Omega-3 fatty acids, the main component, reduce the activity of enzymes which damage cartilage cells. Professor Caterson of the university's School of Biomedicine says: "The data suggests that cod-liver oil has a dual mode of action, potentially slowing down cartilage degeneration and reducing factors that cause pain and inflammation."
There are many species of cod, but for commercial fishing the Atlantic cod (Gadus morhua) is what it's all about. It is a migratory marine fish with three dorsal and two anal fins, and a large head. It can be grey and green to brown, blackish of even red. Living in the ocean's bottom layers, the Atlantic cod can be found on both sides of the north Atlantic. They usually average three to four kilograms but can weigh up to 90kg, and can live for more than 20 years. They are slow fish, usually found in fairly shallow waters, and swim in large schools. Atlantic cod can be sold fresh, frozen, salted and smoked, or turned into sticks, blocks and fillets. They can also be used in fish meal, for cod-liver oil and in glue production.
* Cod farming - a growth industry - may offer a partial solution to the depletion of stocks, but there are environmental issues. Salmon farming has acquired a dubious reputation because of its use of chemicals used to control sea lice and the accumulation of toxins in the flesh. Farmed cod will be genetically different from their wild counterparts and the WWF has expressed fears about disease transfer to wild cod or harmful genetic interbreeding with escaped farmed fish.