Fish Oils for Treating Cardiovascular Diseases – Where Is the Evidence?

By: Dr Deepak S Hiwale

All of us have heard the wondrous things that fish oils can do for optimizing your health. Found in large quantities in fish – as the name suggests – fish oils are increasingly being recommended and used for prevention (as well as management) of cardiovascular disease.

But, how do you know for sure if fish oils are indeed beneficial? Where is the evidence to prove that much of the alleged effectiveness is indeed true and not hype?

If you are one of the sceptics and doubt if fish oils are really that important, this article is just for you. Let us try to unearth some of the scientific evidence in support of the effectiveness of fish oils in cardiovascular and other diseases.

What Are Fish Oils?

Fish oils are omega-3 fatty acids; these are derived mainly from marine sources and to some extent from plant sources. Chemically, omega-3s are polyunsaturated fatty acids with double bonds starting from carbon atom positioned at 3 (when counted from the methyl end of the fatty acid).

Anti-inflammatory, antiarrhythmic and antithrombotic actions afford fish oils a number of health benefits in preventing as well as treating diseases – mainly cardiovascular. In contrast, the omega-6 fatty acids which are found in seeds, vegetables oils and meat support thrombosis and inflammation.

Sources of Fish Oils

Eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and α-linoleic acid (ALA) are the most important of fatty acids as far as humans are concerned. However, it has to be noted that human beings cannot synthesize either omega-3s or omega-6s on their own. Thus, acquiring these from dietary sources or supplementation becomes important; these are therefore called essential fatty acids (essential for their presence in diet).

As mentioned earlier, marine sources are very rich in omega-3 fatty acids – oily fish like Salmon and Tuna. To get the daily requirement of 1g of EPA and DHA, ingestion of 1.5 to 4.5oz of salmon or 4oz of canned tuna is necessary (Covington, 2004).

Vegetarian sources of omega-3s are walnuts, flaxseed oil and canola oil.

Effectiveness of Fish Oils in Cardiovascular Disease

Numerous scientific studies have reported that regular dietary intake of omega-3 fatty acids (either in the form of fish servings or as supplements) does prevent cardiovascular diseases. Some of these are:

• DART was a significant study to prove that consumption of fish caused a 29% reduction in all-cause mortality due to myocardial infarction (Burr et al., 1989)

• Sudden death due to ventricular arrhythmia is one of the main causes of deaths related to cardiovascular disease (Leaf, Kang, Xiao, & Billman, 2003). The GISSI – Prevenzione Trial reported that ingestion of omega-3 fatty acids caused a 45% reduction in the incidence of sudden death and 20% reduction in all cause mortality in such cases (1999)

• A closer look at randomized trials between 1966 to 1999 also supports the findings that omega-3s are indeed beneficial in cardiovascular disease (Bucher, Hengstler, Schindler, & Meier, 2002)

• Inhibition of synthesis of very low-density lipoprotein (VLDL), cholesterol and triglycerides in the liver seem to the mechanisms responsible for the beneficial effects of fish oils in hyperlipidemia. 4g of omega-3s daily can cause as much as 30% reduction in serum triglyceride concentration (Harris et al., 1997; Harris, 1997)

• Fish oils have also been shown to reduce blood pressure in those suffering from hypertension (Howe, 1997; Morris, Sacks, & Rosner, 1993)

• Fish oils combined with fenofibrate has been shown to be quite effective in reducing triglyceride levels in blood (Gerber et al., 2008)

Effectiveness of Fish Oils in Other Diseases

In addition to cardiovascular diseases, fish oils have proved their effectiveness in rheumatoid arthritis as well.

• Omega-3s taken in excess of 3g a day reduce the severity of symptoms – morning stiffness and swelling of joints (Kremer et al., 1990; Volker, Fitzgerald, Major, & Garg, 2000)

• Some studies have suggested that reducing consumption of omega-6s while supplementing with omega-3s can help reduce the symptoms of rheumatoid arthritis to the extent that there is no further need to take non-steroidal anti-inflammatory drugs (James & Cleland, 1997; Vargova, Vesely, Sasinka, & Torok, 1998)

Recommended Use of Fish Oils

The American Heart Association (Kris-Etherton, Harris, & Appel, 2002) has laid down dosage recommendations for intake of fish oils in cardiovascular disease. These are:

• for prevention of development of cardiovascular disease – 2 servings of fish per week along with other foods rich in ALA (walnuts, canola and flaxseed oils)

• to arrest the worsening of existing heart disease – oily fish that will deliver 1g of EPA plus DHA on a daily basis; supplements providing the necessary dose can also be used

• to lower triglyceride levels in blood – 2-4g of DHA plus EPA

Fish Oil Supplements

A commercially available capsule (1000mg) of fish oil typically contains 180mg of EPA and 120mg of DHA. Thus, to attain the daily recommended dose of 0.9g, three capsules will need to be taken (Kris-Etherton et al., 2002) – these should be usually spaced out evenly during the day. Liquid formulations of fish oils are also available; these usually contain 1-3g of omega-3 fatty acids.

Conclusion

Regular servings of fish (preferably oily) and foods rich in omega-3 fatty acids, in addition to supplementing with omega-3 capsules, seems like a good strategy for preventing or arresting the further development of cardiovascular disease.

References

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 (1999). Lancet, 354, 447-455.

Bucher, H. C., Hengstler, P., Schindler, C., & Meier, G. (2002). N-3 polyunsaturated fatty acids in coronary heart disease: a meta-analysis of randomized controlled trials. Am J Med, 112, 298-304.

Burr, M. L., Fehily, A. M., Gilbert, J. F., Rogers, S., Holliday, R. M., Sweetnam, P. M. et al. (1989). Effects of changes in fat, fish, and fibre intakes on death and myocardial reinfarction: diet and reinfarction trial (DART). Lancet, 2, 757-761.

Covington, M. B. (2004). Omega-3 fatty acids. Am Fam.Physician, 70, 133-140.

Gerber, J. G., Kitch, D. W., Fichtenbaum, C. J., Zackin, R. A., Charles, S., Hogg, E. et al. (2008). Fish oil and fenofibrate for the treatment of hypertriglyceridemia in HIV-infected subjects on antiretroviral therapy: results of ACTG A5186. J Acquir.Immune.Defic.Syndr., 47, 459-466.

Harris, W. S. (1997). n-3 fatty acids and serum lipoproteins: human studies. Am J Clin Nutr., 65, 1645S-1654S.

Harris, W. S., Ginsberg, H. N., Arunakul, N., Shachter, N. S., Windsor, S. L., Adams, M. et al. (1997). Safety and efficacy of Omacor in severe hypertriglyceridemia. J Cardiovasc.Risk, 4, 385-391.

Howe, P. R. (1997). Dietary fats and hypertension. Focus on fish oil. Ann N Y.Acad.Sci., 827, 339-352.

James, M. J. & Cleland, L. G. (1997). Dietary n-3 fatty acids and therapy for rheumatoid arthritis. Semin.Arthritis Rheum., 27, 85-97.

Kremer, J. M., Lawrence, D. A., Jubiz, W., DiGiacomo, R., Rynes, R., Bartholomew, L. E. et al. (1990). Dietary fish oil and olive oil supplementation in patients with rheumatoid arthritis. Clinical and immunologic effects. Arthritis Rheum., 33, 810-820.

Kris-Etherton, P. M., Harris, W. S., & Appel, L. J. (2002). Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation, 106, 2747-2757.

Leaf, A., Kang, J. X., Xiao, Y. F., & Billman, G. E. (2003). Clinical prevention of sudden cardiac death by n-3 polyunsaturated fatty acids and mechanism of prevention of arrhythmias by n-3 fish oils. Circulation, 107, 2646-2652.

Morris, M. C., Sacks, F., & Rosner, B. (1993). Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation, 88, 523-533.

Vargova, V., Vesely, R., Sasinka, M., & Torok, C. (1998). [Will administration of omega-3 unsaturated fatty acids reduce the use of nonsteroidal antirheumatic agents in children with chronic juvenile arthritis?]. Cas.Lek.Cesk., 137, 651-653.

Volker, D., Fitzgerald, P., Major, G., & Garg, M. (2000). Efficacy of fish oil concentrate in the treatment of rheumatoid arthritis. J Rheumatol., 27, 2343-2346.

Source: healthguidance.org