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Antioxidant levels key to prostate
cancer risk in some men
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.
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