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Omega-3 and fish oil

Omega-3 and fish oilOmega-3 fatty acids belong to a group of polyunsaturated fatty acids. Their "omega-3" name indicates that they have a double bond at the third carbon atom in the middle carbon chain. Omega-3 fatty acids provide energy and constitute an important element in all cell membranes and various biochemical processes. The type known as ALA (alpha-linoleic acid) is essential, as the human body is unable to produce it. We depend on a dietary supply of this fatty acid. By means of enzymes, ALA is converted to EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) and finally into some hormone-like substances named prostaglandins (E3).

The conversion from ALA to EPA and DHA is often limited, perhaps because of lacking enzymes. For that reason it is believed that many people are able to benefit more from EPA and DHA when these fatty acids come directly from the diet (mainly from oily fish) or in the form of supplements (fish oil supplements). Human and animal brains contain large amounts of omega-3 and omega-6 that ensure integrity in the neurological network. DHA (and to a lesser extent EPA) is particularly important for a special type of enzyme activity called NOS (nitric oxide synthase activity) and is highly important for memory and learning.

Omega-3 fatty acids are also part of a biochemical interaction with omega-6 fatty acids where the balance between the involved types of fatty acids is vital. For instance, there is competition between EPA and arachidonic acid (omega-6) and the production of hormone-like prostaglandins that control inflammation and other processes in the body.

Functions and importance for

  • Construction of cell membranes
  • Brain function
  • Nervous system
  • The retina
  • Cardiovascular system and heart function
  • Blood pressure
  • Levels of cholesterol and triglycerides
  • Maintenance of soft and pliable skin and other tissues
  • Immune defence
  • Inflammatory processes
  • Joints
  • Hormone-like substances (prostaglandins)
  • Cramps (including menstrual cramps)
  • Normal brain development in the fetus

Deficiencies and poor utilisation may be caused by

  • Unbalanced diets
  • Deep-frying and frying
  • Hydrogenation (industrial hardening)
  • Oxygen and light
  • Too much omega-6

Medical advantages

  • Promotes neurological development
  • Improves cardiovascular health
  • Reduces the tendency towards blood clots
  • Reduces the tendency towards elevated blood pressure
  • Strengthens the immune system
  • Inhibits inflammation
  • Prevents cramps (including menstrual pain)
  • Good for skin problems
  • Bones (osteoporosis)
  • Possibly diabetes

Neurological diseases

Omega-3 fatty acids have been shown to improve ADHD, schizophrenia, and depression (including postnatal depression)

Inflammation and auto-immune diseases

Many chronic diseases are caused by inflammation. Omega-3 fatty acids have demonstrated a beneficial effect against rheumatoid arthritis and systemic lupus erythematosus (SLE). It is primarily EPA that inhibits inflammation by promoting the so-called type-3 prostaglandins (PGE3)

Menstrual pain

Danish research has shown that two grams of fish oil (with folic acid and vitamin B12) may relieve menstrual pain and discomfort.


Laboratory and animal research has shown that EPA/DHA is able to stop the progression of cancer cells in breast and prostate tissue.


Mainly oily fish (mackerel, salmon, herring, anchovies, and sardines), tuna, seal, whale blubber, octopus oil and krill oil with EPA/DHA. Other sources are flaxseed oil, rapeseed oil, walnuts, kiwi, and cranberries with ALA (and a fair amount of omega-6 fatty acids)

Omega-3 content in grams per 100 grams

Flaxseed oil 54 (ALA)
Cod liver oil 21 (EPA/DHA)
Rapeseed oil 9 (ALA)
Walnuts 7 (ALA)
Wild salmon, mackerel, and herring 3-6 (EPA/DHA)

Please note: The conversion of ALA to EPA/DHA is often quite limited

Recommended daily allowance (RDA)

May vary from country to country.

International experts recommend:

  • 500 mg (EPA/DHA) in order to avoid deficiency
  • 1 gram as preventative support of e.g. the circulatory system
  • 2-4 grams for intensive support of e.g. aching joints

Increased need

  • Unbalanced diets
  • Lack of ability to convert ALA from vegetable sources into EPA and DHA
  • Elevated triglyceride levels
  • Morning stiffness in joints and aching joints
  • Inflammatory conditions

Also see "Medical advantages" and the following sections

Overdosing - side effects

  • Typically occurs when fish oil supplements are taken on an empty stomach
  • Fish-like regurgitations ("fish burps")
  • Flatulence and transient loose stools

Especially with higher dosages:

  • Increased tendency towards infection (rare)
  • Increased tendency towards bleeding (not commonly seen)
  • Slightly increased levels of LDL cholesterol in diabetics (rare)

Imbalance between omega-3 and omega-6 levels

Farmed fish, slaughter cattle, chickens, and dairy cattle get far more omega-6 in their feed today. Consequently, fish, meat, eggs, and dairy products often contain less omega-3 than in old days. The combined effect of animal feed, reduced fish intake among humans, consumption of ready meals, and margarine is that most of us get too much omega-6 and too little omega-3. Modern Western diets typically contain omega-6 and omega-3 in a 10:1 ratio (in some cases it can go up to a 30:1 ratio). The optimal ratio is believed to be 4:1 or maybe even less. This imbalance in our fatty acid consumption is thought to be a contributing factor to many of the so-called lifestyle diseases.


Omega-3 fatty acids are important for normal fetal development of the brain and vision, among other things. They also hold the potential to prevent postnatal depression. Pregnant women are advised to consume more fish of different types. However, they should not eat more than 100 grams per week of the large predatory fish, as they tend to contain more mercury and other heavy metals plus organochlorine compounds. Fish oil supplements are particularly well suited as an alternative during pregnancy.


Rancid fatty acids are bad for your health and for that reason the fish oil in supplements should always be stable. The peroxide value expresses the level of rancidity of the oil. The industrial threshold value is below 5 mEq/kg. Most fish oil supplements on the Danish market are below that level. Furthermore, fish oil for human consumption have undergone a screening and cleansing process that removes undesirable substances such as mercury, dioxins, and iron. The way the supplements comply with the upper safe intake levels (threshold levels) for environmental toxins that have been established by the health authorities

Some fish oils are literally odourless while others have a natural taste of fish oil.

Important information about effect

The effect of omega-3 fatty acids accumulates over a certain amount of time until it reaches a steady state. An effect can still be registered for 4-8 (in some cases as much as 10) weeks after discontinuation. As a result of this, the recurrence of health problems may not occur until several weeks after a person discontinues his or her use of fish oil supplements.

Interactions and medicine

There is a theoretical risk that omega-3 fatty acids can interact with blood thinners and acetylsalicylic acid. This interaction has not yet been verified in clinical studies and the implications can therefore not be accounted for at this stage.