Fish may help prevent heart failure as well as heart attacks

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 (PDF) in the June 21, 2005, issue of the Journal of the American College of Cardiology.

“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 Women’s 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.

“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, 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.