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Eating Fish Helps Older People Avoid Heart Failure
Prior research shows it also lowers heart attack risk
June 21, 2005 - Older people who ate fish once or
twice a week had a 20 percent lower risk of developing congestive heart
failure during 12 years of follow-up, according to a new study, which
emphasizes this does not include fried fish.
Intake of tuna fish or other broiled or baked
fish, but not fried fish, was associated with lower risk of developing
heart failure. Lower risk was seen with intake just once or twice per
week, said Dariush Mozaffarian, M.D., M.P.H., F.A.C.C., at the Brigham
and Womens Hospital, Harvard Medical School and Harvard School of
Public Health in Boston, Massachusetts.
This is the first study to look at fish intake and
the development of heart failure and it appears in the todays issue of
the Journal of the American College of Cardiology.
Prior studies have shown fish intake to be
associated with lower risk of fatal heart attacks. The results of the
present study suggest that intake of fatty fish high in omega-3 fatty
acids may reduce the risk of developing heart failure as well, Dr.
Mozaffarian added.
From 1989 to 1990, the researchers gave diet
questionnaires to 4,738 adults in four cities who were 65 or older and
free of congestive heart failure. During 12 years of follow-up, 955
participants developed congestive heart failure. After adjusting the
results for other risk factors, those who had reported that they ate
tuna or other fish once or twice a week were 20 percent less likely to
develop congestive heart failure than those who said they ate such fish
less than once a month. Eating fish three or four times a week was
linked to a 31 percent lower risk of developing congestive heart failure
over the next 12 years. However, fried fish consumption was linked to a
higher risk of congestive heart failure.
This study, as well as the results of our prior
work, suggests that the type of fish meal consumed is likely to affect
the degree of cardiovascular benefit one might receive. This study
suggests that intake of fried fish, particularly lean (nonfatty or
white) fish, is unlikely to provide the same cardiovascular benefits as
fatty or oily fish, Dr. Mozaffarian said.
The benefits appeared to be connected with the
amount of omega-3 fatty acids the participants consumed. Those with the
highest levels of long-chain n-3 fatty acid intake had a 37 percent
lower risk of congestive failure than those with the lowest intake.
Intake of tuna and other broiled or baked fish was
associated with higher blood levels of omega-3 fatty acids in this
study, suggesting these were mostly fatty, oily fish higher in omega-3
fatty acid content. Omega-3 fatty acids have a variety of effects that
might reduce risk of developing heart failure, including beneficial
effects on blood pressure, arterial resistance, endothelial cell
function, inflammation, and heart rate, Dr. Mozaffarian said.
Dr. Mozaffarian noted that intake of fried fish was
not associated with blood levels of omega-3 fatty acids in this study.
Because frying does not destroy omega-3 fatty acids in fish, this
suggested that most fried fish consumed by these older adults were lean,
white fish species, which tend to have low levels of omega-3 fatty
acids. Also, he pointed out that frying may add harmful substances, such
as trans-fats and oxidation products. The absence of observed benefit
with fried fish intake might therefore be related to the combination of
low levels of omega-3 fatty acids and potential harmful effects of the
cooking process, he said.
Other studies have highlighted the potential
benefits of salmon, but Dr. Mozaffarian said that other than tuna, this
study did not collect detailed data about specific species of fish.
However, based on other information about types of
fish commonly consumed in the U.S., he believes that a significant
proportion of the fish in the other broiled or baked fish category was
likely salmon.
Dr. Mozaffarian did note that the U.S.
Environmental Protection Agency has published recommendations regarding
safe levels of fish intake for women who may become pregnant and nursing
mothers, in part because of concerns about mercury.
For the general population, effects of long-term
mercury exposure on cardiovascular health are not well-established,
while considerable evidence exists for benefits of fatty fish
consumption. So, on average, low levels of mercury are unlikely to
counteract the benefits of the omega-3 fatty acids in fatty fish.
Rather, the main question is whether the benefits of eating fatty fish
would be even greater if mercury were not present, he said.
Dr. Mozaffarian pointed out that this was an
observational study, and that while a variety of other risk factors,
lifestyle habits and dietary characteristics were taken into account, it
is possible that other unmeasured lifestyle or dietary differences
explain part of the observed relationships. He said further studies are
needed to confirm the results.
Paul G. Shekelle, M.D., Ph.D., at RAND in Santa
Monica, Calif., who was not connected with this study, said it is an
advance, but should be kept in perspective.
As an observational study assessing the
association between fish intake and incidence of congestive heart
failure, this is definitely stronger in design and execution than much
of the omega-3 fatty acids literature. However, there is still a pretty
big gap between convincingly demonstrating an association and concluding
that increasing one's fish intake or, more likely, taking supplemental
omega-3 will help prevent congestive heart failure. One only has to
remember the hormone replacement therapy story to recognize the pitfalls
of generalizing from good observational evidence to an intervention,
Dr. Shekelle said.
The data was collected as part of the
Cardiovascular Health Study, which is a multicenter study sponsored by
the National Heart Lung and Blood Institute to evaluate risk factors for
cardiovascular disease in older adults. The research team also included
investigators at the Veterans Affairs Puget Sound Health Care System and
the University of Washington in Seattle and Wake Forest University
School of Medicine in Winston-Salem, N. C.. The participants were
recruited from the areas around Sacramento, Calif.; Hagerstown, Md.;
Winston-Salem, N. C. and Pittsburgh, Pa.
The American College of Cardiology, a 31,000-member
nonprofit professional medical society and teaching institution, says it
is dedicated to fostering optimal cardiovascular care and disease
prevention through professional education, promotion of research,
leadership in the development of standards and guidelines, and the
formulation of health care policy.
For the complete study click here.
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