Though the chances of a stroke jump dramatically with age, the growing number of younger people with worrying risk factors such as bulging waistlines, diabetes and high blood pressure means they are becoming increasingly susceptible.
Worldwide, stroke is the second-leading cause of death after heart disease and is also a big contributor to disability.
Most strokes occur when a clot blocks the blood supply to the brain. Patients often experience symptoms including a droopy face, the inability to lift their arms and garbled speech. If not treated quickly, patients can be left with long-term side effects, including speech and memory problems, paralysis and the loss of some vision.
Scientists combed through more than 100 studies from 1990 to 2010 studying stroke patients across the world and also used modeling techniques when there wasn't enough data. They found the incidence of stroke has jumped by a quarter in people aged 20 to 64 and that those patients make up almost one-third of the total number of strokes.
Researchers said most strokes still occur in the elderly and that the numbers of people suffering strokes are still increasing as the world's population ages.
"Some of the increase we will see in strokes is unavoidable because it has to do with people aging, but that doesn't mean we should give up," said Majid Ezzati of Imperial College London, one of the study's authors. Ezzati said countries should focus on reducing smoking rates further, aggressively controlling blood pressure and improving eating habits.
Ezzati said developing countries such as Iran and South Africa that have set up national systems to monitor maternal and child health are a good model for similar initiatives that could help keep stroke risk factors, such as high blood pressure, in check.
Ezzati and colleagues found the death rate from strokes dropped 37 percent in developed countries and 20 percent in developing countries, largely because of better diagnosis and treatment.
Stroke prevalence was highest in East Asia, North America, Europe and Australia. It was lowest in Africa and the Middle East -though researchers said people in those regions may be dying of other ailments before they get old enough to have a stroke.
In the U.S., doctors have already noted an alarming increase in strokes among young and middle-aged Americans, while the number has been dropping in older people.
The research was paid for by the Bill & Melinda Gates Foundation and published online Thursday in the journal Lancet.
"Young people think stroke is only a problem of the elderly, but we need to educate them," said Dr. Yannick Bejot of the University Hospital of Dijon in France, who co-wrote an accompanying commentary. He added that using illegal drugs such as marijuana and cocaine also boosts the chance of a stroke.
"If young people understood how debilitating a stroke is, maybe they would change their behavior," he said.
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