Evidence for Nutrition Recommendations: DHA & Prostate Cancer

A reader sent me a link to this study, DHA inhibits differentiation of prostate fibroblasts into myofibroblasts and tumorigenesis, and asked me if it changed my recommendations that vegans (under age 60) don’t need to supplement with DHA every day.

The study is in vitro and animal research, and indicates that DHA can prevent prostate cancer growth. I told him that it did not change my recommendations and he asked me to make a blog post to explain why.

Creating nutrition recommendations is not something that should be taken lightly. The United States government calls upon the National Academy of Sciences to make nutrition recommendations for the nation. This is done through the Institute of Medicine’s Food and Nutrition Board and the recommendations are referred to as the Dietary Reference Intakes (DRI).

All known essential nutrients are given a DRI. In most cases, these are based on a large body of research and arrived at by a panel of experts in the area. The research they have reviewed for most nutrients has been based on acute symptoms of deficiency and toxicity; they are rarely based on long-term, chronic disease prevention. This may be changing as more research becomes available and acute deficiencies are no longer the problem they once were.

So, with that background, a very good reason would be needed for me to overrule the Institute of Medicine and set my own “DRI.” But because the DRI are not set with vegans in mind, we have to fill in the gaps and most of my recommendations are to get vegans in compliance with the spirit of the DRI.

The study on DHA and prostate cancer, mentioned above, is only a test-tube and animal study. The results may or may not translate for humans, and even if they do, there is no way to know how much humans need to take to achieve such results or if there are negative side effects from taking whatever level of DHA we might determine is appropriate. The Food and Nutrition Board would not make recommendations based on one in vitro or animal study. There are many studies looking at DHA intake and levels in humans and associated diseases and these studies are fraught with confounding variables with no clear answer as to how much DHA humans should be taking on a regular basis to prevent overall chronic disease.

Some vegan RDs do not think it’s necessary to recommend DHA for vegans; I choose to do so, but err on the conservative side. The Food and Nutrition Board has not created a DRI for DHA, but given that studies have shown that vegans have much lower levels of DHA in the blood than your average person, I recommend DHA to make sure that we are not at a disadvantage compared to non-vegans. If you want to see the reasoning behind my DHA recommendations, you can read it in Omega-3 Fatty Acid Recommendations for Vegetarian.

For more information on the types of studies that provide more evidence for nutrition recommendations than others, please see my article Basics of Nutrition Research.

In conclusion, I try not to supersede the Food and Nutrition Board in formulating nutrition recommendations and I do not change recommendations based on in vitro or animal studies.

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15 Responses to “Evidence for Nutrition Recommendations: DHA & Prostate Cancer”

  1. Bertrand Russell Says:

    I think your previous link is also relevant here:
    http://www.motherjones.com/kevin-drum/2013/01/sad-story-fish-oil-and-small-sample-sizes

  2. Dan Says:

    Jack, I was wondering if you could explain the rationale behind your recommendation to dose DHA q2d rather than qOD (at least, for those under the age of 60). Appreciate your thoughts on this.

    Dan

  3. Jack Norris RD Says:

    Dan,

    I don’t have any good mathematical analysis for these recommendations other than to say that based on the entirety of the research, I think this is an amount that will provide insurance for vegans in case DHA is, indeed, necessary for cognitive function. If you look at Table 9 on this page http://veganhealth.org/articles/omega3 you will see that 1,600 mg provided more than enough to raise blood levels. And, that’s a lot more than I recommend. Hopefully, there will be more evidence in years to come.

  4. Dan Says:

    Heh Jack,
    The papers I saw in medline all used daily dosing in veg*ns. I wonder if you know what the half-life of DHA is? Likely higher in the tissues (ie as incorporated phospholipids in cell membranes) than in the blood, where we can measure it.
    Reason I ask is that vegan DHA is so expensive. If every-other-day dosing is a reasonable extrapolation of the data, it would be half the price!

  5. Jack Norris RD Says:

    > The papers I saw in medline all used daily dosing in veg*ns.

    What papers – the ones I mention in my article that use about 1,600 mg? If you know of others, I’d like to see the citations so I can check them out.

    No, I have no idea what the half-life of DHA might be.

  6. Dan Says:

    If you pop the following search string into Pubmed, n=22 articles come up, some of them quite interesting –

    (“Docosahexaenoic Acids”[Mesh] AND “Diet, Vegetarian”[Mesh])

  7. Dan Says:

    Jack …for example….

    Sanders (PMID: 19500961) — “We have conducted a placebo-controlled randomized trial in vegan subjects with serum vitamin B12 concentrations >200 ng/L, which has so far been published only as an abstract. In this study, 200 mg DHA/d taken for 3 months [27] increased the proportion of DHA in plasma by 50% (Fig. 1).”

    Geppert (PMID: 16296399) — “Healthy vegetarians (87 f, 17 m) consumed daily a microalgae oil from Ulkenia sp. (0.94 g DHA/d) or olive oil (placebo) for 8 wk … We conclude that an 8-wk supplementation with 0.94 g DHA/d from microalgae oil achieves a beneficial omega-3 index of > or =8% in most subjects with low basal EPA + DHA status.”

    Wu (PMID: 16278686) — “After a 2-week run-in period with 6 g placebo corn oil, the subjects were subsequently randomized to receive either 6 g corn oil (n=13) or 6 g DHA-rich algae oil (2.14 g of DHA/day) (n=14) for 6 weeks …. DHA supplementation at a dose of 2.14 g/day for 42 days decreases plasma cholesterol but neither does it show beneficial effects on estrogen metabolism, nor does it induce deleterious effects on the observed in vivo antioxidant or oxidative stress marker in postmenopausal vegetarian women.”

    Mezzano et al (PMID: 11108902) — “Ten of fourteen of these vegetarians completed an 8-week supplementation with 700 mg/day of each eicosapentaenoic and docosahexaenoic acids … Increased incorporation of these fatty acids into plasma lipids was observed in all of them, together with a significant reduction in maximum percentage or slope of platelet aggregation with all the agonists tested (ADP, epinephrin, collagen, arachidonic acid).”

    Conquer et al (PMID: 9076673) — “an EPA-free preparation of DHA was given as a daily supplement (1.62 g DHA) over a period of 6 wk. The dietary supplement provided for a marked increase in DHA levels in both serum phospholipid (from 2.1 to 7.1 mol% in vegetarians and 2.2 to 7.6 mol% in omnivores) and platelet phospholipid (from 1.1 to 3.4 mol% in vegetarians and 1.4 to 3.9 mol% in omnivores).”

    Conquer et al (PMID: 9001371) — “Healthy vegetarians (12 male, 12 female) consumed nine capsules daily of either DHA (1.62 g/d) or corn oil for 6 wk. Consumption of DHA capsules increased DHA levels in serum phospholipid by 246% (from 2.4 to 8.3 g/100 g fatty acids) and in platelet phospholipid by 225% (from 1.2 to 3.9 g/100 g fatty acids).”

    Therefore, the doses used in these studies considerably exceed your recommendation of 200-300 mg of DHA every 2-3 days for people under age 60. For example, if someone were to take 200 mg every 3 days, they would be getting about 66 mg/d (0.066 g/d). On what literature did you base your recommendation, and should it be changed to reflect these supplementation trials in vegeterians?

    And these are just the studies in vegetarians. I am sure I could find some in non-vegetarians using similar dosing strategies.

  8. Jack Norris RD Says:

    Thanks, Dan! I will check these out as soon as I can. Glancing over it, I’m familiar with some of the studies, but will look in more detail when I can.

  9. Dan Says:

    I can also provide you with the abstract mentioned above (by email). It was a large (n=76 or 75) randomized placebo-controlled blinded trial of DHA vs placebo in vegetarians, using 200mg/day dosing. And the level did not come up to that see in omnivores, which really makes me question 200mg q2-3d.

  10. Jack Norris RD Says:

    Dan,

    Can you paste it here?

  11. Dan Says:

    I tried to cut-and-paste it and the system rejected it. It was not very long either. I’m not sure why – I got a weird error. However, the abstract is available for free, I will paste the url later – it’s on a different computer.

  12. Dan Says:

    Jack, here is the URL:

    http://journals.cambridge.org/download.php?file=%2FPNS%2FPNS62_1a%2FS0029665103000776a.pdf&code=c4a462d607a0579991f4e05f6aebbcf2

    (see page 42A of the PDF that loads)

    Reference: Z. LLOYD-WRIGHT, R. PRESTON, R. GRAY, T.J.A. KEY and T.A.B. SANDERS. Randomized placebo controlled trial of a daily intake of 200 mg docosahexaenoic acid in vegans. Proc Nutr Soc (2003) 62:42A

    Conclusions: “Plasma DHA concentrations increased by 50%
    on DHA treatment but still did not achieve the concentrations seen in omnivores.”

    Sounds like if the goal is to make vegan DHA levels the same or similar to that of omnivores, it is going to take alot more than 200-300 mg q2-3d. Interesting, because the average intake in omnivores is only about 20 mg/d. This trial is the lowest dose of any of the trials (200 mg/d), still quite a bit above your recommendation (except for your modification of your recommendation in people older than 60).

  13. Dan Says:

    If that URL doesn’t work, try:

    http://journals.cambridge.org/action/displayIssue?decade=2000&jid=PNS&volumeId=62&issueId=1a&iid=815032

    (copy and paste it into a browser)

  14. Jack Norris RD Says:

    Dan,

    I responded to your comments and list of citations here:

    http://jacknorrisrd.com/dha-recommendations-updated-a-bit/

  15. Dan Says:

    Jack,
    Thanks for posting that.
    I agree we still have no clue what DHA does in adults, although it may provide some cardioprotective benefit (as shown in recent and remote dog studies).
    Dan

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