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Selenium
(March 2006)
It’s going to be long wait until 2012 when the results
become available from the large SELECT trial evaluating possible benefit
for selenium (Se) and Vitamin E in prostate cancer prevention. However for
impatient persons, currently it could be considered a “good bet” that the
intake of 200 mcg. of selenium confers benefit in lowering the risk and
aggressiveness of prostate cancer. In vitro evidence suggests that
selenium is anticarcinogenic by promoting apoptosis, inhibiting
angiogenesis and cellular proliferation, and serving as an antioxidant.
However, the strength of evidence is diminished by some
important qualifications. The Nutritional Prevention of Cancer Trial (NPCT)
compared supplemental 200 mcg Se to placebo, and at 7.4 years of follow-up
prostate cancer incidence was reduced by 64%, but only
in those men with low baseline Se levels, i.e. <125 ng/mL.
Similar findings were reported from the analysis of the
Physicians’ Health Study (PHS), best summarized in the Am. J. of Urol.
Rev., Jan 2005. This study was based on 13 year follow-up data of 22,071
healthy male physicians and it evaluated the incidence of prostate cancer
in relation to dietary history. A 48% reduction of the risk of
advanced, i.e., Stage C and D, cancer was seen, but
only was seen in the men in the lowest quintile of baseline
Se levels who also had baseline PSA values of > 4 ng/mL. A comparatively
high level of selenium was associated with a statistically non-significant
22% reduction in the overall incidence of prostate cancer.
The superior risk reduction seen in the NPCT trial could
have resulted from the higher (190 ng/mL) mean level of Se in the NPCT
patients achieved by the 200 mcg supplements compared to the mean level of
104 ng/ml seen in the PHS wherein physicians freely chose their diets.
A literature meta-analysis by Canadian researchers (Cancer Causes Control,
2005 Nov) was more generally supportive of benefit for lycopene and found
a 26% risk reduction from moderate dietary Se intake (no Se
supplementation). They reported that “A dose-response trend was observed
when we stratified the studies by disease severity”.
Short of actually measuring the serum or
toenail level of Se, an individual would be betting on the side of
strongest evidence by taking 200 mcg. Of supplemental Se.
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