Cod liver oil is a nutritional supplement derived from the liver of Cod fish. It has high levels of the omega 3 fatty acid and very high levels of vitamin A and vitamin D. It is widely used to ease the pain and joint stiffness of arthritis as well as other health benefits. Cod liver oil has been clinically proven to have a positive affect on the heart, bones and the brain. It also helps nourish skin, nails and hair. Also the use of cod liver oil during pregnancy is associated with lower risks of diabetes in the offspring.