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BY Anne-Marie Chalmers, MD Mar 6, 2017

Rancid Fish Oil Is Likely a Health Hazard, New Studies Show

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The effectiveness of omega-3 supplements has been the subject of controversy for some years now. How good for us are they really? It seems that every other week, there’s a new study showing the benefits for omega-3 supplements for brain health, dry eyes or children with allergy issues. And then as soon as we feel comfortable popping those fish oil capsules, another study comes along showing ‘no benefit’ for heart health or even negative effects.

So what exactly is going on? And why are we getting such different results?

Often, news outlets will comment on the different dosages used, poor study designs or increased use of medication to explain away the confusion. And the omega-3 industry might counter by saying the media sensationalized the science.

But there is another factor that scientists are starting to raise, and that is the rancidity level of the oil. Recently, a new review and a study on Alzheimer’s disease came out. These papers add to the body of scientific literature showing that rancid fish oil could explain why some omega-3 supplement studies find positive effects and others do not. Furthermore, these studies build a strong case for why rancid omega-3 supplements could be a serious health concern.

What the Studies Say

Bo and I have written extensively about the importance of getting a fresh fish oil since 2012. We’ve covered everything from how to assess whether your omega-3 supplement is rancid, to documenting the rampant rancidity issues within the fish oil industry, to more technical pieces on peroxide and anisidine values (those are two important freshness measurements). For anybody interested in learning more about fish oil freshness, I recommend clicking on those links.

For this blog though, we’re going to jump into discussing the newest review, courtesy of W. Wang et al from the University of Massachusetts, Amherst. This is not the first review to discuss rancidity. A piece by New Zealand researcher, Benjamin B. Albert, published a comprehensive article on the topic in 2013.

Indeed, most of Wang’s conclusions are not new. But Wang puts forth more up-to-date information that discuss not only the animal studies done on rancid omega-3 supplements, but also some of the trials done on people. At the end of the article, the review states conclusively that the byproducts created when the omega-3 fatty acid oxidizes (or turns rancid) have “a mutagenic and pro-inflammatory” effect, and could be linked with increased cancer risks.

Now if Wang’s review sounds ominous, consider this study that was published in 2016. In it, the researchers looked at the relationship between omega-3 fatty acids and Alzheimer’s disease. Numerous past studies showed that getting enough omega-3, particularly the DHA variety, could reduce the risk of Alzheimer’s disease. However, looking at the postmortem brains of people with Alzheimer’s disease, the researchers also found elevated levels of lipid peroxidation (i.e. those byproducts created when the omega-3 fatty acid oxidizes).

The researchers designed their study to investigate whether oxidized omega-3 fatty acids were just a symptom of Alzheimer’s disease, or if lipid peroxidation could be contributing to the problem. They discovered that when the DHA molecule oxidized, it reverted the molecule’s protective benefits for the brain. They also found that oxidized DHA significantly increased Aβ production, which is widely believed to be a driving cause of Alzheimer’s disease.

Should We Take Omega-3 Supplements?

These findings are shocking. And they are especially shocking considering that studies around the world have found over 80% of the omega-3 supplements on the market exceed relatively lax industry freshness standards. This includes omega-3 formulations for pregnant women and infants.

But the right conclusion is not to give up on omega-3 altogether. Omega-3 fatty acids are vital for our health, making up an important part of every cell in the body. Most of us, especially in the United States, do not get enough omega-3. And as both Albert and Wang suggest, omega-3 supplements have the potential do a lot of good for preventing and treating diseases, including certain types of cancer and cardiovascular disease.

Furthermore, truly fresh omega-3 oil exists, and it is available. Our Omega Cure®, for instance, has a peroxide value between 0.1 – 0.3 at the time of bottling, matching the quality of fresh fish. And since we ship Omega Cure directly to the consumer only a few weeks thereafter and it is always kept cold, it’s peroxide value is at least 50 times fresher than your typical fish oil capsule.

How Omega Cure Compares: Peroxide Oxidation Level Chart
Looking at an omega-3 oil’s peroxide value is one of the primary ways to assess its freshness level.

Because most consumers don’t realize that their oil is rancid and because the technology and equipment needed to create fresh fish oil is expensive, most manufacturers don’t bother with it. But if the demand, awareness and regulation was there, I am sure this would change.

In the meantime, avoiding fish oil is not a great solution. With any kind of oil, be it flaxseed, krill or olive oil, you run into rancidity issues. Even eating fish does not mean you are immune from the effects of lipid peroxidation. Depending on how your fish was killed, stored, and finally cooked can all impact the quality of the omega-3 fatty acids. Instead, Bo and I believe that combating rancidity has to begin with awareness and education.

In Conclusion

Freshness matters. As consumers, freshness is something we have to be aware of, and we need to seek out quality oils. For fish oil, consumers need to demand higher freshness standards. Ask to see your omega-3 supplement’s peroxide and anisidine values. Be attentive to how it is stored. And at the very minimum, use the taste and smell test to assess the quality of your oil.

Following those principles, you can make sure you are getting a fresh oil and experiencing the full benefits of omega-3 fatty acids.

fresh full spectrum fish oil dose omega 3 innovations


1. W. Wang, et al., Chemistry and Biology of -3 PUFA Peroxidation-Derived Compounds, Prostaglandins Other Lipid Mediat (2016). http://dx.doi.org/10.1016/j.prostaglandins.2016.12.004

2. Benjamin B. Albert, David Cameron-Smith, Paul L. Hofman, and Wayne S. Cutfield. Oxidation of Marine Omega-3 Supplements and Human Health. BioMed Research International, vol. 2013, Article ID 464921, 8 pages, 2013. doi:10.1155/2013/464921

3. Grimm MO et al. Oxidized Docosahexaenoic Acid Species and Lipid Peroxidation Products Increase Amyloidogenic Amyloid Precursor Protein Processing. Neurodegenerative Diseases. 2016;16(1-2):44-54. doi: 10.1159/000440839

4. Murphy MP, LeVine H. Alzheimer’s Disease and the β-Amyloid Peptide. Journal of Alzheimer’s Disease : JAD. 2010;19(1):311. doi:10.3233/JAD-2010-1221.

5. Guilia Secci, Guiliana Parisi. From Farm to Fork: Lipid Oxidation in Fish Products. Italian Journal of Animal Issues, vol. 15: 124 – 136, 2016. http://dx.doi.org/10.1080/1828051X.2015.1128687

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2 thoughts on “Rancid Fish Oil Is Likely a Health Hazard, New Studies Show”

  1. Delaney says:

    I bought 2 bottles of the fish oil yesterday and unfortunately both thawed due to freezer door being left open. Can I refreeze? How long does a bottle last if thawed and in fridge? Thanks.

    1. Omega3 Innovations says:

      Hi Delaney! That’s not a problem, you can absolutely refreeze Omega Cure, it won’t hurt the oil. Unopened and stored in the refrigerator, the bottle will last nicely for up to 3 – 4 months. Once you open the bottle, however, you do need to use it up within 5 – 6 weeks since the oil will start to oxidize with exposure to oxygen.

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