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Do Omega-3s Cause Cancer in Women?

Mass media was waiting for something like this... so hopefully readers of this blog will be able to have an educated opinion when the topic arises with friends and family.

A new study on omega-3 fatty acids suggests it can significantly increase the risk of cancer in women--but is this really true? I don't think so. When you look at the totality of evidence, it would suggest the opposite, but let's look specifically at the study at hand.

Called the Supplementation with Folate, Vitamins B6 and B12 and/or Omega-3 Fatty Acids (SU.FOL.OM3) trial, the study was designed to investigate prevention of secondary cardiovascular disease. In the study, 45-80 year olds were randomized in a 2x2 factorial design to one of four study arms:
  1. B vitamins: 5-methlytetrahyrdofolate (the active folic acid metabolite) 560 mcg, 3 mg vitamin B6, and 20 mcg vitamin B12 
  2. Omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) 600 mg
  3. B vitamins AND omega-3 fatty acids, or
  4. Placebo
The main results showed that treatment with vitamin B or omega-3 fatty acids had no effect of major cardiovascular events. However, given the availability of the data, the researchers then examined the benefit of these supplements on cancer risk.

In an age- and sex-adjusted multivariable model, there was no effect of the B vitamins or omega-3s on cancer incidence and cancer mortality. The investigators did, however, observe a statistically significant interaction by sex, with women taking omega-3 fatty acids at an increased for cancer and cancer mortality--in fact, a threefold greater risk of developing cancer, and a fivefold increased risk of dying from cancer. Ouch...that's kinda scary.

However, even the researchers caution against reading too much into the increased cancer risk in women taking the omega-3 fatty acids, given that there were only 29 cancer cases in females, compared with the 145 cases that occurred in males, so the findings are only preliminary and hypothesis-generating for future studies.

In fact, their own statistical analysis shows how weak the data was, with very large ranges in what's called the "Confidence Interval" (meaning, statistically, they are not confident in the accuracy of their data).

Also consider that cancers are typically slow growing. It usually takes decades from the initiation of cancer cells to clinical manifestations. Five years is not nearly enough time to determine the effect of supplementation on cancer risk. In fact, it's almost a certainty that those who were diagnosed with cancer during the study period already had cancer before the study--it just hadn't been diagnosed yet.

Lastly, we have no further information on the type of omega-3s they were taking. How pure were they (we know common contaminants in fish oils are carcinogenic)? What form where the fatty acids in (the natural triglyceride form or the more common synthetic ethyl esters)?

For me, there is just too many unanswered questions and too many holes in this study to give it much weight. Again, you can't base conclusions on a particular supplement from one study. Some of you may have heard me say, "nothing is 100% good, and nothing is 100% bad." Every compound studied, whether a synthetic drug or natural substance will have positive and negative studies. You really must look at the totality of evidence to determine the bigger picture.

Source: B Vitamin and/or ω-3 Fatty Acid Supplementation and Cancer: Ancillary Findings From the Supplementation With Folate, Vitamins B6 and B12, and/or Omega-3 Fatty Acids (SU.FOL.OM3) Randomized Trial

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  1. their ages might also be a factor here... 45-80? i think its probably really common that by 80 years old you will be diagnosed with some sort of cancer!

  2. Thanks for covering this. I think it's really important to have a second opinion as yours since I do believe many of these researchers are just out for sensational headlines and a chance in the spotlight (like when they only looked at the cancer link when their results for cardiovascular health came back blank).

  3. I must have missed this post when you published it. This is interesting, but you're last sentence is right. We need to consider the totality of the evidence. Giving any weight to this study would be like giving weight to a new study (hypothetically) that shows smoking cigarettes are healthy in a sea of other studies that prove how toxic it is.


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