All:
It's supplement company dogma that selenium supplements higher than the 55 mcg RDA prevent cancer and reduce mortality; this is based on (to quote myself):
the Nutritional Prevention of Cancer Study, the big RCT of selenium vs skin cancer whose initial results were very promising for Se: there was no reduction in skin cancer risk (the primary endpoint), but "Analysis of secondary end points revealed that, compared with controls, patients treated with selenium had a nonsignificant reduction in all-cause mortality (108 deaths in the selenium group and 129 deaths in the control group [RR; 0.83; 95% CI, 0.63-1.08]) and significant reductions in total cancer mortality ..., total cancer incidence ..., and incidences of lung, colorectal, and prostate cancers." (1) Subsequent reports detailed those results, parsing them out for individual cancer sites.
This result led to every damned Se supplement out there containing the 200 mcg dose used in the trial, and is cited everywhere as definitive proof of Se supplementation's ability to reduce cancer incidence & mortality. This was initially a reasonable enough conclusion (tho' it was not properly emphasized that the population was intentionally chosen from an area with unusually low-selenium soils (the Eastern USA), thus making the cohort result dubiously-extrapolable to the population at large (there would be many more frankly deficient people in this group than most places in the industrialized world) -- and even here, according to this new report on diabetes risk (7), "the average dietary selenium intake is 90 mcg/d; this value is low for the United States but is much greater than that required to optimize selenoenzyme activities" -- which is the cutoff on whose basis they set the RDA (of "only" 55 mcg). ...
Since then, however, additional analysis has shown this to be a dangerous oversimplification. Subsequent reports from the NPC (1-5) as well as animal studies (eg, (6)) have shown that this dose of Se gives no add'l benefit to some cancers, and may INCREASE the risk of others. These studies find that basically all of the benefits come from correcting frank (sub-RDA) selenium deficiency, with people who already have normal Se intake in their diet getting no benefit for some cancers, and increases in risk for others. The ongoing, unqualified, dogmatic repetition of the cancer claim now constitutes borderline-criminally-negligent oversimplification -- especially when, as when a Certain Supplement Company with which I used to be in a competitive relationship was wont to do, companies cite multiple reports from this SAME STUDY as if they were SEPARATE trials, each independently confirming Se's ability to protect from cancer...
... and, as detailed in that post (which I encourage you to read either before or after this one, for much more detail & proper citations), they then went on to find an increase in diabetes in the supplemented group.
With that as background: it was on the basis of the original result of the Nutritional Prevention of Cancer Study that the National Cancer Institute launched SELECT:
the Selenium and Vitamin E Cancer Prevention Trial, a clinical trial to see if one or both of these substances can help prevent prostate cancer when taken as dietary supplements. ... Enrollment for the trial began in 2001 and ended in 2004. More than 400 sites in the United States, Puerto Rico, and Canada are taking part in the study. Over 35,000 men are participating in SELECT ... The amount of selenium (provided as l-selenomethionine) was 200 micrograms (µg) daily. ... The amount of vitamin E (provided as dl-alpha-tocopherol acetate) was 400 milligrams (mg), which is equivalent to 400 International Units (IU) per day.
Well, now they've pulled the plug on it early, because the results are coming in similarly to the ultimate conclusions of the smaller NPCS:
Now, people (especially, but not only, supplement companies) are going to say that the results were not statistically significant -- which is true, but again, they are consistent with previous such reports, which makes me suspect a small, but real, effect; certainly, having one trial after another come in with no benefit or a small risk makes it pretty darned clear that they aren't doing anything good.Prostate Cancer Prevention Study Halted - Vitamin E, Selenium No Help in Preventing Prostate Cancer
By Daniel J. DeNoon
WebMD Health News
Reviewed by Louise Chang, MD
Oct. 28, 2008 -- The National Cancer Institute has halted its $114 million study of whether vitamin E and selenium can prevent prostate cancer.
They can't [prevent prostate cancer] -- at least not in the formulations and dosages used in the study, called SELECT (SELenium and vitamin ECancer prevention Trial). The safety panel for the 35,000-man study called for a halt when an early look at the data showed no benefit for the treatment.
There were slightly more prostate cancers in men taking vitamin E alone, and slightly more diabetes in men taking only selenium. But neither finding was statistically significant, meaning they were likely due to chance. [Actually, since these same results were also found in the NPCS (for diabetes) and in other RCTs using alpha-tocopherol (for prostate cancer), I'm inclined to suspect a real, but small, effect -MR].
"The data to date suggest, but do not prove, that vitamin E may slightly increase the chance of getting prostate cancer, and that selenium may increase the chance of getting diabetes mellitus," warns a letter sent to study participants by the Southwest Oncology Group, which ran the NCI-funded study. [That's a better summary IMO - MR].
Study participants were told to stop taking the two pills they'd been taking every day since the trial opened in 2001. The men received either vitamin E (400 milligrams) and selenium (200 micrograms), vitamin E and placebo, selenium and placebo, or placebos alone.
People will also say that they used the wrong forms. I'm inclined to suspect this may very well be true. It's pretty darned clear that people need to stop taking straight alpha-tocopherol; I suspect that the 'right' supplement, if such exists, is high-gamma mixed tocopherols and tocotrienols with <30% total alpha-tocopherol (and, I'm inclined to say, <30 IU of total alpha-tocopherol IAC), and for Se, Se-methylselenocysteine -- please see my discl0sure, which is extremely relevant to both of these recommendations. But take a step back. There is not anywhere near the level of evidence in support of a benefit of these supplements (largely very artificial animal studies; far fewer total scientific reports vs the standard forms; and no human clinical trials with clinical outcomes).
And, of course, supplement companies and others will pretend that a zillion other studies contradict these. But they'll use much weaker kinds of evidence -- epidemiology instead of clinical trials, or clinical trials with surrogate outcomes, or they'll play 'echo chamber' by citing multiple reports of the same benefit from the same study as if they were separate clinical trials, as was routinely done with the NPCS.
I put it to you all that this engine of marketing and speculation is not a good basis on which to gamble your long-term health.
I strongly urge everyone to go over your collection of pill bottles, and ask yourself, seriously, why you're taking it. What is the evidence, in normal, healthy humans, of a benefit? Is this a supplement proven beneficial for a specific disease that you already have by large, long-term, randomized clinical trials? Have you carefully analyzed your quotidian diet using excellent nutritional software like CRON-O-Meter, and decided to take a specific supplement to correct your own diet's specific nutritional shortcomings, using doses similar to what is available from a healthy diet and/or the RDA?
If not, what are you putting into your body, and why?
The day of megadosing as a reasonable gamble for life-extensionists -- of 'it can't hurt, and it might help', of a speculative 'bridge to a bridge' -- is over. The evidence actually available is that high-dose vitamins and minerals don't help, and may harm; the "evidence" to the contrary is speculation and bluster.
You can't reach 'escape velocity' if you kill yourself first.
-Michael
Edited by Michael, 30 October 2008 - 10:20 PM.
