As the name indicates, cod liver oil is derived from the liver of the Atlantic cod fish (Gadus morhua).1 As with many fish oils, cod liver oil is rich in omega-3 fatty acids, as well as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and has high concentrations of vitamins A and D.2 These rich concentrations of vitamins A and D distinguish cod liver oil from other fish oils. A tablespoon of cod liver oil contains 400% of the US Department of Agriculture’s recommended daily allowance (RDA) of vitamin A and 200% of the RDA for vitamin D.3
The compounds in cod liver oil are largely considered to be n-3 polyunsaturated fatty acids (n-3 PUFAs).1 PUFAs are also considered to be free fatty acids and have multiple health benefits, including acting as antibacterial, antifungal, and antiviral agents.1 In recent decades, PUFAs have attracted intense interest from researchers for these functions as well as for their anti-inflammatory effects on the cardiovascular and neurologic systems.
Cod liver oil first gained wide acclaim in the prevention and treatment of the bony malformation in children known as rickets.2 Through a series of widely disparate studies and publications, scientists were able to connect the issues of poor nutrition and lack of adequate exposure to sunshine as the key elements in the development of rickets and blindness.2
However, it took several hundred years to actually confirm the association of vitamins A and D deficiency, rickets, and xerophthalmia (often called night blindness).2,4 Vitamin A is essential for the process by which light is converted into electrical signals in the rod cells, cone cells, and photosensitive ganglion cells of the retina. By the middle of the 20th century, rickets in the United States was a rapidly disappearing disease.
With rickets fading from the mainstream of medicine in developed countries, scientists are currently focusing on the exciting potential of cod liver oil supplementation to control symptoms of mood and depressive disorders as well as dementia. In a large population study conducted in Norway, nearly 22,000 adults were followed for 2 years.5 The study examined a variety of health aspects and outcomes, one of which was the correlation of daily cod liver oil supplementation and the presence and degree of depressive symptoms. Retrospective data showed that patients consuming daily cod liver oil supplements were approximately 30% less likely to have symptoms of depression than those who did not use the supplemental fish oil. Similar studies agree with these findings.