Diets high in potassium and magnesium may lower the risk of stroke for men, especially those with high blood pressure, according to a report released yesterday by doctors at the School of Public Health.

The study, published in the medical journal Circulation, was started by Dr. Walter C. Willett, Stare professor of epidemiology and nutrition, and lasted from 1986 until 1994. More than 40,000 male volunteers from the healthcare industry participated in the study.

When these men joined the study in 1986, each was classified according to how much potassium he consumed on a daily basis.

Over the following eight years, 300 of these men, aged 40 to 75, suffered strokes. The group with the highest potassium intake had a 38 percent lower chance of suffering a stroke, according to the study. In addition, those with the highest magnesium intake had a chance of a stroke 30 percent lower than those who had the least magnesium.

Dr. Alberto Ascherio, assistant professor of nutrition and epidemiology, the primary author of the report, said this study shed new light on the importance of diet. In the past, diet was connected to heart disease, but not strokes.

"More studies have been done on heart disease than strokes. The risk of stroke can be reduced by a good diet--by eating more fruits and vegetables," Ascherio said.

This is not the only Harvard study to come out this year on the relationship between strokes and potassium. Dr. Frank M. Sacks, associate professor of nutrition, published a report in the January issue of Hypertension, which said potassium could lower high blood pressure, the leading cause of strokes. His study did not concern magnesium.

Sacks said it was difficult to separate the effects of potassium and magnesium.

"Foods that contain potassium often contain magnesium as well," he said.

This makes it difficult to determine whether or not magnesium is actually a factor.

However, Sacks said he was sure that potassium played a part in lowering blood pressure.

"It was the potassium which lowered blood pressure," he said.

High levels of potassium and magnesium are found in foods such as bananas, Brussels sprouts, and orange juice. Most fruits and vegetables contain some potassium and magnesium. Nine servings of fruits and vegetables a day is considered to be a large potassium intake.

The more recent study also found that men taking potassium supplements showed a 60 percent lower chance of stroke than men with high blood pressure who were not taking the supplements.

However, Ascherio cautioned against taking supplements. He instead recommended eating more fruits and vegetables, since they contain other beneficial nutrients, and potassium may not be the only substance that helps to reduce stroke risk. High levels of potassium can also be harmful to those with kidney problems.