What does Fish Oil and Cod Liver Oil (EPA - DHA) do?

Oil from fish contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); both are omega-3 fatty acids.

Most fish oil supplements are 18% EPA and 12% DHA, or a total of 30% omega-3. These omega-3 fatty acids, unlike the omega-3 fatty acid found in flaxseed oil and other vegetable oils (such as alpha linolenic acid), keep blood triglycerides in check (high triglycerides are generally linked with increased risk of heart disease) and may inhibit the progression of atherosclerosis.¹ EPA and DHA keep blood from clotting too quickly.

EPA and DHA also have anti-inflammatory activity. As a result, fish oil is used to help people with various inflammatory conditions, such as Crohn’s disease² and rheumatoid arthritis.³ The anti-inflammatory effects of EPA and DHA may also account for the findings of some reports that show fish oil supplementation helps some people with kidney diseases^{4 5 6} and may help protect against chronic obstructive pulmonary disease.⁷

The omega-3 fatty acids in fish oil help to balance the omega-6 fatty acids, which are found mostly in vegetable oils. When these two groups of fatty acids are out of balance, the body releases chemicals that promote inflammation. People appear to produce more of these inflammatory chemicals when experiencing psychological stress (e.g., academic examinations). With a fatty acid imbalance, inflammatory response to stress appears to be amplified.⁸

Prostaglandins are hormone-like substances produced within the body that regulate dilation of blood vessels, inflammatory response, and other critical processes. Omega-3 fatty acids are needed for prostaglandin formation. Probably as a result of their effect on prostaglandins responsible for blood vessel dilation, a double-blind trial found that omega-3 fatty acids from fish oil helped to treat people with Raynaud’s disease.⁹

Schizophrenia is linked with abnormalities in fatty acid metabolism, and preliminary research suggests that fish oil supplementation may be helpful to people with schizophrenia.¹⁰ However, a double-blind study that used 3 grams per day of eicosapentaenoic acid failed to demonstrate any benefit for patients with chronic schizophrenia.¹¹

DHA is essential for vision in infants. Researchers are now studying this relationship to better understand how much DHA is needed.

EPA and DHA also modulate immune function,¹² probably as a result of their effect on prostaglandin production. Perhaps as a result of this effect, fish oil has helped prevent some types of cancer in animals^{13 14 15} and humans,¹⁶ although this evidence remains preliminary.

Preliminary evidence also shows that omega-3 fatty acids from fish oil may help regulate the rhythm of the heart. EPA and DHA have been reported to help prevent cardiac arrhythmias.¹⁷