Cod liver oil is a nutritional supplement derived from liver of cod fish.
As with most fish oils, it has high levels of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Cod liver oil also contains vitamin A and vitamin D. It has historically been taken because of its vitamin A and vitamin D content.
It is commonly given to children, because vitamin D has been shown to prevent rickets and other symptoms of vitamin D deficiency.