Answer:

Yes, very high doses of fish oil may suppress the immune system as well as have blood-thinning effects.

In people taking highly concentrated prescription fish oil, elevations in "bad" LDL cholesterol and certain liver enzymes, and an increase in episodes of atrial fibrillation or atrial flutter in people who already have this heart rhythm disorder, have been reported.

Be aware that cod and other fish liver oils can be high in vitamins A and D, which can be toxic in high doses. Too much vitamin A, for example, can cause liver damage. Too much vitamin D can cause hypercalcemia (too much calcium in the blood), resulting in symptoms such as constipation, confusion, weakness and loss of appetite. (See the Concerns and Cautions sections of the Vitamin A Supplements Review and the Vitamin D Supplements Review for more details and upper intake limits for these vitamins).

While fish oil is not believed to adversely affect blood sugar levels in people with diabetes, one study found that taking a large amount of krill oil which contained relatively modest amounts of EPA + DHA (230 mg and 154 mg, respectively) was shown to significantly reduce insulin sensitivity in overweight, middle-aged men, which could potentially increase the risk of the risk of diabetes and cardiovascular disease.

Also be aware of potential drug interactions with fish oil, as discussed in the Concerns and Cautions section of the Fish Oil and Omega-3 Fatty Acids Supplements Review.

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9 Comments

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tom18614
November 9, 2019

I just read dha is linked with a big correlation with Prostata cancer! What thinking now?

ConsumerLab.com
November 15, 2019

Hi Tom - Thank you for mentioning this. You can find information about omega-3s, fish oil and prostate cancer in the "Cancer" section of the Fish Oil Review: https://www.consumerlab.com/reviews/fish-oil-supplements-review/omega3/#prostate.

Alan18586
November 1, 2019

To the moderators: Just food for thought. Recently had a cholecystectomy, and was alarmed at my post-op lipid profile. There is good evidence on PubMed that says a rise in hepatic triglycerides and a commensurate rise in VLDL are the norm, following this procedure, so enterohepatic metabolism of cholesterol will most definitely be altered. My LDL, however, was well within the normal range, which was also commensurate with PubMed data. I only wish my GI doc had informed me of these imminent changes BEFORE the procedure.

Richard16928
July 1, 2018

I'm stunned that with all the expertise your suppose to have that you are absolutely clueless about prescription Vascepa and how it differs from ALL other prescription and OTC fish oils..there is nothing like it please check it out and do your DD

ConsumerLab.com
July 2, 2018

Hi Richard - Actually, we are well aware of VASCEPA and it is mentioned several times in our Fish Oil report, including a discussion of its effects and side effects relative to other fish oils. See the paragraph here: https://www.consumerlab.com/reviews/fish-oil-supplements-review/omega3/#vascepa

Robin16924
July 1, 2018

Please reconsider Krill Oil as a supplement. The impact on an already deminishing population of Krill affects Endangered Species of Whales Penguins . Thank you ConsumerLab, we love what you do. Perhaps include a link to the environmental dangers of Commercial fishing of Krill that many Scientists and groups are fighting against. I won't name names but some stores won't carry Krill oil and others pushing it.

ConsumerLab.com
July 2, 2018

Thank you Robin. This is a valid concern that we discuss in the Fish Oil and Omega-3 Fatty Acids Review, here: https://www.consumerlab.com/reviews/fish-oil-supplements-review/omega3/#harvesting

Peggy16855
May 21, 2018

So how much is too much regular (not prescription) fish oil caps in mg?

ConsumerLab.com
May 21, 2018

Hi Peggy - If you click on the first link in the answer, it will take you to the section of the Fish Oil Review that provides this information ( https://www.consumerlab.com/reviews/fish-oil-supplements-review/omega3/#immune).

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