Vitamins C, E and Selenium Fail to Prevent Prostate
Cancer in Massive Studies
Do not work against other cancers either say
studies released early by JAMA
Dec.
9, 2008 Two major cancer prevention studies have found that two of the
most popular vitamins E, and C - nor the supplement selenium do not
lower the risk for prostate cancer, or other cancers. Both studies will
be published January 7 in the Journal of the American Medical
Association (JAMA)
but are bring released early because of the important public health
implications.
The
number of prostate cancer deaths in the United States has declined in
recent years, but this cancer remains one of the most common
malignancies in U.S. senior men, with approximately 186,000 new cases
and 29,000 deaths (the second leading cause of cancer death) estimated
for 2008.
Vitamin E and C Study
The
research finding long-term supplementation with vitamin E or C did not
reduce the risk of prostate or other cancers for nearly 15,000 male
physicians is considered a major study..
In
some observational studies, intake or blood levels of vitamins E and C
have been associated with reduced risk of certain cancers.
"However, definitive proof that vitamins E and C can reduce the risk of
overall or site-specific cancers must rely on large-scale randomized
trials," the authors write.
"A
number of trials have addressed the potential role of vitamins in the
prevention of cancer; however, the results from these trials have not
been consistent."
Despite uncertainty about the long-term health effects or benefits, more
than half of U.S. adults take vitamin supplements, and vitamins E and C
are among the most popular individual supplements, according to
background information in the article.
J.
Michael Gaziano, M.D., M.P.H., of Brigham and Women's Hospital and VA
Boston Healthcare System, Boston, and colleagues conducted the
Physicians' Health Study II, a randomized, placebo-controlled trial to
examine the effects of vitamin E and vitamin C on prostate cancer and
total cancer.
The
study included 14,641 male physicians in the United States, age 50 years
or older at the time of entering the trial, of whom 1,307 had a prior
history of cancer. Participants were randomized to receive individual
supplements of 400 IU of vitamin E every other day and 500 mg. of
vitamin C daily.
During an average follow-up of 8.0 years, there were 1,943 confirmed
total cancer cases and 1,008 prostate cancer cases.
Compared with placebo, vitamin E had no effect on the incidence of
prostate cancer or total cancer. The researchers also found no
significant effect of vitamin C on total cancer or prostate cancer.
Neither vitamin E nor vitamin C had a significant effect on
site-specific cancers, including colorectal, lung, bladder and
pancreatic. Stratification by various cancer risk factors demonstrated
no significant modification of the effect of vitamin E on prostate
cancer risk or either agent on total cancer risk.
"These data provide no support for the use of these supplements in the
prevention of cancer in middle-aged and older men," the authors
conclude.
Vitamin E and Selenium Study
In
perhaps the largest cancer chemoprevention trial ever conducted,
researchers have found that supplementation with vitamin E or selenium,
alone or in combination, was not associated with a lower risk of
prostate cancer or other cancers.
Previous studies have indicated the potential of selenium and vitamin E
for preventing prostate cancer.
Scott M. Lippman, M.D., of the University of Texas M. D. Anderson Cancer
Center, Houston, and Eric A. Klein, M.D., of the Cleveland Clinic Lerner
College of Medicine, Cleveland, and colleagues conducted the Selenium
and Vitamin E Cancer Prevention Trial (SELECT) to examine the effects of
selenium and vitamin E, alone or in combination, on the risk of prostate
cancer and other health outcomes in relatively healthy men.
The
trial included 35,533 men, age 50 years or older for African-American
men and age 55 years or older for other men at the start of the study,
from the U.S., Canada, and Puerto Rico. The participants were randomly
assigned to receive one of four interventions between August 2001 and
June 2004 for a planned minimum follow-up of 7 years: selenium (200
μg/day); vitamin E (400 IU/day), selenium + vitamin E, or placebo.
On
September 15, 2008, the independent data and safety monitoring committee
recommended the discontinuation of study supplements because the
alternative hypothesis of no evidence of benefit from either study agent
was convincingly demonstrated and there was no possibility of a benefit
to the planned degree with additional follow-up.
The
notice to discontinue study supplements went out to all active study
sites on October 23, 2008, when median (midpoint) overall follow-up was
5.46 years.
The
researchers found that there were no statistically significant
differences in the absolute numbers (or ● 5-year incidence rates) of
prostate cancer diagnoses between the four groups:
● placebo, 416 cases (5-year rate of 4.43 percent);
● selenium, 432 cases (4.56 percent);
● vitamin E, 473 cases (4.93 percent);
● selenium + vitamin E, 437 cases (4.56 percent).
There were nonsignificant increased risks of prostate cancer in the
vitamin E group and type 2 diabetes mellitus in the selenium group, but
not in the selenium plus vitamin E group.
"In
conclusion, SELECT has definitively demonstrated that selenium, vitamin
E, or selenium + vitamin E (at the tested doses and formulations) did
not prevent prostate cancer in the generally healthy, heterogeneous
population of men in SELECT.
These data underscore the prudence that is needed in considering
recommendations to use agents for the prevention or control of disease
in the absence of convincing clinical trial results. These findings also
compel the medical research community to continue the search for new,
effective agents for prostate cancer prevention," the authors write.
Editorial: Randomized trials
of antioxidant supplementation for cancer prevention-first bias, now
chancenext, cause
In
an editorial, Peter H. Gann, M.D., Sc.D., of the University of Illinois
at Chicago, comments on the "disappointing news" that two major trials
(which were "conceived during the wave of hope" of earlier studies
suggesting that cancer might be prevented by selenium or vitamin E)
showed that neither selenium nor vitamin E produced any reduction in
prostate cancer or other cancers.
"...single-agent interventions, even in combinations, may be an
ineffective approach to primary prevention in average-risk populations.
It may be time to give up the idea that the protective influence of diet
on prostate cancer risk...can be emulated by isolated dietary molecules
given alone or in combination to middle-aged and older men.
...On the other hand, nonpharmacological dietary prevention of prostate
cancer is probably more complex and may involve certain inconvenient
truths. Fortunately, no dietary change this profound is likely to be
beneficial for prostate cancer alone. If it requires whole foods,
extracts, or dietary patterns, it may be necessary to give up the
reductionist need to know which molecule is most responsible and perhaps
give up the notion of placebo controls as well."
"Epidemiology teaches that every statistical association has only 3
possible explanations: bias, chance, and cause. Regarding nutritional
prevention of prostate cancer, first-generation phase 3 trials were too
reliant on biased interpretation of prior research, second-generation
trials may have been too reliant on chance, yet there is every reason to
believe that the next generation will have a firmer basis for causal
hypotheses.
Until then, physicians should not recommend selenium or vitamin Eor
any other antioxidant supplementsto their patients for preventing
prostate cancer."
Keep up with the latest news for senior citizens, baby
boomers
