Recent scientific evidence points to a significant reduction in the incidence of heart disease in those who consume large amounts of fish. In particular, it appears that it is the omega-3 fatty acids present in fish that are responsible for this reduction.
In countries such as Ireland and Japan, and Iceland, where per capita fish consumption is very high, deaths attributable to heart disease are relatively low compared to other developed countries such as the USA and United Kingdom.
A study conducted in 2002 and published in the Journal of the American Medical Association , used data from the Nurses Health Study of more than 80,000 women to determine the impact of fish consuption on coronary heart disease.
The researchers found that compared to those who rarely consumed fish, those women who consumed more than 5 servings of fish a week were 34% less likely to develop heart disease and 45% less likely to die as a result. The authors concluded that “Among women, higher consumption of fish and omega-3 fatty acids is associated with a lower risk of CHD, particularly CHD deaths.”
Similar benefits of frequent fish consumption have been found in men. A large study published in the Journal of the American Medical Association in 1998 used data from the Physicians Health Study which involved more than 20,000 US males aged between 40 and 84. The researchers found that the incidence of sudden cardiac death was reduced by 52% in men who consumed fish at least once a week compared to men who ate fish less than once a month. The full results of the study are shown in the graph to the right.
In a randomized control trial conducted in 1999 by Italian researchers, 11,324 heart attack survivors were randomized to receive a placebo, or either 850mg of omega 3 fatty acids, 300mg of Vitamin E, or both. After following the participants for 3.5 years the group given omega-3 fatty acids experienced a 20% reduction in death from all causes and a 45% reduction in sudden death compared to the control group.
Research has typically found that the heart benefits of fish consumption are stronger for oily fish rather than lean fish. This suggests that it is the omega 3 fatty acids found in fish oil that are responsible for the heart benefits of fish.
The mechanisms by which fish oil reduces the risk of heart disease are thought to be through a reduction in blood triglyceride levels, reductions in blood pressure, and perhaps most significantly, through a reduction in cardiac arrhythmias which can lead to sudden cardiac death. Evidence of this comes from animal studies in rats and dogs where fatal ventricular arrhythmias have been prevented by supplementation of omega 3.
In humans, studies have shown that heart rate variability in survivors of myocardial infarction is increased when fish or fish oil supplements are consumed. Heart rate variability is a strong predictor of mortality in heart attack survivors with low heart rate variability associated with a much higher rate of sudden cardiac arrest due to arrhythmias. Long term fish oil consumption may also reduce the rate of arterial plaque development although evidence from clinical studies that fish oil can prevent atherosclerosis has been mixed.
The American Heart Association (AHA) recommends eating at least two servings of fish a week to reduce the risk of heart disease. Individuals should aim to consume around 1.2g of omega 3 fatty acids a day. This corresponds to 4 standard strength fish oil capsules each day in the absence of any dietary sources of omega 3. Most people should be able to consume between 500-800mg of omega-3 per day on average with one or two omega-3 capsules making up the remainder of the days requirement.
Abundant sources of omega-3 include (grams of omega-3 per serving in brackets): tuna (0.3g), salmon (1.2g), cod (0.2g), flounder (0.5g) and halibut (0.9g). Non-fish sources of omega-3s include: walnuts (2.5g), flax seeds (1.6g), soy beans (0.5g), canola oil (1.2g), chia seeds (4.9g), and beef and lamb (particularly from grass fed animals).
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