People who eat fish a couple of times a week have fewer heart attacks than people who never eat fish. Researchers at the Japanese National Center of Neurology and Psychiatry in Kodaira may have discovered how fish protects the heart and blood vessels. They believe that eating fish protects the heart muscle from the effects of stress.
Fish protects heart against stress
Stress raises the likelihood of contracting cardiovascular disease and eating fish reduces it. This is probably because of the fatty acids found in fish: EPA [structural formula shown here] and DHA. If you give people supplements containing fish fatty acids for longer than 12 weeks their heart rate goes down [Circulation. 2005 Sep 27; 112(13): 1945-52.] and the likelihood of them developing cardiovascular problems as well. That’s why the Japanese wondered whether these two factors – stress and fish consumption – could cancel out each other’s effect on the heart muscle.
The researchers did an experiment with 12 students who ate more than 70 g fish four times a week, and 13 students who ate less than 70 g fish not more than twice a week. The subjects had to keep subtracting 13 starting from 5000 [5000 – 4987 – 4974 etc.] and the researchers told them whether their answers were correct or not. At the same time the subjects’ heart functioning was monitored.
The researchers discovered that a high-fish diet had no effect on how difficult or unpleasant the subjects found the test. So the amount of mental stress was the same in both groups.
Among the group that ate large amounts of fish, the systolic blood pressure [pressuring during the heart beat; SBP], the average blood pressure [MBP] and the diastolic blood pressure [pressure between two heart beats; DBP] rose by less than among the subjects that ate little fish. The heart rate increased less in the fish eaters than in the other group.
The pulse wave velocity [an indicator of the stiffness of the blood vessels; PWV] also rose less than in the low fish eating group.
Fish protects heart against stress
The Japanese conclude that a diet rich in fish normalises the heart muscle under conditions of stress. They note, however, that the fish eaters’ diet differed from that of the other group in a number of ways. “A group difference in fish-eating habit was a salient feature, but such a dietary pattern was accompanied by modulation in other food categories, including a higher intake amount of fruits, algae, and vegetables.”
Nevertheless, the Japanese maintain that it’s the fish that is responsible for the cardiovascular stress protective effect. “These findings suggest a possible physiological mechanism that may explain why frequent fish consumption reduces coronary heart disease risk”, they write.
Effect of fish oil on heart rate in humans: a meta-analysis of randomized controlled trials.
Mozaffarian D, Geelen A, Brouwer IA, Geleijnse JM, Zock PL, Katan MB.
Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA. firstname.lastname@example.org
The effect of fish oil on heart rate (HR), a major risk factor for sudden death, is not well established. We calculated this effect in a meta-analysis of randomized, double-blind, placebo-controlled trials in humans.
METHODS AND RESULTS:
Randomized trials of fish oil that evaluated HR were identified through MEDLINE (1966 through January 2005), hand-searching of references, and contact with investigators for unpublished results. Two investigators independently extracted trial data. A pooled estimate was calculated from random-effects meta-analysis. Predefined stratified meta-analyses and meta-regression were used to explore potential heterogeneity. Of 197 identified articles, 30 met inclusion criteria. Evidence for publication bias was not present. In the overall pooled estimate, fish oil decreased HR by 1.6 bpm (95% CI, 0.6 to 2.5; P=0.002) compared with placebo. Between-trial heterogeneity was evident (Q test, P<0.001). Fish oil reduced HR by 2.5 bpm (P<0.001) in trials with baseline HR > or =69 bpm (median) but had little effect (0.04-bpm reduction; P=0.56) in trials with baseline HR <69 bpm (P for interaction=0.03). Fish oil reduced HR by 2.5 bpm (P<0.001) in trials with duration > or =12 weeks but had less effect (0.7-bpm reduction; P=0.27) in trials with duration <12 weeks (P for interaction=0.07). HR reduction with fish oil intake did not significantly vary by fish oil dose (range, 0.81 to 15 g/d), type of HR measure, population age, population health, parallel versus crossover design, type of control oil, or study quality by Delphi criteria (P for interaction >0.25 for each).
In randomized controlled trials in humans, fish oil reduces HR, particularly in those with higher baseline HR or longer treatment duration. These findings provide firm evidence that fish oil consumption directly or indirectly affects cardiac electrophysiology in humans. Potential mechanisms such as effects on the sinus node, ventricular efficiency, or autonomic function deserve further investigation.
PMID: 16172267 [PubMed – indexed for MEDLINE]