For years people have been taking cod liver oil as a food supplement. It is simply the oil processed from the Atlantic cod fish's liver and other fatty areas after the fish is caught and processed for its flesh and liver. 

The oil from the cod fish and in particular its liver has vitamins A and B and very high levels of docosahexaenoic acid also known as DHA, omega three fatty acids and eicosapentaenoic acid also known as EPA. 

Generally cod liver oil is placed in gelatin capsules for swallowing since the oil does not have a good taste as a general rule to those that ingest the oil directly.

Vitamin A's importance is for the maintenance of one's immune system, for growth and development, and one's vision. Vitamin B assists in cell metabolism. Ordinarily young children deficient in vitamins A and B take cod liver oil supplements. However, the elderly also take the supplement as well depending upon their physical condition and needs.