High doses of fish oil appear to lower high blood pressure, possibly offering a way to decrease the risk of suffering a heart attack and stroke for 60 million Americans, researchers reported Wednesday.

The researchers cautioned, however, against taking high doses of fish oil to treat high blood pressure until more research is conducted to confirm its effectiveness and safety."Fish oil really has effects in lowering high blood pressure," said Dr. Howard Knapp, an assistant professor of medicine at Vanderbilt University in Nashville, Tenn. "But we are not recommending fish oil as a treatment of hypertension."

Knapp published a study in The New England Journal of Medicine in which he found that among 32 men with mild high blood pressure, those who took daily high doses of fish oil for a month had lower blood pressure.

Dr. John LaRosa of the American Heart Association said the results were interesting but the study was too small to be conclusive.

"It's a preliminary sort of study which wouldn't lead anyone to make any kind of across-the-board recommendations," LaRosa said.

Since scientists realized that Eskimos, who eat large amounts of fish, rarely have heart attacks, research has been accumulating that a fatty acid found in oily cold-water fish such as salmon and mackerel may have a variety of possible health benefits.

Studies have indicated these so-called n-3 or Omega-3 fatty acids may reduce the risk for heart attacks, perhaps by thinning the blood. Other studies have suggested Omega-3s may be useful for treating diseases in which the immune system attacks the body, such as rheumatoid arthritis.

Previous studies, however, produced conflicting results about whether fish oil also lowered high blood pressure. Some studies also suggested the so-called n-6 fatty acids in vegetable oil could lower blood pressure.

The new study was designed to definitively answer those questions by comparing the two types of fatty acids directly for the first time and carefully monitor subjects' blood pressure, Knapp said.

Knapp and his colleagues gave 32 men with mild high blood pressure either low doses of fish oil, high doses of fish oil, high doses of a vegetable oil or a mixture of oils found in the typical American diet.