Fish oil is packed full of omega-3 polyunsaturated fatty acids (PUFAs), a type of unsaturated fat which is well known for its anti-inflammatory action. Inflammation is associated with many chronic illnesses. Fish oil is known to have a beneficial action on the cardiovascular system, in the prevention of cardiovascular disease and cardiac events (heart attack and stroke). 

The use of fish oil, as a health supplement for the prevention of cardiovascular disease, originated from studies performed on the Inuit people of Greenland. These people had lowered incidences of ischemic heart disease, thought due to their diet - comprising mostly of whales, seals, fish and sea birds. Health checks on this population of people showed lower platelet counts, a higher amount of omega-3 PUFA in the membranes of platelets, a longer time for clot formation and a lipid profile with a lesser potential to form atherosclerosis.

It was hypothesis the reduced heart disease risk profile was due to the diet, which provided higher amounts of omega-3 PUFAs - EPA and DHA. This hypothesis initiated decades of studies, trials and observations demonstrating the cardiovascular protective effect of fish consumption and omega–3 PUFA in supplement form.

What are Omega-3 fatty acids?

Omega-3 fatty acid contains ALA (α-linolenic acid), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). ALA is an essential fatty acid, meaning it is required by the body but cannot be made in the body and therefore must be provided through the diet. ALA can be provided from consuming products obtained from the sea (fish) and plant-based foods such as flaxseeds, walnuts and canola oil.

EPA and DHA are not essential as they can be made from ALA. However, the pathways for this to happen is inefficient in the human body and so to have a beneficial health effect, EPA and DHA is best obtained from marine sources. Fish oil and fish will give direct sources of EPA and DHA.

What does this mean for heart health?

Omega 3's have been shown through many studies to offer positive health benefits. Some of these include:

• Reduce triglycerides - a high level of triglycerides in the blood can increase the risk of heart disease
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• Reduces levels of inflammatory mediators
• Decrease the potential for plaque vulnerability and prevent its progression
• Improve endothelial dysfunction – endothelial dysfunction is a condition where the inner lining of the small arteries fail to perform important functions
• Reduce blood pressure - hypertension is associated with cardiovascular disease
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• Reduce resting heart rate
• Anti-thrombotic (at high doses -15g/day) reducing the potential for blood clot formation

Omega-3 PUFAs may also:

• Reduce heart rhythm problems (arrhythmias) – when the electrical impulses that coordinate the heartbeats are not working well and results in the heart to beating too fast, too slow or irregularly
• Improve myocardial efficiency
• Improve left ventricular diastolic filling
• Reduce vascular resistance

Intake and sources of EPA and DHA

Fish in the diet

Both wild fish sourced from the ocean and those which are farm-bred provide EPA and DHA.

Fish also offer other nutritional benefits, being high in protein, low in saturated fat and containing many micronutrients needed in the diet such as vitamin D, vitamin B12, selenium, potassium and magnesium.

Best fish to choose include: salmon, sardine, Atlantic mackerel, cod, herring, and trout. Aim for at least 2 meals containing fish per week -
grilled, broiled, or baked.

Contamination

Higher trophic fatty fish such as shark, swordfish and king mackerel may be contamination with methyl mercury and other pollutants (dioxins and polychlorinated biphenyls - PCBs). The amount of toxins depends on the type of fish and where it is caught. Vulnerable populations such as pregnant women and those trying to fall pregnant, breastfeeding women and children should avoid consuming these fish.

Supplementing with a good quality fish oil can alleviate any concerns or for those who just don’t like eating fish. Other sources of EPA and DHA include krill oil, cod liver oil, algae oils, walnuts, chia seeds and foods which have been fortified with omega-3 fatty acids.

Fish oil supplements and bleeding issues

Many people take fish oil capsules for cardiovascular health and lowering cholesterol, amongst many other beneficial reasons, but there are often concerns over whether supplemental fish oil consumption can cause bleeding during important medical procedures. 

Robust evidence to-date showed fish oil supplementation does not lead to increase peri-operative bleeding (1).

Some studies have not been so positive on the benefits of omega-3. This does not necessarily mean that fish oil supplements are ineffective, but more to do with the effect was not beneficial in the context in which it was tested.

The bottom line

Most studies confirm higher intakes of omega-3 PUFAs, either from fatty fish or from supplements is likely to lower risk for cardiovascular disease when taken for long periods of time. 

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References

Omega-3 Fatty Acids and Cardiovascular Disease: Are There Benefits? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5067287/

Fish, a Mediterranean source of n-3 PUFA: benefits do not justify limiting consumption https://pubmed.ncbi.nlm.nih.gov/26148923/

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/trophic-levels

https://www.mayoclinic.org/diseases-conditions/heart-disease/in-depth/omega-3/

https://www.mayoclinic.org/diseases-conditions/heart-arrhythmia/symptoms-causes/syc-20350668

https://www.ahajournals.org/doi/full/10.1161/circulationaha.106.660639

https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/triglycerides/art-20048186

(1) Fish Oil and Peri-operative Bleeding: Insights from the Omega-3 Fatty Acids for Prevention of Postoperative Atrial Fibrillation (OPERA) Randomized Trial