Greater levels of selenium,
vitamin E and the tomato carotenoid
lycopene have been shown to reduce prostate cancer in one out of every
four Caucasian males, or those who inherit a specific genetic
variation that is particularly sensitive to oxidative stress, say US
researchers.
Conversely, if carriers of this genetic variant have low levels of
these vitamins and minerals, their risk of aggressive prostate
increases substantially, as great as 10-fold, over those who maintain
higher levels of these nutrients, they write in today's issue of
Cancer Research.
"This large prospective study provides further evidence that oxidative
stress may be one of the important mechanisms for prostate cancer
development and progression, and adequate intake of antioxidants, such
as selenium, lycopene and vitamin E, may help prevent prostate
cancer," said Dr Haojie Li, a researcher at the Brigham and Women's
Hospital and Harvard Medical School.
The new findings are based on an analysis of 567 men diagnosed with
prostate cancer between 1982 and 1995, and 764 cancer-free men from
the Physicians Health Study.
The initial goal of this study was to assess the effect of
aspirin and
beta-carotene on men's health. Li's team decided to check for variants
of the gene that codes for manganese superoxide dismutatase (MnSOD),
an important enzyme that works as an antioxidant in human cells to
defend against disease.
The MnSOD gene is passed from parents to offspring in one of three
forms: VV, VA or AA.
"Compared with men with the MnSOD VV or VA genotype, people with the
AA genotype seem to be more sensitive to the antioxidant status," said
Li. "Men with the AA genotype are more susceptible to prostate cancer
if their antioxidant levels are low."
The study's results found that a quarter of the men in the study
carried the MnSOD AA genotype, half carried the VA genotype, and the
remaining quarter carried the VV genotype.
The results indicated that the VA and VV men were at equivalent risk
for developing prostate cancer across all levels of antioxidants in
their blood.
But compared to MnSOD VV or VA carriers in the lowest quartile of
selenium levels, MnSOD AA males had an 89 per cent greater risk for
developing aggressive prostate cancer if they had low blood levels of
the mineral.
On the other hand, MnSOD AA carriers with high selenium - those men in
the highest quartile - had a 65 per cent lower risk than the MnSOD VV
or VA males who maintained low levels of selenium.
"The levels of selenium in the highest quartile of these men are not
abnormally high," Li said. "Our range is neither extremely high nor
extremely low."
While similar trends were observed for lycopene and vitamin E when
tested independently, the contrast in relative risk was most
pronounced for the men who had high blood levels for all three
antioxidants combined, said the researchers.
"Among men with the MnSOD AA genotype, we observed a 10-fold
difference in risk for aggressive prostate cancer, when comparing men
with high versus low levels of antioxidants combined,"said Li. "In
contrast, among men with the VV or VA genotype, the prostate cancer
risk was only weakly altered by these antioxidant levels."
"Our study, as well as many other epidemiological studies, encourages
dietary intake of nutrients such as lycopene from tomato products, or
supplements for vitamin E and selenium to reduce risk of prostate
cancer," said Li.
Prostate cancer is one of the biggest cancer killers in industrial
countries and affects more than 500,000 men worldwide every year. This
number is expected to increase with the ageing population.
Similar interactions between dietary antioxidants and the variations
in the MnSOD gene have previously been linked to risk for breast
cancer.
For more information visit:
http://www.prostacet.com/?aid=627156
Antioxidant levels key to prostate cancer risk in some men 
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