Vitamin E increases prostate cancer risk?

Will a new study end vitamin E as a dietary supplement for men?

The study in the Journal of the American Medical Association reports that “dietary supplementation with vitamin E significantly increased the risk of prostate cancer among healthy men.”

The study would seem to have some merit as it is clinical trial-ish, involved 35,533 men who were followed for 7-12 years and produced statistically significant results. The researchers estimate that vitamin E supplementation increases prostate cancer risk by 1.6 extra cancers per 1000 person-years.

So what’s the problem?

Though statistically significant, the results were weak (i.e., a relative risk of 1.17) and only marginally (if not suspiciously) statistically significant (i.e., the lower bound of the 95% confidence interval was 1.004).

While clinical trials can conceivably get away with weaker statistics — i.e., they tend to be more highly-controlled than, say, case-control epidemiology — this one fails the mark for two reasons.

Although the study subjects were provided with vitamin supplements, no one knows how well study subjects adhered to the vitamin regiment. So intake of vitamin E is somewhat uncertain, a problem for weak statistical results.

Next and perhaps more importantly, it’s not at all clear that data were collected on potential confounding risk factors for prostate cancer. The study, if its omission of potential confounders from mention is any indication, dubiously pretends that vitamin E supplementation is the only risk factor for prostate cancer. [Note: The lead study author assures me that family history and other confounders were considered but we await confirmation of this.]

Finally, the researchers acknowledge that they have no idea how vitamin E supplementation could possibly alter prostate cancer risk:

A biological explanation for the observed increased risk of prostate cancer in the vitamin E arm [of the trial] is not apparent from these data.

So while it’s not clear that vitamin E supplementation does any good, this study does not constitute evidence that it causes any harm.

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8 responses to “Vitamin E increases prostate cancer risk?

  1. The FDA is trying to regulate vitamins.

  2. Pingback: Vitamin E increases prostate cancer risk? | JunkScience.com | The Cancer Site

  3. The AMA has been trying to get vitamins under prescription control for decades. We can’t have people taking their health into their own hands.

  4. Glad for your criticism – had read the same WSJ article, and wondered just how significant the result was.

    Minor typo: “vitamin regiment” should read “vitamin regimen”.

    – Jerry

  5. Michelle Summers

    So, tens of thousands of men in the study and the Vitamin E group had 575 occurences of prostate cancer vs. the placebo group’s 529 occurences.. Pretty close numbers…. Good science asks: What sort of Vitamin E was used? Was it a cheap synthetic product? Was the e oil contaminated with even small amounts of mercury or pesticides? This is not an unheard of ingredient in cheap vitamins. If so, any of these could cause a small increase in cancer.. I would not let these results deter me from taking Vitamin E and my husband feels the same way. -Michelle Summers

  6. This reminds me of the classic and vintage Lucille Ball skit with “Vita-Meata-Vegimin” and all it did was to make her falling down drunk!

    Another “research project” independently replicating the null set.

  7. If the subjects were supplied with the Vitamin E, I am sure that it was synthetic. I always laugh when I hear allopathic physicians declare that there is no difference between natural and synthetic E. I guess the difference in opinion is that I did not sleep during my biochemistry classes and I had 123 hours of nutrition classes compared to their 0 to 7 hours. This report and the older women taking vitamins and minerals report were a typical quarterly scare tactic by pharma. Please discuss this with friends and relatives.

  8. Pingback: Secret science: Researchers refuse to provide data in vitamin E-prostate cancer study | JunkScience.com

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