The consumption of oily fish as a protective factor against developing cardiovascular disease stems from observations of fish-eating communities such as Greenland Eskimos. There have been multiple studies looking at the association between fish intake and cardiovascular disease within large populations. Whilst the findings have been relatively inconsistent, a 2004 meta-analysis of 13 of the largest studies performed found that individuals who consumed fish just once a week were found to have a significantly lower risk of developing cardiovascular disease than those who never consumed fish, or ate fish less than once a month (He 2009). It has also been found that the amount of circulating omega-3 in the blood (plasma and red blood cells – which reflects the quantity of omega-3 in the heart muscle) is related to the risk of developing cardiovascular disease. The higher the amount of circulating omega-3 – the lower the risk (Harris et al, 2004).
However, the relationship between fish intake and heart failure appears to be somewhatcloudy in comparison. Heart failure differs from heart disease in that, in the former, it is the inability of the heart to pump blood efficiently to provide adequate flow to the body and organs. The condition generally occurs as the end point of several possible disease processes, including: coronary artery disease, hypertension, valve defects, and in cases of long term alcohol abuse or viral infection, all of which can lead to weakness of the heart muscle. Chronic heart failure is extremely common and one of the leading cause of death in the Western world. The condition affects an estimated 400,000 people in the UK, with approximately 8,000 at an advanced stage. The number of patients presenting with heart failure is increasing steadily, particularly in the elderly, and consequently the burden of this disease is reflected in stretched health care resources within the UK.
To date, there have only been a few studies that have looked directly at the relationship between fish intake and the risk of heart failure, and these studies have reported conflicting findings. However, this may be due to the variation of omega-3 intake reported between studies and that, in some cases, participants simply consumed too little fish to offer any real cardio-protective effects against developing heart failure.
However, whilst the association between fish intake and heart failure risk is still somewhat unclear, the evidence that omega–3 plays a positive role in treatment of the disease is certainly more solid. For example, two large studies (the GISSI-HF trial and the JELIS trial) indicate the use of omega–3 supplementation as a safe treatment option for supplying concentrated and relatively high doses of long chain fatty acids to heart failure patients (Travazzi et al, 2008; Yokoyama et al, 2007).
The use of omega-3 supplementation as a treatment for heart failure, and the need to clarify the importance of dose and concentration, has been a topic of discussion in a recent publication in the Journal of the American College of Cardiology (Tang et al, 2010) Omega-3 appears to offer a viable, well tolerated therapy for heart failure patients through their anti-arrhythmic and anti-inflammatory properties. It appears, however, that higher, or ’pulse’ doses of omega-3, may be needed to achieve more favourable outcomes, and that prescription-strength, high-dose omega-3 regimens differ significantly from the lower and inconsistent dosages found in many non –pharmaceutical-grade over-the-counter supplements. In other words, simply telling patients to take “fish oil” supplements without taking account of the importance of purity, concentration and dosage is most unlikely to yield the same benefits consistently seen in intervention trials.
Certainly, whilst there are known health benefits attributed to supplementing the diet with fish oils, it is becoming clearer that the dosage needed to exert biological changes within the body is much higher than levels typically consumed. Generic fish oil contains a mixture of different fatty acids, so the concentration of important omega-3fatty acids is relatively low. Indeed, these oils, known as triglycerides, can only achieve a maximum 30% omega-3, a stark contrast to the 70% ethyl-ester EPA content of Vegepa. Furthermore, very high concentrations of omega-3 in ethyl-ester form have higher uptake than formulations containing lower concentrations, and show significant advantages for cardiovascular health over omega-3 in triglyceride form. The choice of oil is therefore of paramount importance when considering supplements for both their preventive and therapeutic effects on heart health and is a message that needs to be reinforced when advising heart failure patients.
1. He, K. Fish, long-chain omega-3 polyunsaturated fatty acids and prevention of cardiovascular disease–eat fish or take fish oil supplement? Prog Cardiovasc Dis 52, 95-114 (2009).
2. Harris, W.S. et al. Omega-3 fatty acids in cardiac biopsies from heart transplantation patients: correlation with erythrocytes and response to supplementation. Circulation 110, 1645-1649 (2004).
3. Tavazzi, L. et al. Effect of n-3 polyunsaturated fatty acids in patients with chronic heart failure (the GISSI-HF trial): a randomised, double-blind, placebo-controlled trial. Lancet 372, 1223-1230 (2008).
4. Yokoyama, M. et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet 369, 1090-1098 (2007).
5. Tang, W.H.W. & Samara, M.A. Polyunsaturated Fatty Acids in Heart Failure Should We Give More and Give Earlier? J Am Coll Cardiol (2010).doi:10.1016/j.jacc.2010.11.014