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(BETHESDA, MD) – For older adults who haven’t added weekly servings of fish to their diets, new Harvard-led research offers more reasons to get hooked on tuna and other broiled or baked fish rich in omega-3 fatty acids.
According to the research, published in the Aug. 1, 2006, issue of the Journal of the American College of Cardiology, moderate consumption of fish rich in long-chain omega-3 fatty acids appears to have a direct effect on the electrical function of the human heart. This function affects heart rhythm, including whether a person’s heart beats too quickly or too slowly.
The study states that for people age 65 or older, eating fish just once or twice a week (in 3-ounce to 5-ounce servings) may help to:
- lower the resting heart rate,
- slow the time between when the heart is signaled to pump blood and the pumping occurs,
- reduce the risk of the heart’s electrical system not resetting properly after each beat.
All of these factors can play a role in abnormal heart rhythms and sudden cardiac death, which claims the lives of hundreds of thousands of people every year, says study leader Dariush Mozaffarian, MD, DrPH, FACC, a cardiologist and instructor of medicine at Brigham and Women’s Hospital, Harvard Medical School in Boston. And these factors, he says, appear to be positively influenced by eating fish rich in omega-3 fatty acids.
“The good news is that we’re not talking about a large amount of fish intake, or fish oil supplements, but rather modest fish intake, one to two servings per week,” Dr. Mozaffarian said. “But that modest intake may have important benefits.”
For those who want to add more fish to their diets, the type of fish and the cooking method may affect the health benefits, Dr. Mozaffarian said.
“In contrast to intake of tuna or other broiled or baked fish, intake of fried fish had no association with the heart’s electrical parameters,” he said. “Previously, we have seen that intake of fried fish – which in the U.S. are most often commercially sold fish burgers or fish sticks – is not associated with blood levels of omega-3 fatty acids. This suggests that it may be the omega-3 fatty acids in tuna and other broiled or baked fish that are having a positive impact on the heart’s electrical parameters.”
Omega-3 fatty acids are considered essential for good health, but long-chain omega-3 polyunsaturated fats are not produced naturally by the body. Instead, they must be consumed in seafood, such as albacore tuna and other cold-water fish, including salmon, mackerel and lake trout.
For their study, Dr. Mozaffarian and his colleagues analyzed data collected from 5,096 men and women participating in the Cardiovascular Health Study, begun in 1989 and sponsored by the National Heart, Lung and Blood Institute. The researchers used dietary questionnaire information to determine whether the people were eating fish less than once per month, one to three times per month, one to two times per week, three to four times per week or more than five times per week. The researchers then compared the average year’s worth of fish consumption habits with electrocardiogram (ECG) test results.
Overall, the researchers found that eating tuna or other baked or broiled fish was associated with a lower heart rate (p trend <0.001); a slower time between when the heart received a signal to pump blood and its main pumping chamber responded (p trend = 0.03); and a lower likelihood of a prolonged resetting period for the heart’s electrical system (p trend = 0.03.)
Although the researchers noted increasing benefit with higher levels of fish consumption, most of the benefit was achieved by eating fish once or twice per week, particularly for heart rate, Dr. Mozaffarian said.
Future studies will seek to clarify the effects of omega-3 fatty acids and what those effects mean for treating patients with heart disease and for preventing heart disease in others.
“One interesting question is whether the effect on heart rate is a marker for clinical benefit,” Dr. Mozaffarian said. “I think that’s one important next step. Another important next step is to determine what mechanisms are producing the effects on the heart’s electrical activity. For example, is it an effect on adrenalin production by the body, or a direct effect on the heart cells? Understanding these issues may clarify greatly the mechanisms for effects of fish intake on sudden cardiac death.”
In addition to Dr. Mozaffarian, researchers from Wake Forest University School of Medicine in Winston-Salem, N.C.; Washington University School of Medicine in St. Louis; and the University of Washington in Seattle, contributed this study.
Cardiologist Humberto Vidaillet, M.D., FACC, and epidemiologist Robert Greenlee, PhD, MPH, both of Marshfield Clinic Research Foundation in Wisconsin, were not connected with the research, but said it provides further evidence that the beneficial relationships between eating fatty fish and reducing the risk of heart arrhythmias and sudden cardiac death may be real.
“Based on previously existing research on this topic, the American Heart Association already recommends eating fish twice a week as part of a diet that includes a variety of nutritious foods from all the food groups, Dr. Vidaillet said. “Oily fish rich in omega-3 polyunsaturated fatty acids, such as salmon, trout, herring, etc. are particularly recommended, as are fish prepared by grilling, baking or poaching, as opposed to frying with added saturated or trans fats. This new data provides further support for patients with a goal of reducing risk of death from coronary artery disease to follow such recommendations.”
Dr. Greenlee notes the new study doesn’t examine specific disease or mortality outcomes, but rather intervening heart measures thought to be favorable. Still, he said, the results are important.
“While it is always possible that unmeasured factors which correlate with fish intake are responsible for the favorable heart characteristics, these new findings are consistent with the results of other research and will help guide future studies,” Dr. Greenlee said.
Also in this issue of JACC
A second Harvard-led study in the Aug. 1 issue of the Journal of the American College of Cardiology re-examines data collected during four large trials comparing the potential benefits of high-dose vs. standard-dose statin therapy.
According to the research, intensive lipid lowering with high-dose statin therapy provides a significant benefit over standard-dose therapy in preventing predominantly non-fatal cardiovascular problems, including unstable chest pains, heart attacks and strokes.
In the authors’ words: “Extrapolating these data indicates that for every million patients with chronic or acute coronary artery disease, such as those entered into these trials, treated for 5 years, intensive rather than standard statin dosing would prevent more than 35,000 cardiovascular events [including more than 14,000 coronary deaths or MIs (heart attacks).]”
Sources quoted in this news release do not report any potential conflicts of interest regarding this topic.
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The American College of Cardiology is leading the way to optimal cardiovascular care and disease prevention. The College is a 34,000-member nonprofit medical society and bestows the credential Fellow of the American College of Cardiology upon physicians who meet its stringent qualifications. The College is a leader in the formulation of health policy, standards and guidelines, and is a staunch supporter of cardiovascular research. The ACC provides professional education and operates national registries for the measurement and improvement of quality care.
The American College of Cardiology (ACC) provides these news reports of clinical studies published in the Journal of the American College of Cardiology as a service to physicians, the media, the public and other interested parties. However, statements or opinions expressed in these reports reflect the view of the author(s) and do not represent official policy of the ACC unless stated so.