Cod Liver Oil

Cod liver oil is the only nutritional supplement that has stood the test of time. Cultures in Northern Europe realized the health benefits of consuming fish oil thousands of years ago. As the world changed and developed, as empires rose and fell, the understanding that cod liver oil was healthy persisted. Even before clinical trials and nutritional sciences developed, unconnected populations noticed that cod liver oil improved health, strength, and vitality. The importance of this should not be overlooked. Despite no understanding of nutrition or an ability to control variables, cod liver oil was consistently observed as something that promoted health. It was seen as a medicine by some, elixirs by others. Today, we see it as a health supplement.

It was not until the 1900s when developments in science were able to explore nutrition, that cod liver oil was really put under the microscope. The nutrients in cod liver oil were finally beginning to be understood, but even today there are aspects of cod liver oil that are not fully realized.

Cod Liver Oil

Cod liver oil is, as the name suggests, the oil from cod livers. There are many members of the cod (or Gadidae) family, all of which have oil-rich livers. Historically, Atlantic Cod (Gadus morhua) was used to make cod liver oil and it was found in abundance in North European waters and the North-Eastern coast of North America. Throughout history, the livers of cod were fermented in high-salt conditions. This would break down the livers and the oil would float to the top. As food science developed throughout the 1900s, traditionally produced cod liver oil from Atlantic Cod became harder to find. It has been and was replaced by conventional cod liver oil, which fills health shops today. This cod liver oil is made with a variety of related fish and is processed differently. These differences will be discussed later on.

By Hans-Petter Fjeld

Why cod liver oil is healthy

Cod liver oil is healthy because it is rich in omega-3 fatty acids, vitamin D, vitamin A, and various other nutrients. Omega-3 fatty acids and vitamin D in particular are not found in many foods, which makes rich sources of these nutrients very important. Your skin can synthesize vitamin D when exposed to sunlight. However, in Europe, particularly in winter, months can pass without any significant sun exposure. This makes dietary sources of vitamin D even more important during the winter months. These nutrients play a very important role in a variety of functions in the body and are essential to maintaining a healthy lifestyle. You can find more information on the specific benefits of cod liver oil here.


Cod are relatively high on the food chain. This means that environmental pollutants will become concentrated in their bodies. Oil-soluble contaminants are particularly concerning for cod liver oil. Large marine animals are known to contain dangerous amounts of heavy metals such as mercury, but marine oil is also high in PCBs and dioxins. Heavy metals, PCBs, and dioxins are powerful carcinogens, and their content in foods is heavily regulated, although it is poorly enforced. There are various methods for removing these contaminants, some of which are uniquely developed by manufacturers. Screening of these contaminants should be done prior to sale, but disingenuous manufacturers may not screen for these contaminants.

accumulation of contaminants in cod liver oil
Accumulation of toxins

Old VS New

There are some differences between the cod liver oil that was seen as an elixir a thousand years ago, and what you find now. Traditional cod liver oil released oil from the livers through bacterial action in seawater. The high salt concentration and lack of oxygen create an environment that favors lactobacillus bacteria. These bacteria feed on the glycogen in the cod livers and produce acid. This acid would make the environment increasingly hostile for other bacteria populations. Eventually, as the carbohydrates in the liver are consumed by acid-producing bacteria the environment becomes inhabitable and renders the product safe to consume. This process is very similar to other salt fermented meats found throughout the globe. There is evidence that this fermentation has an enriching effect on cod liver oil. Acid-producing bacteria such as lactobacillus do produce beneficial nutrients. Research in this area is somewhat limited.

A conventional cod liver oil is much more heavily processed. There are variations to the process, but typically the oil is heated, undergoes alkali treatment, filtered, and concentrated. The oil will have high concentrations of the omega-3 fatty acids EPA and DHA, but these will have been chemical changes to facilitate the extreme processing. Vitamin D has often been added into the oil as well.

Cod liver oil quality

Cod liver oil quality can vary dramatically. The omega-3 fatty acids are delicate and so vulnerable to oxidation. Additionally, screening of contaminants, the chemical form of fats, and vitamin content all play into the quality of cod liver oil. Environmental factors are increasingly important factors too. Cod populations are quite heavily regulated in some parts of the world, but they remain relatively low.


Unlike many health supplements today, cod liver oil is not a fad. Consistently throughout history, it has been recognized for its significant impact on health. Through modern research methods, it is now known that these benefits primarily come from vitamin D and omega-3 fatty acids, which the oil is rich in.

Cod liver oil can be produced in a variety of ways in the modern world, and quality can sometimes be hard to discern. Industrial contaminants pose health risks, and various production methods can impact the quality of the oil. Understanding cod liver oil and how it is processed can be the difference between getting a health-promoting elixir and a carcinogenic toxic oil.


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