(30-12-05) Meta Analysis Confirms Fish Oil Lowers Heart Rate

There is a substantial body of evidence from animal and human studies that alpha-linolenic acid and the long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFAs) have anti-arrhythmic effects. These properties appear to account for the significantly lower chance of sudden cardiac death reported in several studies. However, the effects of fish oil or n-3 LC-PUFAs on heart rate, another electrophysiological property of the heart, have been mixed. Increased heart rate is associated with increased risk of cardiac mortality from various cardiac causes.

To evaluate the results from various clinical trials measuring heart rate in a systematic and controlled way, Dr. Dariush Mozaffarian and colleagues at the Harvard School of Public Health, Boston, USA, conducted a meta-analysis?a combined statistical analysis of many studies?of randomized clinical trials of fish oil published from 1996 through early 2005. The investigators excluded studies conducted in organ transplant patients, those not having a placebo control, studies having a co-intervention that could not be separated from fish oil, or were less than 2-weeks duration.

Thirty trials met the inclusion criteria, including data from two unpublished trials. These studies represented 1,678 individuals treated with fish oil or a placebo for 27,615 person-weeks. Median age of participants was 54 years (range 23-68 years) and the median dose of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) was 3.5 g/day for a median of 8 weeks (range 4-52 weeks). The primary outcome was change in heart rate resulting from fish oil treatment.

The overall pooled estimate of change in heart rate was a decrease of 1.6 beats/min. (95% CI 0.6 to 2.5, P=0.002). Heterogeneity among trials was statistically significant, with reduction in heart rate with fish oil being significantly greater in studies whose participants had baseline heart rates equal to or greater than 69 beats/min.(P for interaction=0.03). In those studies, fish oil decreased heart rate by 2.5 beats/min (95% CI, 1.4 to 3.5; P<0.001). In trials lasting 12 weeks or longer (P for interaction=0.07), fish oil reduced heart rate by 2.5 beats/min. (95% CI, 1.1 to 4.0, P=0.001). There was little evidence of a dose-response effect, as reduction in heart rate was not significantly different between higher and lower doses compared with the placebo.

As the authors commented, the overall effect of fish oil on heart rate was small, 1.6 beats/min., but on a population basis, such a change in cardiac risk can have significant impact on health. According to one estimate, this reduction in heart rate might correspond to a 5% reduction in sudden death. Because there was no apparent benefit associated with higher versus lower doses, these collective findings suggest that modest intakes of fish oil, such as would be obtained from eating fatty fish twice a week, may have beneficial effects on heart rate and presumably lower risk of cardiac mortality. Now that?s something to make the heart throb.

Mozaffarian D, Geelen A, Brouwer IA, Geleijnse JM, Zock PL, Katan MB. Effect of fish oil on heart rate in humans. A meta-analysis of randomized controlled trials. Circulation 2005;112:1945-1952.

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