What to look for in a cod liver oil

What to look for in a cod liver oil

There are an untold number of cod liver oil brands, and so picking the one for you can be hard. Some decisions are subjective. For example, the source of the cod is important to some, but not everyone. Other aspects though, are more objective. For example, no one wants a rancid oil. It is these objective aspects that we will briefly go into in this post, in particular, what to look for in laboratory tests.


Basic information

This information should always be on the label of a cod liver oil. With both the omega-3 levels and vitamin levels, it is not always a case of more is better. The quality can vary dramatically for both, but that is for another discussion.

Omega -3 – Omega-3 content should be expressed as EPA and DHA values. Cod liver oil has EPA values in the region of 13mg/g and DHA values of 7mg/g. There is always some natural variation, but levels that vary greatly from these figures mean it is authentic cod liver oil. The oil is either concentrated, had extra synthetic omega-3’s added and/or are a blend of a variety of fish oils.

Vitamin levels – Vitamins should be expressed as vitamin D3 and vitamin A. These are the 2 important vitamins in cod liver oil. If vitamin D is represented without a ‘3’ after it, it is possible that synthetic vitamin D2 has been added to the oil, which is inferior. Vitamin D3 and A levels vary quite dramatically, and in many oils both these vitamins are added after processing, and are synthetic.


Quality information

This information will not be included on labels; however, the manufacturer should have access to it.

Peroxide value – When fats are exposed to air, they break down into peroxides. Peroxides are undesirable, but all oil will contain small amount of peroxides, including olive oil and coconut oil. Some food oils are allowed to have peroxide values of 10meq/kg, but for cod liver oils, the levels should be less than 5meq/kg. A higher peroxide value represents more damage to the oil.

Anisidine value – After fats are broken down into peroxides, they undergo further reactions and form anisidine compounds. The anisidine values are another indicator that is oil is damaged. Anisidine values should be below 20meq/kg.


Environmental pollutants

This information will also not be on the label, but again, the manufacturer should be able to provide it.

PCB’s/ dioxins/ furans – These are a big problem for cod liver oil. These toxins accumulate up the food chain, and with cod being high in the food chain, their oil is at risk of containing toxic amounts of these toxins. The levels of these toxins are always combined ad represented as a toxic equivalent value (TEQ). It is important to realise that these can be easily mis-represented. The full value should be WHO-PCDD/F-PCB, which is a combination of all the toxins. There are also tests results just for WHO-PCDD, which is measured with the same units, but doesn’t contain all the toxins in the test.

The maximum allowed levels for these toxins set by European Commission is 6.0ng/kg fat. Cod liver oils made or sold outside of the EU will have different regulations to this.



There will of course be other things that manufacturers test for, however, the point mentioned here are some of the most important. You need to know the omega-3 content, vitamin content (and form). You also need to make sure the oil has not oxidised, and isn’t too high in environmental pollutants. It may be that you have to ask manufacturers for some of this data, but it should be readily available to them. Please do have a look at our fermented cod liver oil test result data to see how it compares.

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