A 2002 statement in the American Heart Association journal "Circulation" says that numerous studies have demonstrated that two omega-3 fatty acids present in cod liver oil and fish oils like salmon oil can help to reduce heart disease both in healthy individuals and people with pre-existing cardiovascular disease. While cod liver oil and salmon oil are both sources of the two essential omega-3 fatty acids, they possess them in different ratios and amounts. Cod liver oil and salmon oil also differ in origin, vitamin content and risk of toxicity.
Omega-3 Fatty Acids
Both cod liver oil and salmon oil are rich in two omega-3 fatty acids considered essential for health: EPA, or elcosapentaenoic acid, and DHA or docosahexaenoic acid. Cod liver oil has more DHA than EPA and salmon oil has more EPA than DHA, although in terms of sheer amount, salmon oil contains nearly twice the EPA and DHA of cod liver oil.
The American Heart Association recommends one gram each of EPA and DHA per day for people with documented coronary heart disease and 2 g to 4 g per day of each for people with high cholesterol. Of course, it also advises doing so under a doctor's supervision. While the AHA recommends people without either of these conditions eat two servings of fish per week, preferably fatty, oily fish like salmon, in order to obtain essential omega-3 fatty acids, it does not recommend obtaining that weekly allowance from supplements without a doctor's recommendation and supervision.
One tablespoon of cod liver oil contains around 1,360 IU of vitamin D, about the same amount of as 1.5 pounds of sardines or fatty herring. Salmon oil has only 1/5 that amount. Vitamin D is helpful in building strong bones and muscles and helps support the nervous system. Cod liver oil is also three times higher in vitamin A than salmon oil. Vitamin A supports growth and strong immune function and eyesight.
The American Heart Association lists salmon as one of the five most commonly eaten fish with a low mercury content. According to the AHA, fresh or frozen salmon may have about 0.01 parts per million of mercury, whereas cod may have 0.11 parts per million. Made from the liver of the fish, cod liver oil is even more likely than other fish oils to contain any PCBs or other environmental toxins to which the fish is exposed in the water, as these are filtered by the liver, where they tend to collect.