Cod liver oil is, as the name suggests, derived from the liver of the cod fish. It is very rich in vitamin A and vitamin D, and also has high levels of omega-3 fatty acids, including EPA and DHA.
The Vikings were probably the first to realise the benefits of cod liver oil, and regularly consumed it during long, cold winters. By the 1700s, physicians were using it to rub into muscle sprains, and then later prescribing it to be taken internally. At the time, vitamins A and D were unknown, as were omega-3 oils, but the oil was widely known to help relieve joint stiffness. It was also used effectively as a wound dressing.
Today, we know that cod liver oil as a supplement helps to support joints due to its vitamin content, and also because it reduces enzyme activity associated with cartilage pain.
We also now know that the omega-3 fatty acids in cod liver oil help to boost eye health and prevent macular degeneration, and that they promote healthy skin and heart health. Omega-3 acids are highly concentrated in the brain and appear to be vital for good cognitive health.