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Topic: What seafood contains

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The Institute of Marine Research monitors the levels of nutrients and unwanted substances in seafood and studies their impacts on our body. 

We also do research into how food from the oceans can contribute to global food security. Amongst other things, food security means having safe and nutritious food available at all times. In other words, we must have enough food to feed the world’s population, and it must contain the right nutrients.

Seafood contains nutrients such as omega-3 fatty acids, vitamin D, iodine and selenium. These nutrients are not found in many other foods.

Nutrients in seafood

Fish and other seafood are a source of high-quality proteins. Seafood also contains marine-derived omega-3 fatty acids that our body struggles to make itself.

Fatty fish is a source of vitamin D, while lean fish like cod is one of the best sources of iodine within the Norwegian diet.

Omega-3 fatty acids

There are two main types of omega-3 fatty acids in our diet.

Plant-derived omega-3 fatty acids are mainly found in plants and farmed meat. The highest levels are found in certain plant oils.

Marine-derived omega-3 fatty acids are almost exclusively found in fish and other seafood. This is one of the reasons why the health authorities recommend including seafood in our diets. Fatty fish is especially rich in omega-3 fatty acids. Cod-liver oil and other fish oils also contain high levels of marine-derived omega-3 fatty acids.

It has been documented that the marine-derived omega-3 fatty acids EPA and DHA can reduce the risk of cardiovascular disease when consumed in our food. (FIND OUT MORE ON OUR PAGE ON HEALTH).

Plant-derived omega-3 can be converted into these fatty acids in our body, but the process is inefficient.

Omega-6 fatty acids

Linoleic acid is an essential omega-6 fatty acid that is important for our skin, mucous membranes and cells. Our body cannot produce linoleic acid itself, so we must consume it in our food.

Omega-6 fatty acids are mainly found in plants and in foods made from farmed animals. Plant oils such as soybean oil, maize oil and sunflower oil are particularly rich in omega-6 fatty acids.

Modern agriculture has increased the omega-6 levels in many types of food, including meat, eggs and dairy products. With our modern diet, it isn’t difficult for us to obtain enough omega-6; in fact, the reverse is true. Recent research indicates that a high ratio of omega-6 to omega-3 fatty acids can lead to weight gain and obesity.

On account of the plant-based ingredients in their feed, farmed salmon also provide just as much omega-6 as omega-3. Nevertheless, farmed salmon contain high levels of marine-derived omega-3.

Vitamin D

Vitamin D is a fat-soluble vitamin that is stored in our liver. Fatty fish, fish liver and cod-liver oil are all rich in it.

In Norway, vitamin D is added to some types of milk and dairy products. In summer, our body can make vitamin D in our skin with the help of sunlight. For the rest of the year, our diet determines our vitamin D levels.

The most important role of vitamin D is to maintain a stable level of calcium in our blood. Serious vitamin D deficiency can lead to skeletal disorders, such as rickets in children and osteomalacia in adults. The consequences of mild vitamin D deficiency are less well documented.

The Norwegian population generally has good vitamin D levels, particularly in summer. However, part of the population has low vitamin D levels in winter. Children, pregnant and breastfeeding women and the elderly are most affected. As people with darker skin types produce less vitamin D in their skin, non-Western immigrants are particularly at risk of vitamin D deficiency in Norway.


Selenium is a chemical element that is found in lean and fatty fish, as well as in products made from grains. Elements found in small quantities in living organisms are known as “trace elements”.

Selenium plays an important role in areas such as reproduction and our immune system. It may also play a role in cardiovascular disease, cancer and mental health.

We have 5-15 milligrams of selenium in our body, in our cells and tissues, with most of it being in our liver and kidneys. We consume it through a variety of foods.

Our daily intake is thought to be 70-80 micrograms, but the amount we need has not been ascertained.

Nutrients and unwanted substances interact

When we eat, we don’t eat nutrients or unwanted substances one by one. We eat a combination of them – the whole food product, in other words. When discussing how food products affect our health, we have to take into account all of their contents. Their combined effect may be different from the sum of their individual ones.

Even if a food product contains substances that may be harmful to health, their negative impact may be outweighed by positive ones. The dietary advice given by the health authorities is the result of weighing up positive and negative impacts. The reason they recommend eating a certain amount of seafood per week is that research shows that the positive impacts are bigger than the potential negative ones.

For example, the Food and Agriculture Organization of the United Nations recently confirmed that the protection provided by marine omega-3 fatty acids against cardiovascular disease is much more significant than the risk of developing cancer due to unwanted substances in seafood.

Unwanted substances in seafood

All food contains certain levels of unwanted substances. In the case of farmed fish, these may be substances that are used to make food production more efficient (such as delousing agents), or substances in the environment from either natural or human sources. They include organic pollutants such as dioxins and dioxin-like PCBs, as well as heavy metals like lead and cadmium. Seafood may also contain parasites and bacteria that either affect its quality as a food product or cause illness in humans.

The Institute of Marine Research monitors the levels of unwanted substances in various types of both farmed and wild seafood.(link to article on safe seafood). 

Arsenic is a heavy metal that is found in small quantities all over the Earth’s crust. It is also produced by industrial activities and was previously used in agriculture as a pesticide.

Marine fish contain arsenic in over ten different chemical compounds, the majority of which are organic compounds that are not poisonous.

Inorganic arsenic compounds such as arsenic trioxide are carcinogens, and they also affect our nervous system. The oceans contain organic compounds of arsenic that are soluble in water.

The main compound found in fish and other seafood is arsenobetaine, which is a non-toxic form of arsenic. Humans absorb arsenobetaine, but they excrete it unchanged.

Cadmium is a heavy metal that is found naturally in the environment, including in soil. Cadmium has also been used in a wide range of industrial processes, including in batteries and mining, and to protect steel against rusting. It is transported in both the water and air, and enters the oceans via rivers.

Grain products and vegetables are the most important source of cadmium in Europe. Cadmium isn’t absorbed much by fish, but it can accumulate in crustaceans.

Cadmium, which has a long half-life in humans, can cause cancer. It can also accumulate in our kidneys, leading to kidney failure, as well affecting our ability to reproduce.

Mercury is a heavy metal found in various chemical forms. The most toxic form is organic mercury, also known as methylmercury.

Mercury occurs naturally in the environment from sources such as volcanic eruptions and degassing. Human activities such as mining and industry also lead to mercury emissions.

Methylmercury is passed from the mother to her baby during pregnancy, and large quantities of it can cause deformities in the child. It also affects the mental development of both foetuses and infants, and may reduce learning ability and negatively affect fine motor skills.

Fish and other seafood, and particularly lean fish, is currently the main source of mercury in our diet.

Dioxins and dioxin-like PCBs are organic pollutants that contain chlorine.

These days, most dioxins come from combustion, and of the 210 different dioxin compounds, 17 are particularly poisonous. Polychlorinated biphenyls, or PCBs, are a group of industrial chemicals that were developed in the 1920s. PCBs were used in products like transformer oil, paint and refrigerants, but they were banned in Norway in 1980.

12 of the 209 PCB compounds are referred to as dioxin-like PCBs, because they behave in the same way as dioxins. Dioxins and dioxin-like PCBs are both hard to break down and fat-soluble, which means they accumulate in the food chain and in the bodies of fish, other animals and humans. They are found in fatty fish, meat, dairy products and eggs. In fatty fish they are found in the fillet, whereas in lean fish they are in the liver.

Dioxins and dioxin-like PCBs are carcinogens and during pregnancy they can cause foetal deformities.

Brominated flame retardants are a group of around 70 substances that contain the chemical element bromine. They are used in a variety of products from textiles to electronics to prevent them from catching fire.

These chemicals reduce the risk of fire by raising the ignition temperature of materials. Brominated flame retardants are particularly widely used in electrical and electronic equipment, paint, car parts, synthetic textiles, furniture, construction materials and packaging.

Many of them are considered persistent organic pollutants, and most of them are now illegal to use. We are exposed to these chemicals through the air and our food, and in the case of seafood they are found in fatty fish.

Ethoxyquin (EQ) is a synthetic antioxidant that is often added to fish meal to prevent it from exploding during transport by sea and storage.

During 2020, ethoxyquin as an additive in feed was phased out, because it was no longer approved for use in the EU and Norway. It is not permitted to use ethoxyquin as an additive in food

Before this, feed containing fish meal therefore also could contain ethoxyquin. Ethoxyquin is transferred from the feed to the fish fillet, but there it is quickly transformed into other compounds.

With the help of new analytical tools, researchers have ascertained which compounds ethoxyquin is transformed into in the fish fillet. They found many different compounds, with the most common one being ethoxyquin dimer (EQDM). Ethoxyquin dimer has a long half-life and takes a long time to disappear from salmon fillets.

There is no evidence of exposure to ethoxyquin causing any harm to humans, but in experiments, mice given high doses of it showed signs of oxidative stress and of disruptions to their metabolism of fat that could be a precursor to fatty liver.

Butylated hydroxyanisole (BHA) is a synthetic antioxidant that is mainly added to fish oil to prevent the fat from going rancid.

Fish oil is used as an ingredient in fish feed, and some BHA is therefore present in that fish feed. BHA is less widely used than the other synthetic antioxidants. It is used in some food products such as cake mixes, snacks and powdered milk. In seafood it is found at very low levels in farmed salmon that has been given feed containing BHA.

There is no evidence of exposure to BHA causing any harm to humans, but experiments on rats have shown that it can be carcinogenic if taken in large doses.

Butylated hydroxytoluene (BHT) is a synthetic antioxidant that is mainly added to fish oil to prevent the fat from going rancid.

Fish oil is used as an ingredient in fish feed, and some BHT is therefore present in that fish feed. BHT is found in many food products such as sauces, chewing gum and food oils, but in seafood it is only found in farmed fish that has been given feed containing BHT. This is the synthetic antioxidant most commonly found in fillets from farmed salmon.

There is no evidence of exposure to BHT causing any harm to humans, but experiments on rats have shown that it can be carcinogenic if taken in large doses.

The body needs iodine in order to produce the thyroid hormones T3 and T4. These hormones are produced in the thyroid gland and regulate our metabolism throughout our life.

Iodine plays an important role in regulating the metabolism of adults and is important to the growth and development of children. Norwegian studies suggest that mild to moderate iodine deficiency in mothers may be associated with impaired cognitive development in their children.

Lean fish is the food in the Norwegian diet with the highest iodine content, but dairy products are nevertheless the population’s most important source of iodine.

Read more about why iodine is particularly important to the health of pregnant women and children (LINK).