Mother Was Right About Cod Liver Oil

George T. Griffing, MD


January 11, 2008

There are many stories of mothers forcing their children to take cod liver oil.

Centuries ago, northern Europeans used cod liver oil to protect them from the cold. It was made from the livers of Gadus morhua and other species of cod. Cod liver oil was said to relieve such complaints as rheumatism, aching joints, and stiff muscles.

At the beginning of the 20th century, scientists established that cod liver oil was antirachitic, and it became commonplace for mothers to give it to their children.[1,2]

It turns out cod liver oil contains large amounts of vitamins A, D, and omega-3 fatty acids, and the health benefits may go beyond rheumatism and rickets.[3]

Vitamin A is essential for the immune system, bone growth, night vision, cellular growth, testicular and ovarian function. Pharmaceutical preparations are used to treat acne vulgaris and keratosis pilaris and to treat acute promyelocytic leukemia.[4]

Vitamin D not only prevents rickets but is also important for muscle function and may prevent type 1 diabetes, hypertension, and many common cancers.[5,6,7,8]

Fish oils include the omega-3 fatty acids (O3FA), eicosopentanoic acid, and docosahexaenoic acid (EPA and DHA). Recent evidence supports the cardiac benefits of O3FA, beginning in 1999 with publication of the GISSI study, which showed reduction of mortality and sudden death.[9] Further data emerged from analysis of the Physicians Health Study, which showed a stepwise reduction in risk of sudden cardiac death based on blood levels of omega-3 fatty acids. Most recently, the Japanese EPA Lipid Intervention Study (JELIS) showed a reduction in coronary events. Sudden death was not affected, however, suggesting that the high fish intake in Japan may lower the baseline risk for this finding.[10]

The mechanism for fish oil protection has been speculated to be an improvement in lipids with a reduction in triglycerides and an increase in HDL and a direct membrane stabilizing effect of omega-3 fatty acids.

The data are strong enough that European and American cardiac societies have incorporated EPA and DHA into their recent treatment guidelines for cardiac diseases.

Cod liver oil is not for everyone, however. Cod liver oil is probably best avoided by pregnant women, asthmatics, and people taking anticoagulants such as warfarin.

It is wise to remember to listen to your mother -- at least about cod liver oil.

That's my opinion. I'm Dr. George Griffing, Professor of Medicine at the St. Louis University and Editor in Chief of Internal Medicine for eMedicine.

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