Good sources of potassium include bananas and other fruits and vegetables, as well as fish, poultry and dairy, the researchers noted.
And ounce per ounce, sweet potato and tomato paste top the list, according to the U.S. Department of Agriculture.
"The average dietary potassium intake in most countries worldwide is much lower than recommended by health authorities, and increasing potassium intake may provide protection against stroke and other cardiovascular disorders," said lead researcher Dr. Pasquale Strazzullo, a professor of medicine at the Federico II University of Naples Medical School, in Italy.
The report is published in the March 1 online edition of the Journal of the American College of Cardiology.
For the study, Strazzullo's team pulled data about potassium and cardiovascular disease from 11 studies, which included a total of 247,510 men and women. The researchers looked at what people in these studies recalled eating in the past day.
This process is called a meta-analysis, in which researchers look for trends in the data that may support a particular conclusion, even when these data were not the main point of the study.
They found that people who consumed 1.64 grams of potassium or more a day had a 21% lower risk of stroke and also tended to have a lower risk of any cardiovascular disease.
Strazzullo noted that five or more servings of fruits and vegetables will provide the amount of potassium needed to get this protective effect.
"The protective effect of potassium against the risk of stroke and other vascular events may in part be traced to its blood pressure-lowering effect, particularly in hypertensive individuals and in those with elevated sodium intake," Strazzullo said.
However, other processes appear to be at work as well, he added. For example, potassium may be involved in slowing the process of atherosclerosis and preventing the thickening of the walls of arteries, all of which can lead to cardiovascular disease.
"More recently, a high-potassium diet was shown to exert a protective effect against the development of vascular damage induced by excess salt intake, thus counteracting, to some extent, the dangerous effects of eating too much salt. This large body of evidence from experimental studies provides biological plausibility to the protective effect of dietary potassium against cardiovascular events," Strazzullo said.
A higher potassium intake is safe for most people, Strazzullo said, adding that there might be some concern about elevated potassium for patients with kidney failure or those taking medicines that lower potassium. In those cases, patients should speak with their doctors, he added.
Dr. Larry B. Goldstein, director of the Duke Stroke Center at Duke University Medical Center, commented that "this is completely consistent with current American Heart Association dietary recommendations."
The best example is the DASH-type eating plan, which has been tested in various studies, he said.
"The DASH diet is rich in fruits and vegetables and nuts, moderate in low-fat dairy products, low in sodium and high in potassium. The effect on stroke is likely mediated, at least in part, through lower blood pressure," Goldstein said.
Another expert, Dr. Gregg Fonarow, spokesman for the American Heart Association and professor of cardiology at the University of California, Los Angeles, added that "clinical trials have established that a diet high in potassium and low in sodium can significantly lower blood pressure."
Because high blood pressure is one of the major risk factors for heart disease and stroke, it follows that higher-potassium diets would be linked to lower risk of stroke and heart attacks, he said.
"However, a higher-potassium diet potentially has other mechanisms of benefit, including protecting blood vessels from oxidative damage and limiting thickening of the blood vessel wall," Fonarow said.
Increasing potassium in the diet while limiting sodium may help to reduce the risk of stroke and confer other cardiovascular benefits, he said. "Fruits such as bananas, cantaloupe, grapefruit, oranges, vegetables like tomatoes and low-fat dairy products are a good source of dietary potassium," he said.
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