Two new studies show that people who eat substantial amounts of oily
fish are greatly protected from sudden, unexpected death, a common
condition usually caused by severely abnormal heart rhythms.
The studies -- which drew their conclusions from long-term observation
of tens of thousands of people -- greatly bolster the evidence that eating
fish regularly can have major health benefits. While most of the earlier
studies involved only men, one of the new studies demonstrates how fish
benefit women.
The benefits for men and women appear to come mostly from fish's effect
on the risk of sudden cardiac death. In the study involving women, fish
protected against nonfatal heart attacks, too.
Each year, about 220,000 Americans experience sudden death, collapsing
and dying within an hour, often before they get to a hospital. In most
cases, an abnormal heart rhythm arising from heart disease is believed to
be the cause. In about 50 percent of the cases, however, the victim is
unaware of that heart disease. There is no chest pain or previous heart
attack. Instead, sudden death is the first symptom of the problem.
"Prevention is really the only way to impact the rate and mortality
from sudden death," said Christine A. Albert, a cardiologist at Brigham
and Women's Hospital in Boston who headed one of the studies. "One way you
could do it in a population that's healthy is through diet and
lifestyle."
In the first study, published in this week's New England Journal of
Medicine, Albert and her colleagues 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 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 today's Journal of the American
Medical Association, a team led by JoAnn E. Manson, also a physician at
Brigham and Women's Hospital in Boston, 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.
The scientists involved in the studies said that while eating fish is a
good thing to do, people should not jump to the conclusion that fish oil
supplements are an equivalent or a substitute.
"I don't think they're quite ready for prime time," said Manson. "In
terms of public health recommendations, it would be best to try to get the
. . . fatty acids through the diet. It's a relatively simple and low-cost
means of reducing risk from heart disease."
Terry A. Jacobson, a physician at Emory University who has studied the
effects of fish oils on heart disease, said he believes the new studies
"have large public health implications." He added, however, that before
fish oils can be used as preventive medicine in healthy people, a study
needs to be done in which people are randomly assigned to either get the
oils or a placebo.
He said he plans to propose such a study to the National Institutes of
Health in the near future. He said at least 6,000 people would need to be
enrolled and observed for at least three or four years.
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.
