The observational study involved 5,600 men and women over age 65 who were free of stroke when they started the study. The participants were followed for four to eight years to record the number and type of strokes that occurred.

The people with the lowest amount of potassium in their diet were 1.5 times more likely to have a stroke than those with the highest amount of potassium in their diet. Low potassium intake was defined as less than 2.4 grams per day; high intake was more than four grams per day.

Researchers say that more studies are needed confirm these results and to determine whether increasing potassium in the diet can prevent strokes.

Other studies have shown that low amounts of potassium in the diet are associated with a greater risk of death from stroke. The study also looked at people taking diuretics, common medications that reduce the amount of water in the body and can rob potassium from the body. Diuretics are used to treat conditions such as high blood pressure, congestive heart failure and kidney disease.

"Diuretics clearly help prevent stroke by controlling high blood pressure, but we wanted to see whether their effect on potassium levels would affect the risk of stroke," said study author and neurologist Deborah M. Green, MD, of the Neuroscience Institute at The Queen's Medical Center in Honolulu, Hawaii.

Of people taking diuretics, the study found that those with the lowest level of potassium in their blood were 2.5 times more likely to have a stroke than those with the highest level of potassium in their blood.

Green stressed that the results do not imply that diuretics create an excessive risk of stroke. "The question is whether diuretics would be even more effective with adequate potassium intake," she said.

That question may be especially important for people with many other risk factors for stroke, such as diabetes, atrial fibrillation and cigarette smoking, according to neurologist Steven R. Levine, MD, of The Mount Sinai School of Medicine in New York, NY, a stroke expert who wrote an editorial accompanying the study along with neurologist Bruce Coull, MD, a stroke expert with the University of Arizona Health Science Center in Tucson.

"Even a slightly increased risk added to other risks could have a large effect," he said. "But overall, despite this potential adverse effect, evidence shows that low-dose diuretics are highly effective anti-high blood pressure therapies for preventing both stroke and heart disease."

Researchers also examined the small number of diuretic users who also had atrial fibrillation, an irregular heart rhythm that increases the risk of stroke. They found that those with atrial fibrillation and low blood potassium were 10 times more likely to develop a stroke than diuretic users with regular heart rhythms and higher blood potassium levels.

The study is part of the Cardiovascular Health Study, which involves 5,888 people from four communities: Forsyth County, North Carolina; Sacramento County, California; Washington County, Maryland; and Allegheny County, Pennsylvania. Good sources of potassium include avocados, bananas, citrus fruits, green leafy vegetables, milk and nuts.

The study was supported in part by contracts with the National Heart, Lung, and Blood Institute.