Does DHA Cause Cancer?

fish oilIn the last article we discussed a bit about the cardiovascular benefits of DHA and fish oil. Today we look at a drawback….if you believe the media hype. That is the cancer causing effect of consuming DHA. Does DHA cause cancer?

No it doesn’t, at least not in this man’s opinion!

A study came out a few months back that associated higher blood levels of DHA with prostate cancer in men. Headlines made the news and I received some alerts from various organizations about how DHA is your prostate’s worst enemy blah blah blah. You get the picture. I really didn’t give it much thought because usually when the media grabs onto something like this and blow it out of proportion like they did, it usually isn’t what they’re reporting on. So lets look at a few things.

First this study was a case cohort study meaning that the researchers took a picture, so to speak, of men and their lab results measuring various things to see if they could come up with any associations.1 What they found were men that had the highest levels (relatively speaking compared to others in the study) of DHA also had significant associations of cancer in the prostate. It’s almost analogous to me taking a picture of you on a cloudy day and if you happen to have gout, ipso facto the cloudy day must be the cause of your gout. You can see the problem with this logic. There was no time component to this study and since it wasn’t a prospective randomized trial we can’t assign blame to DHA or anything else for that matter, we can only say, “In this snapshot of men we took, the ones that had higher levels of DHA also had more prostate cancer”. It is not causation.

Correlation does not equal causation. You could say that having prostate cancer increases your risk for having high DHA levels based on this evidence, as if having DHA in your blood is bad. An earlier study with the same group found no correlation between omega-3’s or DHA and cancer. 2 One commenter posited that it may be possible that by simply having cancer one might turn to fish oil for an anti-cancer effect they may have heard of and this would explain the difference. But the real reason that these men had high DHA and cancer at the same time…sorry folks, we just don’t know.

It’s important to remember that these studies aren’t worthless. They give us information on which we can ask some good questions. Those questions form a basis for more prospective trials that really look at causation rather than correlation and that’s important. But the next time you see anything in the media relating to health (or probably anything else for that matter) and they are blowing it up, it’s likely because it was small to begin with and the news has to make things big in order to make money.

Some other studies of interest have been done that are favorable to DHA. One was done in mice where two diets were fed of n-6 and n-3 fatty acids to look at changes in colon carcinoma and found that DHA inhibits around 81% growth and 41% cell proliferation in a strain of that cancer.3

Another study found that DHA enhanced apoptosis with 5-fluorouracil (a cancer drug) and decreased the concentration required of the drug to treat the cells.4 This is really important seeing as how if we can use lower amounts of cancer drugs we could significantly lower the side effects associated with them.

Another in-vitro study found that DHA helps to down regulate Her2/neu in breast cancer cells and like the study above, enhanced the effects of the antineoplastic drugs against those lines.5 Of course we need to test these in vivo situations to see if they pan out in a fully functioning human, but the results are promising. It is results like these, if they get into the public’s ear, that could explain why levels might be high with a person who has prostate cancer, because they want it to get treated and take supplements. But again we don’t know for sure.

An in vivo study was done with paclitaxel (cancer drug) and DHA in combo for later stage lung cancer patients. They didn’t look at cancer therapy vs cancer therapy + DHA so it’s hard to know if there was any real benefit. The response rate of 4.5% didn’t meet the requirements of 10% by the researchers and they rejected the idea of using DHA as a useful therapy in non small cell lung cancer.6 I’m not sure why they set up the study the way they did and by their own admission they had small numbers, but at least for non small cell lung cancer DHA might not be what the doctor ordered. I think it important to note that these were later stages of cancer and that might have been enough to tip the scales in the favor of the cancer, but this is speculation.

There is no proof in my mind that DHA causes cancer. In fact it may be useful in treating cancer. So if you have cancer, taking that fish oil is likely doing nothing to harm you further and may be helping you. And remember, anytime you see anything big in the news relating to something big, in this case cancer, take it with a grain of salt and do some research. News companies are trying to make money, not necessarily take care of your health.


Disclaimer: All info on this website is for education purposes only. Any dietary or lifestyle changes that readers want to make should be done with the guidance of a competent medical practitioner. The author assumes no responsibility nor liability  for the use or dissemination of this information. Anyone who chooses to apply this information for their own personal use does so at their own risk.

1.Brasky, Theodore M., et al. “Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial.” Journal of the National Cancer Institute 105.15 (2013): 1132-1141.

2.Kristal, Alan R., et al. “Diet, supplement use, and prostate cancer risk: results from the prostate cancer prevention trial.” American journal of epidemiology 172.5 (2010): 566-577.

3.Kato, Taeko, Nicole Kolenic, and Ronald S. Pardini. “Docosahexaenoic acid (DHA), a primary tumor suppressive omega-3 fatty acid, inhibits growth of colorectal cancer independent of p53 mutational status.” HNUC 58.2 (2007): 178-187.

4.Calviello, Gabriella, et al. “Docosahexaenoic acid enhances the susceptibility of human colorectal cancer cells to 5-fluorouracil.” Cancer chemotherapy and pharmacology 55.1 (2005): 12-20.

5.Menendez, J. A., R. Lupu, and R. Colomer. “Exogenous supplementation with ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA; 22: 6n-3) synergistically enhances taxane cytotoxicity and downregulates Her-2/neu (c-erbB-2) oncogene expression in human breast cancer cells.” European journal of cancer prevention 14.3 (2005): 263-270.

6.Payne, Miranda, et al. “DHA-paclitaxel (Taxoprexin) as first-line treatment in patients with stage IIIB or IV non-small cell lung cancer: report of a phase II open-label multicenter trial.” Journal of Thoracic Oncology 1.9 (2006): 984-990.


One thought on “Does DHA Cause Cancer?

  1. Pingback: Busting Up Arthritis with Fish Oil | The Pharmacy Brute

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