Fish Oil Cuts Risk of Sudden Death

People who eat several servings of fish each week may lower their risk of heart disease and death, two national studies report.

In one study, men without heart disease were 81% less likely to experience sudden death when their blood levels of omega-3 fatty acids were high regardless of their age, smoking habits, or the amount of other types of fatty acids in their blood.

Omega-3 fatty acids, which are found in fatty fish such as salmon and mackerel, may lower the risk of developing an irregular heart rhythm and reduce blood cholesterol and clotting — all risk factors for heart disease.

The findings point to a way for individuals to lower their risk of sudden death from heart attack.

The results suggest that increasing intake of omega-3 fatty acids by either supplements or by diet may substantially reduce the risk of sudden death, even among those without a history of heart disease.

More than 50% of people who die suddenly of cardiac causes have no signs or symptoms of heart disease.

In the first study, published in the New England Journal of Medicine researchers looked at the experience of about 22,000 male doctors who enrolled in the Physicians’ Health Study in 1982. They were all free of heart disease at the time, and about 15,000 volunteered a blood sample.

Over the next 17 years, 94 of the men who had given blood samples and who had not subsequently been diagnosed with heart disease died suddenly. The researchers chose about 180 surviving members of the study and compared them with those victims. In particular, they compared the bloodstream concentrations of substances called omega or n-3 fatty acids, found primarily in fish oils.

On average, the men who died suddenly had lower amounts of n-3 fatty acids than the ones who did not. When the researchers divided all the men into four groups based on the concentration of n-3 fatty acids in their blood, the men in the highest quarter had only a fifth the risk of sudden death as those in the lowest quarter.

In the second study, which appears in JAMA, researchers studied the experience of 85,000 female nurses. Like the physicians, they volunteered to be questioned and followed over many years as part of the Nurses’ Health Study, which began in 1976.

The researchers used dietary information gathered in five interviews between 1980 and 1994 to estimate fish intake. They also calculated the approximate amount of n-3 fatty acids consumed, based on the type of fish the women listed in their diet questionnaires.

The researchers found that the more frequently a woman ate fish, the less likely she was to suffer a heart attack or to die of any cardiac cause. Specifically, those who ate fish once a week had a 30 percent lower risk of heart attack or death as those who never ate fish. Eating fish five times a week was only slightly more beneficial; those women had a 34 percent lower risk.

Although ocean-living, cold-water oily fish such as salmon, swordfish and tuna offer the largest, easily accessible sources of n-3 fatty acids, there are others. Flax seed oil, canola oil and English walnuts all contain significant amounts of the oils.

A European study published in 1999 showed that fish oil supplements reduced the risk of sudden death in people who had previously survived a heart attack. The n-3 fatty acids appear to have a specific antiarrhythmic effect, possibly by stabilizing the membranes of heart muscle cells.

The oils also have a blood-thinning effect, like aspirin. In some observational studies, fish consumption has been associated with a lower risk of stroke. There have been anecdotal observations that fish oil supplements may have antidepressant effects as well.

The findings support a growing body of research indicating that omega-3 fatty acids may reduce the risk of heart disease and death.

The New England Journal of Medicine April 11, 2002;346:1113-1118

JAMA April 10, 2002;287:1815-1821