Evidence Mounts that Vitamin E Does Not Stop
Prostate Cancer, Nor Does Selenium, Vitamin C
JAMA publishes 2 studies released early in public
interest on supplements’ ineffectiveness in preventing cancer
Jan.
7, 2009 - 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. And, in a second study in today’s
Journal of the American Medical Association (JAMA), long-term
supplementation with vitamin E or C did not reduce the risk of prostate
or other cancers. Both reports were released early online in December due to public
health implications.
March 3, 2006 – Vitamin E – good or bad – has been
a hot topic in medicine for the last couple of years. New research at
Ohio State University, looking at how two forms of vitamin E act inside
animal cells, has concluded this powerful antioxidant, popular with
senior citizens, is "truly a
double-edged sword."
Read more...
An editorial in the same JAMA issue says,
“Physicians should not recommend selenium or vitamin E - or any other
antioxidant supplements - to their patients for preventing prostate
cancer."
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. men, with approximately 186,000 new
cases and 29,000 deaths (the second leading cause of cancer death)
estimated for 2008.
An effective prevention strategy for prostate
cancer would have substantial public health benefits, according to
background information. Previous studies have indicated the potential of
selenium and vitamin E for preventing prostate cancer.
The Selenium and Vitamin E Study
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 + 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 Says Don’t Recommend Antioxidants to
Prevent Prostate Cancer
In a JAMA editorial, Peter H. Gann, M.D., Sc.D., of
the University of Illinois at Chicago, comments on the "disappointing
news" that two major trials (SELECT and Physicians' Health Study II,
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 E—or any other antioxidant supplements—to
their patients for preventing prostate cancer."
Second Study – Vitamin C nor E reduce risk of
cancer
In the second report, a major cancer prevention
study, long-term supplementation with vitamin E or C did not reduce the
risk of prostate or other cancers for nearly 15,000 male physicians,
according to the other report published in JAMA today.
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.
Keep up with the latest news for senior citizens, baby
boomers
Jan.
7, 2009 - 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. And, in a second study in today’s
Journal of the American Medical Association (JAMA), long-term
supplementation with vitamin E or C did not reduce the risk of prostate
or other cancers. Both reports were released early online in December due to public
health implications.