Fish oil is found in species of oily fish, such as tuna, halibut, and salmon. It can be obtained by eating fish flesh or through processed supplements, either in liquid or pill form. Cod liver oil is a type of fish oil made from the liver of a fish called cod. It is generally only found in nutritional supplements since people do not often eat fish livers. Cod liver oil and fish oil are used as dietary supplements often because they contain Omega-3 fatty acids.
Omega-3 fatty acids help decrease swelling and pain, acting as anti-inflammatory agents. The body cannot produce these fatty acids on its own, so it must rely on outside sources, such as fish oil, to obtain them. Since cod liver oil and fish oil contain Omega-3 fatty acids, they are often suggested to help arthritis suffers. Cod liver oil, in particular, is frequently suggested for this purpose, but all fish oil seems to work. Fish oil is also thought to help prevent heart disease and stroke because it aids in thinning the blood, preventing clotting.
Cod liver oil is made only from the livers of cod. A type of bottom-dwelling fish, cod live in the cold water of the Atlantic and parts of the Pacific oceans. Unlike most fish used for fish oil, cod is considered a white fish, not a oily fish. This is why the oil is supplied from its liver rather than its flesh.
Another difference between cod liver oil and fish oil is the amount of vitamin A present in the supplements. Fish oil in general contains very little vitamin A because that vitamin is not found in the fish flesh. Vitamin A is found in the liver, however, so cod liver oil contains high amounts of vitamin A, particularly when taken in the liquid form. Although vitamin A is helpful and necessary in small doses, in large doses it can cause bones to weaken and birth defects. There is also a concern when taking cod liver oil of contaminants since the oil is made from an organ which filters toxins.
As with any supplement, both cod liver oil and fish oil should be taken in moderation. High doses can increase the risk of bleeding and may impede the proper control of blood sugar in diabetic patients. Fish oil also may interact with high blood pressure medication by further decreasing blood pressure, causing it to drop to dangerously low levels. Conversely, some birth control and weight loss pills may decrease the effectiveness of fish oil.