TUESDAY, April 10, 2012 (HealthDay News) -- One clue to your risk for a stroke may come from a look at your siblings' experience with the brain attacks, a new study says.
People whose brother or sister had a stroke were up to 64 percent more likely to suffer one, compared to folks without such family histories, Swedish researchers report.
The risk rose even higher when the stroke to the sibling occurred when he or she was relatively young. For example, when a sibling had a stroke before the age of 56, their brother or sister's risk for a stroke nearly doubled, the study found.
The findings refer to the most common kind of stroke -- so-called ischemic stroke -- which occurs when blood flow is cut off to the brain as a result of a blood-vessel blockage.
"Patients in the risk zone of getting a heart attack or a stroke should be made aware that a genetic predisposition exists," said study lead author Dr. Erik Ingelsson, a professor of cardiovascular epidemiology at the Karolinska Institute, in Stockholm.
Still, that does not mean that you're doomed to suffer a stroke if your sibling did, Ingelsson added. "The increased familial risk may not solely be due to genetics," he said. "Similar lifestyle within families could also be involved -- and lifestyle can of course be modified."
The findings are published April 10 in Circulation: Cardiovascular Genetics.
Roughly 700,000 Americans experience an ischemic stroke every year, according to the American Heart Association.
To get a handle on sibling-associated stroke risk, the Swedish team pored through Swedish hospital discharge data and death registries for the period between 1987 and 2007.
The information included more than 30,700 men and women whose siblings had experienced a stroke, as well as another roughly 152,000 adults with no history of sibling stroke.
The results: Those whose brother or sister had had a stroke were between 61 and 64 percent more likely than those with no such family history to have one themselves.
Those whose half-brother or half-sister had had a stroke faced a 41 percent greater chance of having a stroke.
And those whose siblings had a stroke at the age of 55 or younger faced a 94 percent bump in their own stroke risk -- a nearly doubling of risk.
Gender did not appear to play a role in the degree to which sibling stroke history affected one's own risk.
The study authors stressed that they only looked at stroke incidence and did not explore family histories for any underlying risk factors, such as high blood pressure or cholesterol levels. That means they could not break down the degree to which genetic factors influenced stroke risk, versus the role played by nurture -- a shared upbringing.
However, "if your sibling has had a stroke, it may be a good idea to pay more attention to lifestyle habits such as diet and exercise, and to have your blood pressure checked at regular intervals," Ingelsson advised.
Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, said the study was "helpful" in better understanding stroke risk.
"This gives us insight into family risk, which involves both genetics, in terms of high blood pressure and high cholesterol risk, as well as a history of shared lifestyles," he said.
"Clearly, those with a first-degree relative who has had a stroke earlier in life are at much higher risk themselves, and should be seeking to address all the modifiable risk factors for a stroke," Fonarow added.
Dr. Murray Mittleman, director of the cardiovascular epidemiology research unit at Beth Israel Deaconess Medical Center in Boston, said: "Although you can't control your and your sibling's past history, you can control your current risk through lifestyle interventions.
"That would mean quitting smoking if you're a smoker," he said. "Getting your blood pressure checked and controlling it with medications so it's at a safe level. Maintaining an active lifestyle. And eating a heart-healthy diet with a good balance of healthy fats, fresh fruits and vegetables, and a reasonable amount of fiber."
Find out more about stroke at the National Stroke Association.