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Fish oil does not increase the risk of bleeding

Fish oil does not increase the risk of bleedingFor decades, medical science has claimed that fish oil increases the risk of bleeding and has therefore warned against taking fish oil supplements prior to surgery. A large, systematic review of studies that is now published in the Danish Medical Journal shows that fish oil supplements do prevent blood platelets from aggregating, but this biochemical effect is not associated with increased bleeding risk in connection with surgery. It is therefore safe to continue taking supplements – and eating oily fish.

Because of fish oil’s blood-thinning effect, health authorities normally advise people to discontinue their use of fish oil supplements no later than one week before planned surgery and to wait until a week after surgery before taking them again.
It now appears that these guidelines are misleading. According to a new meta-analysis conducted by researchers from Aarhus University in Denmark, there is no increased bleeding risk during or after surgery if people take fish oil supplements.
The meta-analysis is based on data from 32 publications with healthy people and 20 publications with people scheduled to undergo surgery. Most publications are based on randomized, placebo-controlled studies. It turned out that fish oil generally reduces blood platelet aggregation and lowers the risk of blood clots in healthy individuals. However, fish oil does not increase bleeding time or the need for blood transfusions during or after surgery.
Besides, it seems illogical that health authorities only warn against fish oil supplements and not against consumption of oily fish, considering that a piece of salmon contains as much omega-3 as 3-4 standard fish oil capsules. Actually, where does our knowledge about fish oil and its health benefits come from, and why are health authorities giving us misleading information?

Groundbreaking Danish research started the whole thing

In the 1970s, a Danish professor named Jørn Dyerberg went with a team of researchers to Greenland to study the diet and health of the Inuit population. Although scientists at that time warned against consuming animal fat, Dyerberg and his team of scientists were the first to show that there was a very low rate of cardiovascular disease among the Inuit people, despite their high intake of meat. The scientists ascribed this to the consumption of fish, seal, and other types of seafood with large quantities of long-chained omega-3 fatty acids (EPA and DHA). Ever since, researchers been looking into the health benefits of fish oil, namely their positive influence on the cardiovascular system, their anti-inflammatory properties etc. Today, fish oil supplements are widely recommended.

Blood platelets, blood clots, and omega-3

Dyerberg and his team of scientists also observed that the Inuit population of Greenland had increased bleeding time compared with the Danish population. It goes without saying that it is vital for blood to be able to coagulate in case a blood vessel is ruptured. The blood platelets are like a circulating “repair kit” and work by gluing together the ruptured vessel and sealing it off. On the other hand, blood platelets are also able to aggregate and form undesirable blood clots in cases where an arterial wall is damaged by atherosclerotic plaque, or if the blood is unable to flow freely. Dyerberg and his scientists actually observed that the blood platelets in the Inuit people contained a lot more omega-3, and they therefore assumed that their diet with all the different omega-3 sources was what explained their lower rate of cardiovascular disease. Ever since, scientists have discussed fish oil and its influence on blood coagulation.

It is time to stop all the warnings

Harry Rice, PhD, a researcher and the vice president of Global Organization for EPA and DHDA, welcomes the new publication from Danish Medical Journal and praises the authors’ heroic review of omega-3 fatty acids and bleeding risk. As Rice sees it, it is hardly a surprise that the researchers’ thorough review of studies confirms earlier reports where no link has been found between fish oil and increased risk of bleeding. He also stresses that two of the included studies show a reduced need for red blood cell transfusion in surgery patients who take fish oil supplements. Therefore, Rice finds that it is time to stop all the warning against taking fish oil in connection with surgery.


Katrine Munk Begstrup, Andreas Engel Krag & Anne Mette Hvas. No Impact of fish oil supplement on bleeding risk; a systematic review. Danish Medical Journal. 2017

Stephen Daniels. Fish oils & bleeding risk: Extensive review supports safety of supplements. NUTRA 2017

Jerk W. Langer. Politikens Store Lægebog. Politikens Forlag 2007

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