EVIDENCE- BASED COMMENTARY
FISH OIL TO PREVENT HEART DISEASE: THE EVIDENCE AND THE CONTROVERSY
Ong Hean Teik FACC, FRCP(Glas, Edin)
HT Ong Heart Clinic
Address for correspondence: Dr HT Ong, H T Ong Heart Clinic, 251-C Burma Road, 10350 Penang. Tel: 04-2292875, Fax: 04-2292877, Email: email@example.comOng HT. Fish oil to prevent heart disease: the evidence and the controversy. Malaysian Family Physician. 2006;1(2&3):65-66
In November 2002, the American Heart Association, after a comprehensive review, announced that fish oil reduces heart disease and recommended that patients consume daily 1gram of marine derived omega-3 fatty acids (comprising eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA).1 Yet, the BMJ recently published a report suggesting that fish oil is of no value in heart disease.2 What are we to believe, and does omega-3 really protects against heart disease?
The idea that fish oil may be useful came about because communities that consume large quantities of fish, such as the Eskimos and Japanese, seem to have a low incidence of heart disease. Further research showed that even in the same community, those who eat more fish are better off. A 30-year follow up study of men in Chicago showed that those men who consume 35 g or more of fish daily had a 38% lower risk of heart disease mortality.3 Similarly, in 85,000 women followed for 16 years, those who take fish 2 to 4 times a week had a 31% lower risk of death from heart disease compared to those rarely eating fish.4 A 12-year study of 43,671 men showed that those eating fish 1 to 3 times a month had a 43% lower risk of strokes compared to those eating fish less than once a month.5The next step in trying to confirm the protective effect of fish oil calls for concrete evidence from randomised placebo-controlled trials. In 1999, the Italian GISSI investigators reported their trial of over 11,000 heart patients given fish oil, vitamin E, both or neither.6 After 3.5 years, the risk of death, heart attacks or stroke was reduced with fish oil by 10%, and the risk of dying of heart disease was reduced by 17%. Vitamin E was found to be of no benefit. In 1999, von Schacky reported a placebo-controlled study on 233 patients with angiographic coronary artery disease given fish oil supplements for 2 years.7 In patients on fish oil, 29% of the coronary vessel segments saw a reduction of narrowing, with 71% of segments having an increase in their obstruction severity. This compares with only 15% of the diseased segments improving in the placebo group, and 85% of segments seeing an increase in narrowing. This difference between the fish oil group and the placebo group is statistically significant (p<0.05).
Since many of the fish oil trials enrolled small number of patients, pooling these studies may provide a clearer idea of the appropriateness of treatment. In 2002, Bucher and colleagues reported their meta-analysis of 11 trials, in which 7951 patients were put on fish oil and 7588 patients were in the control group.8 The risk of fatal heart attacks was reduced by 30% (p<0.001), and overall death rates reduced by 20% (p<0.001) in the treated group. The highly significant p values strongly support the conclusion of the authors that omega-3 fatty acids are beneficial for patients with coronary disease. In April 2005, Studer and colleagues reviewed 97 studies that enrolled 276,116 patients studying whether different lipid lowering medicines or dietary changes had an effect on mortality rates.9 Only those receiving the statins and fish oil saw a significant reduction of overall mortality, with a reduction of 13% with statins and 23% with fish oil. Writing in the March 2006 issue of the American Heart Journal, Defilippis and Sperling conclude that fish-derived, and even plant-derived, omega-3 fatty acids favourably affect cardiovascular health.10
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