help shape more targeted prevention strategies worldwide.
The research team analyzed data from 13,460 stroke patients and 13,488 matched controls. They classified strokes as “severe” if patients scored 4-6 on the modified Rankin Scale (mRS), which indicates patients unable to walk without assistance, requiring constant nursing care, or deceased. Non-severe strokes (scores 0-3) included patients with no symptoms to moderate disability but still able to walk independently.
People with high blood pressure had 3.2 times higher odds of severe stroke compared to 2.9 times higher odds of non-severe stroke than people without high blood pressure. The disparity was even more dramatic with atrial fibrillation, an irregular heart rhythm that can cause blood clots, where patients had 4.7 times higher odds of severe stroke versus 3.6 times higher odds of non-severe stroke than people without this condition. Smokers showed a similar pattern, with 1.9 times higher odds of severe stroke compared to 1.7 times higher odds of non-severe stroke than non-smokers.
A total of 74% of those with severe stroke had high blood pressure, compared to 72% of those with mild to moderate stroke. For atrial fibrillation, 11% of those with severe stroke had the condition, compared to 9% of those with mild to moderate stroke. In both severity groups, 30% were current smokers.
One physical characteristic bucked this trend. People with high waist-to-hip ratios (excess fat around the midsection) had stronger associations with non-severe strokes than severe ones. This might mean that where your body stores fat, like around the belly, can affect how a stroke plays out.
Stroke Disparities
Around the world, severe stroke risk shifts by location. South Asia and Africa had the highest proportions of severe strokes (57.3% and 53.9%, respectively), while Western Europe, North America, and Australia had the lowest (18.2%). This could be due to gaps in preventive care and early intervention in lower and middle-income regions.
“Our findings emphasize the importance of controlling high blood pressure, which is the most important modifiable risk factor for stroke globally,” says Reddin. “This is particularly relevant for lower- and middle-income countries that have rapidly increasing rates of high blood pressure and strokes at younger ages.”
The type of stroke also played a major role in severity. Hemorrhagic strokes (bleeding in the brain) were far more likely to be severe than ischemic strokes (caused by blood clots). Among patients with severe strokes, 35.7% had hemorrhagic strokes compared to just 15.4% of those with non-severe strokes.
For ischemic strokes, location mattered enormously. Three-quarters of patients with clots affecting the “total anterior circulation,” a large portion of the brain, experienced severe outcomes. This helps explain why atrial fibrillation, which tends to cause larger clots, is associated with more devastating strokes.
By controlling for age and other variables, researchers could isolate the independent effects of each risk factor. Previous studies had shown atrial fibrillation was linked to worse strokes, but this was often attributed to the fact that patients with this condition were typically a decade older. The new research confirms that even when accounting for age, these risk factors independently predict more severe outcomes.
Preventing hypertension, atrial fibrillation, and smoking doesn’t just reduce stroke risk; it specifically reduces the risk of the most devastating strokes. These findings could translate directly to saved lives and preserved independence for millions. Stroke remains a leading preventable cause of disability worldwide, and understanding which factors most influence severity is a powerful new tool in fighting its worst outcomes.
Paper Summary
Methodology
The INTERSTROKE study is an international case-control study examining risk factors for first acute stroke across 32 countries. Researchers enrolled 13,460 patients with first acute stroke (cases) and 13,488 matched controls between 2007 and 2015. Stroke severity was measured using the modified Rankin Scale (mRS) within 72 hours of hospital admission, with severe stroke defined as mRS scores of 4-6 (unable to walk independently, requiring constant nursing care, or dead) and non-severe stroke as scores of 0-3. The researchers used multinomial logistic regression to estimate comparative odds ratios for severe versus non-severe stroke, and conducted a matched case-case analysis (matching for age, sex, country, and stroke type) to determine whether risk factor prevalence differed between severity groups.
Results
Of the stroke patients studied, 64% had non-severe strokes and 36% had severe strokes. Three risk factors showed significantly stronger associations with severe stroke: hypertension (OR 3.21 for severe vs 2.87 for non-severe), atrial fibrillation (OR 4.70 for severe vs 3.61 for non-severe), and smoking (OR 1.87 for severe vs 1.65 for non-severe). Conversely, high waist-to-hip ratio had a stronger association with non-severe stroke. Geographically, severe strokes were most prevalent in South Asia (57.3%) and Africa (53.9%), with the lowest rates in Western Europe/North America/Australasia (18.2%). Hemorrhagic strokes were more likely to be severe (35.7% of severe strokes vs 15.4% of non-severe strokes), and among ischemic strokes, those affecting the total anterior circulation were most often severe.
Limitations
The study authors acknowledge potential influence from unmeasured confounders. The case-control design presents inherent limitations, including challenges with obtaining representative samples across the stroke spectrum, particularly with severe stroke patients who may have difficulty communicating. Using the mRS to measure stroke severity rather than a neurologic scale might be influenced by other comorbidities and frailty that affect mobility but are not directly stroke-related. Additionally, the mRS may underestimate severity in patients whose mobility remains unaffected.
Funding and Disclosures
The INTERSTROKE study was funded by multiple organizations including the Canadian Institutes of Health Research, Heart and Stroke Foundation of Canada, Canadian Stroke Network, Swedish Research Council, Swedish Heart and Lung Foundation, and through unrestricted grants from pharmaceutical companies including AstraZeneca, Boehringer Ingelheim, Pfizer, and MSD. Additional support came from Chest, Heart and Stroke Scotland, the Stroke Association, and the UK Stroke Research Network. The lead author, Dr. Reddin, was supported by the Irish Clinical Academic Training Programme, the Wellcome Trust, and the Health Research Board.
Publication Information
The paper “Association of Vascular Risk With Severe vs Non-Severe Stroke: An Analysis of the INTERSTROKE Study” was published in the journal Neurology (Volume 103, Number 11, December 10, 2024). It was authored by Catriona Reddin and colleagues from multiple international institutions, including the University of Galway, Ireland; the University of Western Australia; Rush University Medical Center, USA; and numerous other research centers worldwide.
