Yet Another Negative Trial with Vitamins in Prostate Cancer: Vitamins C and E.

15 12 2008

Within a week after the large SELECT (Selenium and Vitamin E Cancer Prevention) Trial was halted due to disappointing results (see previous posts: [1] and [2]), the negative results of yet another large vitamin trial were announced [7].
Again, no benefits were found from either vitamin C or E when it came to preventing prostate ànd other cancers.
Both trials are now prepublished in JAMA. The full text articles and the accompanying editorial are freely available [3, 4, 5].

In The Physicians’ Health Study II Randomized Controlled Trial (PHS II), researchers tested the impact of regular vitamin E and C supplements on cancer rates among 14,641 male physicians over 50: 7641 men from the PHS I study and 7000 new physicians.

The man were randomly assigned to receive vitamin E, vitamin C, or a placebo. Besides vitamin C or E, beta carotene and/or multivitamins were also tested, but beta carotene was terminated on schedule in 2003 and the multivitamin component is continuing at the recommendation of the data and safety monitoring committee.

Similar to the SELECT trial this RCT had a factorial (2×2) design with respect to the vitamins E and C [1]: randomization yielded 4 nearly equal-sized groups receiving:

  • 400-IU synthetic {alpha}-tocopherol (vitamin E), every other day and placebo (similar to the SELECT trial)
  • 500-mg synthetic ascorbic acid (vitamin C), daily and placebo
  • both active agents
  • both placebos.

Over 8 years, taking vitamin E had no impact at all on rates of either prostate cancer (the primary outcome for vitamin E), or cancer in general. Vitamin C had no significant effect on total cancer (primary outcome for vitamin C) and prostate cancer. Neither was there an effect of vitamin E and/or C on other site-specific cancers.

How can the negative results be explained in the light of the positive results of earlier trials?

  • The conditions may differ from the positive trials:
    • The earlier positive trials had less methodological rigor. These were either observational studies or prostate cancer was not their primary outcome (and may therefore be due to chance). (See previous post The best study design for dummies).
    • Clinical data suggest that the positive effect of vitamin E observed in earlier trials was limited to smokers and/or people with low basal levels of vitamin E, whereas animal models suggest that vitamin E is efficacious against high fat-promoted prostate cancer growth (20), but lacks chemopreventive effects (i.e. see [1,4] and references in [5], a preclinical study we published in 2006).
      Indeed, there were very low levels of smoking in the PHS II study and the effect of the vitamins was mainly assessed on induction not on progression of prostate cancer.
    • Eight times higher vitamin E doses (400IE) have been used than in the ATCB study showing a benefit for vitamin E in decreasing prostate cancer risk! [1,4]
  • Other forms of vitamin E and selenium have been proposed to be more effective.
  • As Gann noted in the JAMA-editorial, the men in both recent studies were highly motivated and had good access to care. In SELECT, the majority of men were tested for PSA each year. Probably because of this intense surveillance, the mean PSA at diagnosis was low and prostate cancers were detected in an early, curable stage. Strikingly, there was only 1 death from prostate cancer in SELECT, whereas appr. 75-100 deaths were expected. There also were indications of a deficit in advanced prostate cancer in PHS II, although a much smaller one.
    In other words (Gann):
    “how can an agent be shown to prevent serious, clinically significant prostate cancers when PSA testing may be rapidly removing those cancers from the population at risk before they progress?”
  • Similarly, in the SELECT trial there was no constraint on the use of other multivitamins and both studies put no restriction on the diet. Indeed the group of physicians who participated in the PHS II trial were healthier overall and ate a more nutritious diet. Therefore Dr Shao wondered
    “Do we really have a placebo group – people with zero exposure? None of these physicians had zero vitamin C and E” [7]. In the Netherlands we were not even able to perform a small phase II trial with certain nutrients for the simple reason that most people already took them.

What can we learn from these negative trials (the SELECT trial and this PHS II-trial)?

  • Previous positive results were probably due to chance. In the future a better preselection of compounds and doses in Phase 2 trials should determine which few interventions make it through the pipeline (Gann, Schroder).
  • Many other trials disprove the health benefits of high dose vitamins and some single vitamins may even increase risks for specific cancers, heart disease or mortality [9]. In addition vitamin C has recently been shown to interfere with cancer treatment [10].
  • The trials make it highly unlikely that vitamins prevent the development of prostate cancer (or other cancers) when given as a single nutrient intervention. Instead, as Dr Sasso puts it “At the end of the day this serves as a reminder that we should get back to basics: keeping your body weight in check, being physically active, not smoking and following a good diet.”
  • Single vitamins or high dose vitamins/antioxidants should not be advised to prevent prostate cancer (or any other cancer). Still it is very difficult to convince people not taking supplements.
  • Another issue is that all kind of pharmaceutical companies keep on pushing the sales of these “natural products”, selectively referring to positive results only. It is about time to regulate this.

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Sources & other reading (click on grey)

  1. Huge disappointment: Selenium and Vitamin E fail to Prevent Prostate Cancer.(post on this blog about the SELECT trial)
  2. Podcasts: Cochrane Library and MedlinePlus: (post on this blog)
  3. Vitamins E and C in the Prevention of Prostate and Total Cancer in Men: The Physicians’ Health Study II Randomized Controlled Trial. J. Michael Gaziano et al JAMA. 2008;0(2008):2008862-11.[free full text]
  4. Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers: The Selenium and Vitamin E Cancer Prevention Trial. Scott M. Lippman, Eric A. Klein et al (SELECT)JAMA. 2008;0(2008):2008864-13 [free full text].
  5. Randomized Trials of Antioxidant Supplementation for Cancer Prevention: First Bias, Now Chance-Next, Cause. Peter H. Gann JAMA. 2008;0(2008):2008863-2 [free full text].
  6. Combined lycopene and vitamin E treatment suppresses the growth of PC-346C human prostate cancer cells in nude mice. Limpens J, Schröder FH, et al. J Nutr. 2006 May;136(5):1287-93 [free full text].

    News
  7. The New York Times (2008/11/19) Study: Vitamins E and C Fail to Prevent Cancer in Men.
  8. BBC news: (2008/12/10) Vitamins ‘do not cut cancer risk’.
  9. The New York Times (2008/11/20) News keeps getting worse for vitamins.
  10. The New York Times (2008/10/01) Vitamin C may interfere with cancer treatment.




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