by Kristina Fiore
There are 10 factors that appear to make up the vast majority of stroke risk, and half of those are modifiable, a large population study found.
Hypertension appears to be the strongest predictor of stroke, along with smoking, abdominal obesity, diet, and physical activity, according to Martin J. O’Donnell, MB, PhD, of McMaster University in Hamilton in Ontario, Canada.
“This is good news in the sense that the causes of stroke are potentially modifiable, but that’s not going to be realized unless strategies are implemented and taken up,” O’Donnell said in an interview with MedPage Today.
The results are from the INTERSTROKE study, a large, multicenter, case-control study that included patients from low- and middle-income countries, published online June 18 in The Lancet.
The same group of researchers had also conducted INTERHEART, which concluded that there were nine risk factors for myocardial infarction: hypertension, smoking, abdominal obesity, diet, physical activity, diabetes, alcohol, psychosocial factors, and cholesterol.
In the first phase of INTERSTROKE, the researchers included 3,000 cases and 3,000 controls from 22 countries between March 1, 2007, to April 23, 2010.
More of the cases had ischemic stroke than intracerebral hemorrhagic stroke (78% versus 22%).
The researchers found that a history of hypertension was the strongest risk factor for stroke, with nearly a threefold increased risk (OR 2.64, 95% CI 2.26 to 3.08), and the association was stronger for hemorrhagic stroke.
“Hypertension is completely modifiable, as it is regularly treated with inexpensive generic medications,” O’Donnell said.
Yet he acknowledged that there are several factors that stand in the way of hypertension reduction.
“We know we have a problem with suboptimal levels of screening for hypertension, and once a patient is diagnosed with hypertension, a large portion are not treated to target guidelines,” he said. “That’s not a physician problem, or a patient problem, it’s a combined problem.”
He said he hopes the study will motivate patients to get their blood pressure checked, and physicians to monitor blood pressure and treat to guidelines.
On a population level, he said sodium reduction is key.
“Although most people have firmed up in their head the importance of salt reduction, the real target population are those who consume excess salt,” he added. “They’re the low-lying fruit and the most important target population.”
Yet researchers expressed concern that the new USDA guidelines, released last week, sought to reduce salt consumption to 1,500 mg per day and warned that many people haven’t achieved the daily 2,300 mg limit set by the previous guidelines. (See: New Diet Guidelines Focus on Unhealthy Population)
Smoking status was also a key risk factor for stroke, with about a twofold increased risk (OR 2.09, 95% CI 1.75 to 2.51), and an even stronger association for ischemic than hemorrhagic stroke. Risk also increased with the number of cigarettes smoked per day, the researchers said.
Interestingly, there was a reduced risk of stroke associated with former smoking, compared with never smoking (OR 0.74, 95% CI 0.57 to 0.95).
O’Donnell and colleagues noted that even if the finding for former smoker “isn’t real,” it suggests that “risk rapidly reduces after stopping smoking, indicating that smoking cessation is an essential component for any stroke prevention program.”
Body mass index wasn’t associated with stroke, but waist-to-hip ratio was, with an increased relative risk of 65% (95% CI 1.36 to 1.99).
A history of diabetes carried a 36% increased risk of stroke overall, although it wasn’t associated with an increased risk of hemorrhagic stroke.
Stress and depression also appeared to be risk factors (30% and 35% increased risk, respectively), but depression, like diabetes, wasn’t associated with an increased risk of hemorrhagic stroke.
Atrial fibrillation was the most common cardiac source of thromboembolism in ischemic stroke, but overall there was a relatively low prevalence of cardiac causes of stroke — especially in India and China, the researchers said.
However, this may reflect lower rates of cardiac diagnostic testing.
Total cholesterol was only associated with an increased risk of hemorrhagic stroke. Having more HDL, or “good” cholesterol, appeared to be protective against ischemic stroke, but not hemorrhagic stroke.
More importantly, the ratio of apolipoproteins B to A1 was associated with an 89% increase in stroke risk (95% CI 82.3 to 92.2).
A good diet along with regular physical activity and moderate alcohol intake were protective against stroke.
Fruits and fish were especially protective (OR 0.61, 95% CI 0.50 to 0.73 and OR 0.78, 95% CI 0.66 to 0.91, respectively) but vegetables were not. The researchers said this relationship needs further exploration.
Eating more red meat, organ meats, or eggs came with a 35% increased risk of stroke (95% CI 1.10 to 1.65), more fried foods, pizza, or salty snacks carried a 16% increased risk, (95% CI 0.99 to 1.37) and cooking with lard made stroke risk rocket to 66% (95% CI 1.06 to 2.60).
Exercising was associated with more than a 30% reduction in stroke risk.
While moderate alcohol intake was protective, having more than 30 drinks per month carried about a 50% higher stroke risk.
O’Donnell said that just five of these risk factors account for more than 80% of the overall risk of stroke: hypertension, smoking, abdominal obesity, diet, and physical activity. Adding the other five brings that figure to 90%.
O’Donnell added that there’s “contention” as to what might comprise that additional 10% of risk.
“Certainly one of the issues might be whether there’s room for [one of the risk factors] to be more important,” he said. “Or there may be a genetic contribution, which can take two forms. One is that it has a direct risk factor. Or you can have a genetic vulnerability to a risk factor.”
For example, some patients may be particularly susceptible to the effects of blood pressure or cholesterol, he said.
O’Donnell added that genetics will be a key focus of the second phase of INTERSTROKE.
The study was limited by its case-control design, which left room for selection bias and recall bias. But researchers appear hopeful about its take-home messages.
Roger Bonomo, MD, director of stroke care at Lenox Hill Hospital in New York, called it notable that “the risk factors identified in the low- and middle-income populations studied are the same as those found in the upper economic populations.”
“The differences between such populations will be found in the availability of resources to reduce such risks by treating hypertension, encouraging smoking cessation, and modifying diet and exercise practices,” he added.
In an accompanying commentary, Jack V. Tu, MD, of the University of Toronto, acknowledged the same issue. He said 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.”
He added that it also “reinforces the need to reduce the high smoking rates in countries such as China and India through tough antismoking policies,” concluding that “these important findings should help to inform stroke prevention strategies around the world and to reduce the global burden of stroke.”
Kristina Fiore is a MedPage Today staff writer.