What is the difference between fish oil and cod liver oil? Is one better than the other?

Answer:

Regular fish oil is pressed from the whole body of the fish, while cod liver oil is pressed from the liver of the fish. Both can be good sources of the omega-3 fatty acids DHA and EPA, but cod liver oil contains substantial, and in some cases, excessive amounts of vitamin A, as well as a good amount of vitamin D, which are not generally found in regular fish oil supplements. One type of oil is not necessarily better than the other, but which one you choose should be based on your nutritional needs and your reason for taking it.

Be aware that some "vitamin A" supplements that list cod or other fish as ingredients do not contain the omega-3s and vitamin D found in true cod liver oil.

Getting omega-3s
A typical recommended daily serving from either a fish oil or cod liver oil supplement can easily provide the daily intakes of EPA and DHA recommended by some countries (300 mg to 500 mg combined) and, if taken every day, slightly more than the amount provided by the American Heart Association's recommendation of one to two servings per week of fatty fish, such as tuna or salmon.

However, if you need higher, therapeutic doses of EPA and DHA (thousands of milligrams of EPA and DHA combined, as taken for lowering triglycerides, treating ulcerative colitis, depression or other conditions), fish oil supplements are a better choice. This is because the amount of cod liver oil you would need to consume in order to get these higher amounts of DHA and EPA will typically include excessive amounts of vitamin A. (See the Fish Oil Supplements Review for information about highly concentrated supplements that are similar to prescription fish oils, as well as our Top Picks among products).

Vitamins A & D
The amounts of vitamin A in the retinol form found in several cod liver oils tested by ConsumerLab have exceeded the daily requirements for adults, and exceeded daily Tolerable Upper Intake Levels for children and/or adolescents, above which there is a risk of adverse events. That being said, ConsumerLab has also identified products that contains lower amounts of vitamin A with a relatively high dose of EPA and DHA combined.

As to vitamin D, cod liver oils tested by ConsumerLab have tended to provide about 400 IU (10 mcg) of vitamin D per daily serving -- a good portion of the recommended daily intake of vitamin D for adults. Cod liver oil may be a good option for those who want to increase their intake of omega-3s but do not get enough vitamin D from their diets or sun exposure. (See our Top Picks among cod liver oils).