Fish oils reduce cardiac deaths
Fish oil supplements significantly reduce cardiac mortality, a systematic review has confirmed, but the mechanism is still unknown.
The review assessed the effects of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on mortality and cardiac arrhythmias. Randomised controlled trials of fish oil, as dietary supplements, were included. The primary outcome was an arrhythmic endpoint of appropriate implantable cardiac defibrillator (ICD) therapy and sudden cardiac death. The secondary outcome was all cause mortality and death from cardiac causes.
There were 12 studies with 32,779 patients included in the analysis. There were three ICD studies, totalling 1,148 patients, with 170 ICD discharges in the fish oil group and 188 in the placebo group (OR 0.90; 95% CI 0.55-1.46). There were six sudden cardiac death studies, including 31,111 patients, with 147 deaths in the fish oil group and 191 in the placebo group (OR 0.81; 95% CI 0.52-1.25).
In the 11 studies, covering 32, 439 patients, that looked at the effect on all cause mortality, there were 797 deaths in the fish oil group and 865 in the placebo group (OR 0.92; 95% CI 0.82-1.03). There were 360 and 446 deaths from cardiac causes in the fish oil and placebo groups respectively (OR 0.80; 95% CI 0.69-0.92).
Therefore, it would appear that fish oil supplements do significantly reduce cardiac mortality. However, there is no significant benefit on all cause mortality and most interestingly no benefit on arrhythmias. The mechanism of action of fish oils is open to debate but anti-arrhythmic activity had been felt to be an important factor.
This is in contrast to the often-cited GISSI-Prevenzione trial, which showed a reduction in all cause and cardiac mortality primarily driven by a reduction in sudden cardiac death. It should also be remembered that this analysis was driven primarily by two trials, GISSI and JELIS, which were undertaken, on different patient populations, for secondary and primary prevention, respectively.
The positive effects of fish oils in cardiac disease have long been recognised and the recent NICE endorsement of fish oil supplements in post MI management has further raised their profile.
Leon, H, Shibata MC, Sivakumaran S et al. Effect of fish oil on arrhythmias and mortality: systematic review. BMJ 2009; 338:a2931doi10.1136/bmj.a2931Reviewer
Dr Peter Savill
GPwSI Cardiology, Southampton