Cod liver oil is widely taken to ease the pain and joint stiffness associated with arthritis,and has also been clinically proven to have a positive effect on heart, bone,and brain,as well as helping to nourish skin,hair, and nails.
Cod liver oil and fish oil are similar, but cod liver oil has much higher levels of vitamins A and D. Many adults do not meet the RDA for Vitamin D.

Cod liver oil may be an effective complementary measure for long-term treatment of multiple sclerosis.
Use of cod liver oil during pregnancy is associated with lower risk of Type I diabetes in the offspring.This effect was found only in mothers taking cod liver oil, not in mothers taking multivitamin supplements. Cod liver oil taken by nursing mothers improves the breast milk by increasing the amount of fatty acids, which promotes brain development, and the amount of vitamin A, which helps prevent infections, but the level of vitamin D is unchanged.
A Norwegian study of more than 68,000 women reported that female cancer patients who took daily cod-liver oil supplements had significantly reduced mortality (25% for all cancers, 45% for lung cancer).

Cod liver oil is a It has high levelsnutritional supplement derived from liver of cod fish.  of the omega-3 fatty acids, EPA and DHA, and very high levels ofvitamin A and vitamin D. It is widely taken to ease the symptoms of arthritis and for other health benefits. It was once commonly given to children, because the high levels of vitamin D in cod liver oil have been shown to prevent rickets.