"To our knowledge, this is the first study to document an improved postexercise heart rate with omega-3 supplementation," said James O'Keefe from the Mid America Heart Institute and the University of Missouri.
Omega-3 fatty acids have been linked to a wide-range of health benefits, including cardiovascular disease (CVD), good development of a baby during pregnancy, joint health, behaviour and mood, and certain cancers.
However, a recent meta-analysis claimed that there was no evidence linking omega-3 intake and improvements in heart health, conclusions that were quickly slammed by a UK-based fish group.
The new randomized, double-blind, placebo-controlled crossover trial, published in The American Journal of Cardiology (Vol. 97, pp. 1127-1130), looked at the effects of a daily supplement of docosahexaenioc acid (DHA) and eicosapentaeoic acid (EPA) on the heart rate (HR), HR variability, and HR recovery after exercise of 18 white men, average age 68, who had suffered a heart attack three months to five years before the start of the trial.
The omega-3 supplement was produced by Ocean Nutrition Canada, and formulated to contain 75 mg of EPA and 195 mg DHA. Subjects took three tablets per day, giving them a daily omega-3 intake of 810 mg. The placebo contained 50:50 olive and corn oil.
After four months of supplementation of placebo or omega-3, the researchers reported: "Our principle findings were that omega-3 fatty acids significantly decreased HR at rest, accelerated the return to a normal HR after standing and exercise, and increased HR variability in the high-frequency bad."
After omega-3 supplementation the researchers reported a 19 per cent decrease in HR one minute after exercising.
"The decrease in HR was accompanied by appropriate increases in stroke volume and ejection times," said O'Keefe.
Men with high heart rates when resting have increased risks of cardiovascular events, including heart attacks and even death, explained the researchers.
Interestingly, no changes in blood pressure, inflammatory markers, and blood vessel elasticity were recorded, as have been reported by other high-dose omega-3 supplementation trials.
No clear mechanism for the improvement could be identified by the scientists, and further mechanistic research is needed.
The size of the sample population is also very limited and large, more long-term studies are required before any solid conclusions can be drawn.
The risk of pollutants from oily fish, such a methyl mercury, dioxins, and polychlorinated biphenols (PCBs) have led to some to advocate a reduction in fresh fish intake, despite others advising that the benefits of fish consumption outweigh the risks.
Such conflicting views on fish intake have seen the number of omega-3 enriched or fortified products on the market increase as consumers seek omega-3s from 'safer' sources. Most extracted fish oil are molecularly distilled and steam deodorised to remove contaminants.
But fears about dwindling fish stocks have pushed some industries to start extracting omega-3s from algae. Indeed, companies such as Martek Biosciences and Lonza are already offering algae-derived omega-3 DHA as a dietary supplement.