Fish oil and severe heart rhythms - does it really help?
(December 2005)

Oily fish contain omega-3 polyunsaturated fatty acids. It is thought those fatty acids get into heart muscle and act as stabilizers, preventing severe, potentially lethal, abnormal rhythms that may occur during heart attacks or even in the absence of heart attacks. These abnormal rhythms are responsible for most sudden cardiac (heart) deaths.

In a well-designed study of "fish oil", 200 patients who had suffered severe arrhythmias called ventricular tachycardia or ventricular fibrillation and had devices called defibrillators implanted in the heart were given either 1.8 grams (a good dose) of a synthetic fish oil or served as controls. They were then followed for up to two years for development of the severe heart rhythms. The results were surprising. Those given fish oil actually had more episodes of severe abnormal rhythms than the controls, leading the authors to conclude that giving supplemental fish oil to certain patients with a history of having experienced certain types of severe heart rhythms may actually result in increased risk of experiencing new episodes of those abnormal rhythms.

Commentary: This is a solid study. The authors cite one other study in which administration of fish oil or increasing fish in the diet was associated with an increased risk of sudden cardiac death. However, the bulk of the evidence indicates that a good intake of oily fish (or probably fish oil supplements or plant sources of omega-3 fatty acid) will not prevent heart attacks, but will reduce the risk of sudden death after a heart attack.

This study looked at occurrence of abnormal rhythms, not sudden deaths. That is a relatively minor issue. A bigger issue is that this study used a fish oil provided by a pharmaceutical company that is, at least in part, synthetic. The effects of the fish oil used could be very different from eating oily fish or even using natural fish oils, and that could potentially explain the increased risk of abnormal rhythms. It is also not clear whether these results would apply to people who do not have the defibrillating device in their hearts. In other words, this is a very special group and the results may not be applicable to the general population at risk of heart attacks.

This study should not change the recommendation for eating oily fish once or twice a week ( CLICK HERE for a table of fish with good omega-3 fatty acid content). Those who do not like fish can get their omega-3 from plant or plant oil sources ( CLICK HERE for good plant sources). Omega-3 fatty acids may have additional benefits such as prevention of mental decline or Alzheimer's (not proved) - see Editor's View on omega'3 fatty acids under "Omega 3" in the Archives.

Raitt, M.H., et al. Fish oil supplementation and risk of ventricular tachycardia and ventricular fibrillation in patients with implantable defibrillators. Journal of the American Medical Association. Vol 293 (June 15) Pgs 2884-2891. 2005.

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