Written by in section: Medicine > Supplements
Medically Reviewed by Dr. Aj Thomas MS, MBA & Updated on Apr 3, 2016
Cod Liver Oil Supplement Benefits and Side Effects
Cod liver oil

Cod liver oil and Fish oil are two different types of fish based oil rich in Omega-3 fatty acids.

What is cod liver oil?

Cod liver oil is made from the livers of cod fish and has been used as a nutritional supplements for many centuries. It is rich in Omega-3 fatty acids that contain Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) which are essential fatty acids that our body needs to maintain good health.


What is difference between Cod liver oil vs Fish oil?

The Omega-3 in fish oil is going to be lot more in quantity in fish oil when compared to cod liver oil which delivers a lower dose of essential Omega-3 fatty acid. However, they compensate this by offering more Vitamin A and Vitamin D because these vitamins are stored in the liver of the fish from where cod liver oil is extracted.

If you are not having a balanced diet or taking any vitamin supplements, then cod liver oil might be a better option when compared to fish oil.

Read more about fish oil: Omega-3 Fish Oil Supplement Benefits and Side Effects


Vitamin A and Vitamin D complements each other and they more beneficial when taken together. Here are some benefits of each of them:

Vitamin A

It is important for maintaining healthy vision, healthy skin and neurological functions. It is a powerful antioxidant and it can reduce free radicals which reduces the overall risk of cancer.

It also can improve the immune system by stimulating the production and activity of white blood cells in the body. It is also helpful in regulating healthy cell growth and division.

Vitamin A toxicity: Vitamin A is a fat soluble vitamin, therefore, if you take in excess of this vitamin it will get stored in your body and this can be toxic (Hypervitaminosis A).


Vitamin D

Our body can make vitamin D when our skin is exposed to the sunlight, but for people who live places where there is not much sunshine, you may need to take vitamin D supplements. Modern lifestyles can also be one important facts for getting less vitamin D in your system.

Vitamin D is important for the absorption of calcium and phosphorous from the diet we eat. It is very important for maintaining healthy bones and teeth.

Vitamin D toxicity: A note of caution, before you start supplementing your diet with vitamin D, it would be a good idea to get yourself tested to see how much vitamin D is there in your body since vitamin D is also a fat soluble vitamin.

A blood test with 25-hydroxy vitamin D test is considered as one of the most accurate vitamin D test.


Is cod liver oil safe?

Pregnancy: Since cod liver oil contains vitamin A and D, it would be easy to overdose on these fat soluble vitamins if you are already eating a healthy balanced diet and getting enough sunlight exposure. Have too much vitamin A, retinol (Hypervitaminosis A) may increase risk of birth defects.

It is best consult with your doctor if are pregnant or breastfeeding before starting cod liver oil supplements.

Contamination: A lot of these Omega-3 producing fatty fishes contain high levels of Mercury, PCBs, heavy metals and other industrial toxins as contamination in their tissues. Like fish oil, manufactures have to purify these oils in order for it to be considered safe for human consumption. Unfortunately processing cod liver oil creates a new set of problems.


How is cod liver oil made?

Cod live oil can be manufactured by heat pressing or cold pressing after fermentation. Cheaper variants of cod liver oil may use Alaska Pollock as a substitute for the more expensive cod fish.


There are basically two types of cod liver oil based on how they are manufactured:

Processed Cod liver oil

Processed cod liver oil is also known as un-fermented cod liver oil. The cod liver is steam pressed to extract the oil, while this process is efficient in extracting the oil from the liver of cod fish, the high temperatures can damage the vitamin contents in the cod liver.

Manufactures may try to compensate this by adding synthetic vitamin A and D to the end product. Manufactures can also further process cod liver oil in order to purify it and remove toxins.


Fermented Cod liver oil (FCLO)

FCLO is made by fermenting the livers of cod fish. This was the traditional way of making cod liver oil before the industrial revolution.

To make cod liver oil by fermenting, large wooden barrels had to be filled with fresh cod livers and then seawater was added to the barrels.

The mixture is allowed to be fermented for up to a year and then later the cod liver oil is extracted from the fermented mixture by cold press.

Cold press does not damage the vitamin A and D in the liver of cod fish. The manufacturing process is comparatively more resource intensive and time consuming, there the end product is more expensive than processed cod liver oil.

In recent year there has been certain controversies regarding FCLO and its actual health benefits. More research and analysis is required at this point in order to support or object the use of FCLO.



Increasing consumer demands and over fishing has led to endangering many species of fishes in the oceans. Consumers should make sure that they buy from companies that have high moral and ethical values.

Consumer should prefer manufactures that take fishing sustainability seriously when it comes to where and how they source their raw materials.

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  • Last Reviewed on:Apr 3, 2016
  • Medically Reviewed by:Dr. Aj Thomas MS MBA
  • References:


    1. 25-hydroxy vitamin D test: MedlinePlus Medical Encyclopedia. https://www.nlm.nih.gov/medlineplus/ency/article/003569.htm.
    2. Rajakumar K. Vitamin D, Cod-Liver Oil, Sunlight, and Rickets: A Historical Perspective. Pediatrics. 2003;112(2):e132-e135. doi:10.1542/peds.112.2.e132.

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