No benefit of low doses omega-3 fatty acids in patients with previous heart attack

22/02/2011

Low doses of omega-3 fatty acids did not reduce the overall rate of major cardiovascular events in patients who have had a previous myocardial infarction (MI) in the Alpha Omega Trial.

N-3 (or omega-3) fatty acids can be divided in two main classes: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived from fish; and alpha-linolenic acid (ALA) from plant foods such as soybean oil and walnuts. He noted that several intervention studies in cardiac patients have shown that a daily intake of 1-2 g of EPA + DHA via fish oil capsules has been associated with a reduced mortality from coronary heart disease, and epidemiological studies in healthy populations have also suggested that 250 mg EPA + DHA or eating fish once or twice a week can lower the risk of cardiovascular disease. For ALA, there is less evidence of a cardioprotective effect.

The Alpha Omega Trial was designed as a dietary intervention study to examine the effect of low doses of omega-3 fatty acids on major cardiovascular events. In the study, 4,837 men and women who had suffered a heart attack approximately four years previously were randomised to daily use of one of four margarines for 40 months: containing EPA + DHA (400 mg/day); ALA (2 g/day); both EPA + DHA and ALA; or placebo.

Results showed no reduction in major cardiovascular events in any of the omega-3 groups compared to placebo. However, among sub-groups, there was a borderline significant reduction in major cardiovascular events in women who received ALA. In addition, in patients with diabetes, omega-3 fatty acids were protective against ventricular arrhythmia-related events, and the EPA + DHA combination appeared to be associated with a reduction in CHD mortality.

Professor Kromhout suggested that the lack of any effect in the overall population may have been due to the amount of other treatments being taken by the patients, with 98% on antithrombotic agents, 90% on antihypertensive drugs, and 86% on lipid lowering drugs. "We found that cardiovascular mortality rate in the study population was only half that expected, probably because of their excellent treatment. This may also be why the rate of major cardiovascular events during follow-up was no lower in the fatty acid groups than in the placebo group," he speculated.

After a heart attack, conventional prescription medicines do seem effective at preventing further attacks. However, high doses of omega-3 fatty acids may still have a role in cardiovascular health and have been shown to be beneficial in preventing cardiovascular disease (see below).

How fish is cooked affects cardiovascular benefits

It is well known that omega-3 fatty acids found in fish have some cardiovascular benefits, but new research shows that how the fish is cooked is also important. A study by researchers from the University of Hawaii at Manoa, Honolulu, Hawaii, US, showed that baked or boiled fish is associated with more benefit from omega-3 fatty acids than fried, salted or dried fish. It also found that eating fish with low-sodium soy sauce or tofu will enhance the benefits.

In addition, the findings suggest that the cardioprotective benefits vary by gender and ethnicity, due perhaps to the preparation methods, genetic susceptibility or hormonal factors. Specifically, it showed that Caucasian, Japanese-American and Latino men may be more likely to get the health benefits of fish than African-American or Hawaiian men, and that omega-3s from plant sources, such as soy, may do more to improve women's heart health than fish sources. "It appears that boiling or baking fish with low-sodium soy sauce (shoyu) and tofu is beneficial, while eating fried, salted or dried fish is not," said lead researcher, Ms Lixin Meng.

In the study, researchers examined the source, type, amount and frequency of dietary omega-3 ingestion among 82,243 men and 103,884 women of African-American, Caucasian, Japanese, Native Hawaiian and Latino descent ages 45 to 75 years old with no history of heart disease. They found that those in the highest quintile of omega-3 intake consumed a median 3.3 g a day, while those in the lowest quintile consumed a median of 0.8 g a day. During the average 11.9 years of follow-up, 4,516 heart-related deaths occurred in the group, according to state and national death records, which were cross-referenced through the end of 2005.

Results showed that omega-3 intake was inversely associated with overall risk of death due to heart disease in men – a trend mainly observed in Caucasians, Japanese Americans and Latinos. However, there weren't many blacks or Hawaiians in the study, so the results should be interpreted cautiously, Ms Meng said.

Eating tofu also had a cardioprotective effect in all ethnic groups.

Overall, men who ate about 3.3 g per day of omega-3 fatty acids had a 23% lower risk of cardiac death compared to those who ate 0.8 g daily. Furthermore, adding less than 1.1 g/day shoyu and teriyaki sauce at the dinner table was protective for men.

For women, the omega-3 effect was mildly cardioprotective at each level of consumption. Salted and dried fish was a risk factor for heart disease in women; baked or boiled fish was associated with more benefit, and more shoyu use was associated with less risk of death from heart disease in women.

Baked or boiled fish with low-sodium soy sauce or tofu will enhance the benefits!

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