up a defence against heart attacks, medical researchers reported this week.

A University of Washington, Seattle, study added to the growing amount of evidence that eating fish is good for the cardiovascular system -- though no one is sure why.

Researchers studied the diets of 334 victims of sudden heart attacks and 493 people in a control group who had similar characteristics but were otherwise healthy.

They correlated heart attack risk with fish consumption and the presence in the body of a particular type of fatty acid found in most fish and shellfish.

The study found moderate amounts of the fatty acid, called long-chain n-3, could reduce the risk of sudden heart attack sharply -- from roughly two people in 10,000 to fewer than one in 10,000.

Heart disease is fatal to nearly one million Americans each year, ranking it as the nation's top killer.

More than one-quarter of those deaths occur without warning with the first heart attack, according to the American Heart Association.

In the current study, published in the Journal of the American Medical Association, researchers asked questions about subjects' diets and also took blood samples to determine the levels of n-3 in blood cells.

They determined that moderate levels of n-3 -- corresponding to one serving of a so-called fatty-fish such as salmon each week -- was the best protection against sudden heart attack.

"These particularly polyunsaturated fats get incorporated into cell membranes...and may aid in heart cell function,'' study author David Siscovick said in a telephone interview.

The fatty acid from fish may provide heart cell membranes with the strength or flexibility to expand and contract rapidly as the heart beats, he said.

Problems with heart cells could lead the heart to fibrillate or spasm.

The n-3 substance may also reduce the clumping of blood platelets and play a role in preventing blockage of the arteries, or arteriosclerosis, that can trigger heart attacks, the study said.

Numerous previous studies have shown that residents of communities where fish is a regular part of the diet suffer fewer heart problems, although there has been no conclusive finding on why eating fish is beneficial.

Other studies that examined consumption of fish oil did not find a similar benefit, perhaps because the much-higher dosages of fish oil taken in pill form did not act on the body in the same way.

*** A poultry scientist at the University of Nebraska is studying eggs that might help lower the risk of heart disease by increasing the amount of "good'' cholesterol in a person's blood.

Called Omega eggs, they are said to have high levels of omega-3 fatty acids, which increase the ratio of good to `bad' cholesterol.

Poultry nutritionist Sheila Scheideler says these eggs could help lower the risk of cardiovascular disease. The fatty acids are required for certain body and brain functions, but are not manufactured in the human body.

University nutrition scientist Nancy Lewis is completing a study to determine how Omega eggs and regular eggs affect people with high cholesterol levels.

Omega-3 fatty acids also are important in neural development in premature babies and infants, Mrs. Scheideler said.

The eggs are created by feeding hens a diet of 15 percent flax seed. A total of 140 hens at the university's poultry research facility are being fed the diet, which "provides a potent source of the omega-3 fatty acid,'' Mrs.

Scheideler said. "The chicken is remarkable.

She'll take the fatty acid and deposit it directly into the yolk, unaltered.'' Student athletes at the school's training table are served 50 dozen to 60 dozen of the Omega eggs each month.

Results of Ms Lewis' study on cholesterol effects will not be released until spring, but participants liked Omega eggs so much they wanted to know where they could buy them.

Omega eggs are available for 80 cents per dozen at a dairy store on the Nebraska campus, 20 cents more than the store's regular eggs. Omega eggs cost more because flax seed is more expensive to feed than soybeans.

Flax is a crop grown in northern Minnesota, North Dakota and Canada.

The fibre from the flax stalk is used to make linen.

Omega eggs are new to the Midwest, but they were available earlier in Washington state, Oregon and Canada.

The market is strong in those areas, and developed following research in Canada.

In addition to Omega eggs, the omega-3 fatty acids are also available to people when they eat flax seed or in deep sea fish such as salmon.