Who should take fish oil supplements?

Based on observational studies, guidelines recommend eating fish (fresh or canned) 2 or 3 times a week as part of an overall healthy eating plan for primary and secondary prevention of cardiovascular disease.[2–3,8–11]

Fish oil supplements are a source of omega-3 long-chain fatty acids and some guidelines recommend them as an alternative to dietary sources of eicosapentanoic acid (EPA) and docosahexanoic acid (DHA).[1] For example, the Heart Foundation suggests that people with cardiovascular disease consume a total of 1000 mg daily of EPA/DHA by eating 2 to 3 serves of fish a week or by using fish oil supplements.[1]

However, the extent of any benefit in reducing cardiovascular disease is uncertain. Research has not ruled out that other factors may contribute to the cardio-protective benefit of a diet rich in fish.[5–7]

Fish oil supplements can be useful for people with hypertriglyceridaemia.[2–4] Doses of 2 to 5 g daily of total EPA/ DHA are required to lower triglyceride levels.[2]

Why is the evidence for using fish oil supplements in cardiovascular disease uncertain?

While observational research has established the link between eating fish regularly and lower rates of cardiovascular events[9–11], findings from clinical trials of fish oil supplements are inconsistent.[5,7,12]

Despite numerous trials, expert opinions are mixed about whether fish oil supplements are useful for reducing risk of cardiovascular events[1,6,7,12], and not all guidelines recommend fish oil supplementation in cardiovascular disease management.[3,4]

Although large controlled trials have reported lower rates of cardiovascular events with fish oil supplements[13,14], these findings have not been confirmed in recent trials involving people with cardiovascular disease receiving standard therapies.[5-7] Differences in study methods, populations and improvements over the last two decades in managing acute coronary events may account for the discrepancy.

Overall, evidence suggests that if there is a benefit of adding an omega-3 long-chain fatty acid supplement to current treatment of cardiovascular disease, it is probably small.[5,7] For example, one double-blinded trial involving over 3800 people with recent myocardial infarction found no difference between a total dose of 840 mg EPA/DHA and placebo on the 1-year cumulative rate of sudden cardiac death (1.5% vs 1.5%; [95% CI: -0.9% to 0.7%]).[7]

What to consider if recommending a fish oil supplement

Take into account dietary fish intake, pill burden, patient preference, and cost when deciding about a fish oil supplement. People should be advised that it is not a substitute for any of their other medicines for cardiovascular disease, such as such as aspirin, beta-blockers, statins and ACE inhibitors.

Fish oil supplements have few adverse effects and at doses ≤ 2g daily of EPA/DHA, serious adverse effects are rare.[2,15] People taking fish oil supplements at doses > 2 g daily of EPA/DHA should be informed that their blood might take longer to clot. Be vigilant for this particularly if the supplement is used in combination with antiplatelet drugs or anticoagulants.[4]

References

1. National Heart Foundation of Australia. Position statement: Fish, fish oils, n-3 polyunsaturated fatty acids and cardiovascular health, updated November 2008. (accessed 9 August 2010).
2. Rossi S, ed. Australian Medicines Handbook. Adelaide, 2011.
3. Cardiovascular Writing Group. Fish oil (omega-3 long chain polyunsaturated fatty acids), revised October 2010, etg33 March 2011:Therapeutic Guidelines Ltd. (accessed 22 July 2011).
4. Cardiovascular Writing Group. Therapeutic Guidelines: Cardiovascular. Version 5 ed. Melbourne: Therapeutic Guidelines Ltd, 2008.
5. Kromhout D, Giltay EJ, Geleijnse JM. n-3 Fatty Acids and Cardiovascular Events after Myocardial Infarction. N Engl J Med 2010;363:2015–26.
6. Galan P, Kesse-Guyot E, Czernichow S, et al. Effects of B vitamins and omega 3 fatty acids on cardiovascular diseases: a randomised placebo controlled trial. BMJ 2010;341:c6273.
7. Rauch B, Schiele R, Schneider S, et al. OMEGA, a randomized, placebo-controlled trial to test the effect of highly purified omega-3 fatty acids on top of modern guideline-adjusted therapy after myocardial infarction. Circulation 2010;122:2152–9.
8. Tonkin A, Barter P, Best J, et al. National Heart Foundation of Australia and the Cardiac Society of Australia and New Zealand. Position statement on lipid management 2005. Heart Lung Circ 2005;14:275–91.
9. He K, Song Y, Daviglus ML, et al. Fish consumption and incidence of stroke: a meta-analysis of cohort studies. Stroke 2004;35:1538–42.
10. He K, Song Y, Daviglus ML, et al. Accumulated evidence on fish consumption and coronary heart disease mortality: a meta-analysis of cohort studies. Circulation 2004;109:2705–11.
11. Whelton SP, He J, Whelton PK, et al. Meta-analysis of observational studies on fish intake and coronary heart disease. Am J Cardiol 2004;93:1119-23.
12. Hooper L, Thompson RL, Harrison RA, et al. Omega 3 fatty acids for prevention and treatment of cardiovascular disease. Cochrane Database Syst Rev 2004;CD003177.
13. Yokoyama M, Origasa H, Matsuzaki M, et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet 2007;369:1090–8.
14. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto miocardico. Lancet 1999;354:447–55.
15. Turner M.B. Safety of fish oil and omega-4 fatty acids. Medicines Safety Update No.2; 2010. Therapeutic Goods Administration (accessed 24 June 2011).